Contribution of primary motor cortex to compensatory balance reactions

David A E Bolton
Laura Williams
W Richard Staines
William E Mcilroy
Contribution of primary motor cortex to compensatory balance reactions
R E S E A R C H A R T I C L E Open Access
Background: Rapid compensatory arm reactions represent important response strategies following an unexpected loss of balance. While it has been assumed that early corrective actions arise largely from sub-cortical networks, recent findings have prompted speculation about the potential role of cortical involvement. To test the idea that cortical motor regions are involved in early compensatory arm reactions, we used continuous theta burst stimulation (cTBS) to temporarily suppress the hand area of primary motor cortex (M1) in participants prior to evoking upper limb balance reactions in response to whole body perturbation. We hypothesized that following cTBS to the M1 hand area evoked EMG responses in the stimulated hand would be diminished. To isolate balance reactions to the upper limb participants were seated in an elevated tilt-chair while holding a stable handle with both hands. The chair was held vertical by a magnet and was triggered to fall backward unpredictably. To regain balance, participants used the handle to restore upright stability as quickly as possible with both hands. Muscle activity was recorded from proximal and distal muscles of both upper limbs.Results:Our results revealed an impact of cTBS on the amplitude of the EMG responses in the stimulated hand muscles often manifest as inhibition in the stimulated hand. The change in EMG amplitude was specific to the target hand muscles and occasionally their homologous pairs on the non-stimulated hand with no consistent effects on the remaining more proximal arm muscles. Conclusions: Present findings offer support for cortical contributions to the control of early compensatory arm reactions following whole-body perturbation.

Background

Compensatory reactions to sudden loss of balance involve the coordination of multiple body segments acting rapidly to restore stability. The mechanisms underlying these reactions likely reflect distributed neural networks ranging across spinal and brain stem regions up to higher cortical centres [1][2][3]. While postural regulation was historically regarded as sub-cortical in nature, more recent accounts include speculation about cortical contributions to the control of reactive balance [4][5][6][7][8][9][10]. In fact, even elements of neural function largely considered separate from posture, such as attention and working memory, reveal an interaction of postural control with higher executive networks [11][12][13][14]. Although a cortical role in reactive balance is now more widely accepted, there remains a perspective that the very early corrective reactions are driven primarily via sub-cortical mechanisms, and only the later phases of these reactions are significantly influenced by cortical drive [15].

Recent work in our lab revealed that temporary suppression of the hand region of primary motor cortex (M1) using a continuous theta burst stimulation (cTBS) pattern of transcranial magnetic stimulation attenuated hand muscle responses during a compensatory reach to grasp [16]. Focal suppression of rapid compensatory hand muscle activity indicated that M1 contributed to producing or at least scaling of the initial response. Importantly, this same pattern of suppression was noted when reaching in response to an auditory cue suggesting that both perturbation-evoked and auditory-cued arm actions were mediated through a similar cortical network. These results extend upon previous work by Gage and colleagues which revealed a preservation of spatialtemporal reach patterns during volitional and compensatory reaching [17]. Remarkably, these authors noted that despite similar muscle activity and arm kinematics, perturbation-evoked reaches were approximately twice as fast. One proposed explanation for this phenomenon is that heightened arousal drives the same cortical networks involved in producing a cortically mediated reach at a much faster rate [18,19].

In general, the recovery of balance can be achieved either by engaging muscles to re-establish a stable position over a fixed support base or to establish a new support base to catch a falling centre of mass (e.g. taking a step or grabbing a handrail). These strategies have been referred to as fixed support reactions or change of support reactions respectively [20]. In the two studies described above by Gage et al. (2007) and Bolton et al. (2011), subjects were perturbed while seated in a chair and prompted to grasp a secure handhold, therefore this represents a change of support reaction. Although the previous results offered support for the role of M1 in this corrective action it is notable that hand muscles were activated at a later stage in the reaching response. This is consistent with change of support actions which tend to recruit muscles in a proximal to distal arrangement during the reach to grasp [17,20]. While these previous studies have revealed cortical contributions to compensatory reach to grasp, it remains unclear whether the earliest compensatory responses are similarly mediated by cortical pathways. In order to explore the earliest compensatory reactions one must focus on the earliest muscle responses during execution of fixed support reactions.

The present study explored the role of M1 in the earliest postural reactions during a fixed arm support paradigm. Our specific goal was to investigate the contribution of M1 to the early compensatory arm response to rapid chair tilts while holding a fixed handle with both hands. By temporarily suppressing cortical excitability of the hand area of M1 (left hemisphere) we hypothesized that the very early hand response would be diminished in the right hand during a fixed support reaction. Moreover, given the established interaction between right and left M1 [21] we investigated the potential impact on the contralateral (left) hand. There is evidence to suggest that the predominant influence of M1 onto the contralateral M1 is inhibitory, thus inhibition of M1 on one hemisphere may result in a facilitation of homologous muscles in the contralateral M1 [21]. Some support for this idea comes from a recent study when faster reaction times for hand muscles were recorded when the contralateral M1 was temporarily suppressed [22]. Although present results revealed some variety in the precise way cTBS influenced muscle activity across subjects, there was consistently a focal impact of cTBS on the stimulated hand muscles (and occasionally homologous muscle pairs) while more proximal muscles were unaffected. Overall, these results suggest that cortical networks contribute to early compensatory arm reactions following whole-body perturbation.

Results

The sequence of muscle activity following perturbation revealed that wrist flexor (WF) was the fastest responder for both the right (150.3 ± 5.8 ms) and left (149.6 ± 4.2 ms) limbs with the remaining muscles (first dorsal interosseous (FDI), abductor pollicis brevis (APB), and biceps brachii (BIC)) engaged approximately 20 ms later (FDI R : 169.4 ± 4.4 ms; APB R : 173.4 ± 5.2 ms; BIC R : 168.1 ± 5.1 ms; FDI L : 164.2 ± 5. ms; APB L : 166.8 ± 3.3 ms; BIC L : 170.6 ± 5.5 ms). This sequence of muscle onsets (i.e. WF engaged prior to BIC) is consistent with previously mentioned fixed-support reactions where there is a distal to proximal order of muscle activation. Moreover, the onset latency of about 150 ms for the fastest response muscle (WF) is much faster than the earliest muscle onsets involved with rapid voluntary movements using similar speeded-limb response paradigms [16,17]. This provides support for the notion that the presently observed data represent reactive balance responses.

In order to probe our specific research question it was important to establish the efficacy of cTBS in suppressing cortical excitability over the stimulated hand region. To this end, our results showed a significant drop of 23% (SE ± 9%) in MEP amplitude in FDI following cTBS in the 9 subjects where MEPs were collected (t 8 = 2.56, p = 0.035).

The influence of cTBS on the fixed support balance reactions was determined by comparing difference scores (post-cTBS vs pre-cTBS) which revealed a statistically significant difference in the amplitude of perturbationevoked responses comparing between hand and arm muscles (F 1,13 = 7.52, p = 0.018; Figure 1). Follow-up comparison revealed that Hand R response amplitudes were significantly different following cTBS compared to Arm R , (t 13 = 2.92, p = 0.013), but there were no significant differences when comparing left side Hand L and Arm L (t 13 = 0.996, p = 0.162).

While a clear group difference was observed, there was inter-subject variability in the specific impact of cTBS on hand muscles which we believe may reflect, in part, the specificity of the applied cTBS. Figure 2 demonstrates an example where FDI and APB are both inhibited on the right hand, but no change in proximal muscle activation. The impact of cTBS on the stimulated hand muscles is depicted for each of the 14 subjects in Figure 3. Overall, 9 of 14 (s1-s9) subjects revealed significant suppression of the fixed support reaction in one or both of the right hand muscles (see Figure 3). In the remaining subjects there was no significant inhibition of the response amplitude in either of the muscles of the right hand.

Comparison of EMG latencies revealed a trend for an interaction on the stimulated right arm (F 3,33 = 2.55, p = 0.07). Follow-up comparison indicated that APB responses became marginally slower (by 8.4 ± 4.6 ms) post-cTBS in the stimulated right hand (t 11 = 1.82, p = 0.048). There was a main effect of muscle (Right hand: F 3,33 = 11.82, p < 0.001; Left hand: F 3,33 =26.003, p < 0.001) with WF having the earliest response in both arms, followed by FDI and BIC at approximately the same latency, and finally APB. The onset time for each muscle is shown in Figure 4 (a). Theta burst stimulation demonstrated no significant impact on EMG onset in most of the muscles tested (the exception with a trend in APB noted above). The general preservation of response onset following stimulation for all muscles is demonstrated in Figure 4 (b) expressing post versus pre-cTBS onsets as a percentage.

Discussion

The present study investigated the role of M1 in compensatory upper limb responses to whole body perturbation when holding a fixed support handle. To address this question cTBS was used to target cortical suppression over the hand area of the left M1 prior to the testing of perturbation-evoked compensatory fixed support reactions of the upper limb. Our results indicated that early responses of distal muscles targeted by the cTBS were indeed altered following stimulation, in the form of suppressed FDI and/or APB activity of the right hand. It is noteworthy that the influence of cTBS on these early balance reactions was often complex and evident as an interaction between FDI and APB of the same hand (e.g. a decrease in one muscle was often associated with an increase in the other). Although cross-hand interactions were not as consistently observed, there were some subjects revealing an inverse relationship between distal muscle activity in the two hands even though muscles of

Right Left

Hand Arm Hand Arm Figure 1 The average change and standard error in EMG response amplitude following cTBS (i.e. difference score) is presented in bar graphs and expressed as a percentage of pre-cTBS values. The dark bars represent hand muscles (FDI and APB combined) and the grey bars represent arm muscles (WF and BIC combined) for the right and left sides separately. * denotes significant difference at p < 0.05. the left hand were not the direct target of the applied cTBS. In contrast, the proximal muscles involved in the balance reaction were not similarly influenced by the applied cTBS suggesting that the impact of cTBS was limited to the stimulated hand muscles and in some instances to their homologous muscle pairs on the nonstimulated M1. Overall, our results provide evidence for M1 in contributing to the initial fixed-support arm response following whole-body perturbation. More generally, these results provide further support for a cortical role in the control of early compensatory arm reactions.

Cortical role in early compensatory arm reactions

Although cortical contributions to reactive balance are now more widely accepted, the stage at which cortical regions influence corrective postural activity is unclear. Findings from reduced animal preparations demonstrate the presence of direction-appropriate righting mechanisms at sub-cortical levels [23], and human studies have indicated that at least some very early postural responses are triggered prior to direct cortical involvement [24]. Therefore the fact that sub-cortical networks are capable of producing highly coordinated corrective actions, along with transit times involved in traversing cortical sites has understandably shaped thinking that early compensatory actions are not significantly determined by cortical mechanisms. Indirect evidence suggests cortical contributions to reactive balance are not simply relegated to late-stage modifications of sub-cortically-initiated responses. As previously mentioned, Gage and colleagues (2007) observed identical motor patterns in the arm when reaching for a target handle during both compensatory and volitional reaching even though perturbation-evoked reaches were twice as fast. Remarkably, this was true despite subjects receiving the same instructions to reach as quickly as possible in both conditions. While subcortical mechanisms can certainly trigger rapid arm actions following a loss of balance, grasping a small target handle at a defined spatial location obviates some degree of visual guidance over the reach. Even with the prospect of descending priming over sub-cortical structures to selectively boost responsiveness [25] cortical guidance over the reach trajectory is likely needed to secure the hand onto the target handle. To explain how similar neural pathways could be engaged to produce the same reach at such an accelerated pace it has been proposed that the threat associated with whole-body perturbation heightens arousal which allows the central nervous system to overcome limits normally imposed on voluntary reaction times [18,19]. Thus the processing speed via cortical networks may be more rapid than would be normally determined from voluntary reactions. Recently, a clear role for M1 in producing or at least scaling early compensatory arm responses was confirmed more directly by Bolton et al. (2011) where cTBS was used to suppress the hand area of M1 [16].

The results of that study demonstrated suppression of the EMG responses in cTBS-targeted hand muscles of the reaching arm for both volitional and compensatory reaches offering further evidence for M1 as part of a common reaching network. Present findings extend upon the past study by revealing a similar suppression in response muscles when these muscles are engaged earlier in the response pattern (i.e. distal to proximal order with a fixedsupport balance reaction).

Notably, our present paradigm focuses on the most rapid fixed support reactions that are evoked in response to postural perturbation from muscles of a limb that is already in contact with a support surface [20]. With the arms fixed onto the support handle the current paradigm is distinct from the previous compensatory reach-to-grasp, or change-in-support reactions. Fixed support reactions do not require reach to target movements that are critical to change-in-support balance reactions, such as a reach-to-grasp. With the hands already in contact with a support surface the arms not only represent a means for righting the body but also provide sensory cues for the perturbation itself. This is an important distinction from our past work given that somatosensory cues offer critical signals to trigger the initial postural reactions [26]. Studies involving rapid stretch of the thumb [27] or of ankle extensors via rapid platform translation in standing subjects [24] have demonstrated both sub-cortically and cortically mediated reflexive actions countering the imposed postural disturbance. In fact in a standing balance context Taube et al. (2006) noted cortical involvement in the leg muscle response at latencies <100 ms [24]. Although such findings relate to cortical influences over postural responses it is important to recall that in these studies there is a direct stretch of the responding muscles, thus this cortical influence could potentially reflect a trans-cortical reflex loop acting through M1. Conversely, the muscle activity measured in the present study does not specifically arise from muscles undergoing direct stretch (e.g. not simply autogenic stretch responses). Therefore sensory cues originating from a variety of body regions, including cutaneous mechanoreceptors of the hands, may provide the trigger for the multi-joint upper limb balance reactions.

The specific role of M1 in the early compensatory arm reaction

Although our aim was to probe the role of M1 in early compensatory arm responses generally, the manner in which these responses were influenced by the applied cTBS was complex. Specifically, the interaction between FDI and APB within the same hand was unexpected. From our previous study using the change-in-support model, both hand muscles demonstrated a suppression of activity leading us to speculate that this would again be observed [16]. Presently, although some degree of suppression was common in at least one of the muscles of the stimulated hand, there were a number of subjects revealing a different relationship between FDI and APB activity. One plausible explanation for these results is the phenomenon of surround inhibition where intracortical inhibitory connections influence neighbouring cortical territory [28]. Surround inhibition has been demonstrated in a number of areas including M1 and has been suggested to account for discrete muscle activation thus allowing for fractionated movements of the hands [28,29]. Surround inhibition has been shown to be modulated based upon movement context and this has been specifically demonstrated between FDI and APB within the same hand [30] and has been shown to be quite variable between subjects [31]. Therefore it is possible that our results may reflect an interaction between hand muscle representations within M1, and the altered context for how the hands were used with a fixedsupport versus a reach-to-grasp response may account for the variability in the present study. An interesting finding was the relative preservation of response timing. This distinct impact of cTBS on response amplitude while leaving response onsets unaffected is consistent with our past results which focused on the change-in-support balance reactions [16]. Previously, we had noted suppressed response amplitudes in FDI and APB of the stimulated hand muscles while the remaining arm muscles were unaffected. Although the impact of cTBS on hand muscle activity is less consistent between subjects in the present study, a similar outcome was noted in that hand muscles were influenced in amplitude scaling but not onset. This may reinforce the idea that response scaling but not timing, is importantly influenced by activity within M1. Evarts noted that discharge from M1 neurons corresponded with the direction and amplitude of muscle forces required to produce movement [32]. Conversely, the selection of a motor synergy has been suggested to arise from more intermediate cortical stages of movement production such as the parietal and premotor regions [33,34]. Thus segregating the control of motor parameters in this way could result in preserving the onset of the compensatory arm pattern as a whole, while muscle amplitude is selectively diminished. Of course it was interesting to note there was a trend towards slowing of APB in the stimulated hand post-cTBS which may indicate that our present lack of influence over response timing may be a consequence of a failure to suppress M1 activity adequately below a given threshold to impact timing.

Conclusions

Present results provide support for a role of M1 in early compensatory arm reactions to whole-body perturbation. The application of cTBS over the motor region of the distal hand muscles led to a focal attenuation on the targeted hand responses with negligible impact on the proximal arm muscles. Further, these results add to our recent data using a reach-to-grasp model and indicate that this role is apparent in both change-of-support, as well as fixed-support corrective reactions involving the upper limbs. The present fixed-support model extends previous work by revealing cortical interactions both within and between motor cortices and suggests that M1 is involved in shaping and scaling the early compensatory arm behaviour to whole-body disturbance. Future studies will address how transferable these results are to standing balance paradigms and also compensatory responses involving the lower limbs.

Methods

Fourteen healthy adults (9 male, 5 female; 21-38 years old) participated in this study. All participant recruitment and data collection procedures were performed in accordance with and approved by the University of Waterloo's Office of Research Ethics. Informed written consent was obtained from all participants prior to testing (Note: consent was obtained from the subject photographed in Figure 5 to publish their picture). Participants were screened to verify that they were free of any neurological disorders prior to testing.

Participants sat in a custom-built chair that had the capability of tilting backwards in the sagittal plane to a maximum angle of 20 o causing a whole-body perturbation (shown in Figure 5a). The chair tilted backwards upon the release of an electromagnet (connected to a load cell), which held the chair upright. While sitting in the chair, participants were randomly exposed to temporally unpredictable perturbations. Upon receiving the perturbation participants were required to use the handle to pull themselves with both arms as quickly as possible to reposition the chair to an upright position. In between perturbations subjects were instructed to gently rest their hands on the support handle throughout testing while keeping their upper limbs as relaxed as possible. Testing order consisted of: (1) 20 pre-stimulation perturbation trials (pre cTBS), (2) cTBS applied when subjects were sitting quietly (no balance or perturbations required) followed by (3) 20 post-stimulation perturbation trials (post cTBS), for a total of 40 perturbations throughout the entire study (see Figure 5b). Electromyography was monitored from 8 muscles of the right and left upper limbs including: first dorsal interosseous (FDI), abductor pollicis brevis (APB), common wrist flexor (WF), and biceps brachii (BIC). Before any application of Ag-AgCl electrode pairs, the skin was prepared to reduce impedance using an exfoliate (NuPrep) and then cleansing agent (50/50 H 2 0 and ethanol solution). All analog data were converted with a 16-bit, 16 channel analog to digital (A/D) converter (National Instruments, Austin, TX, USA) sampled at 1000 Hz. The chair load (i.e. tensile load via the load cell) was dual-passed filtered with a 4 th -order Butterworth filter. The onset of the chair release was defined as the point when the chair load dropped 3 standard deviations below a resting baseline (note: this offers a conservative estimate of the perturbation onset). The EMG analyses were focused after the onset of the stimuli. EMG signals were conditioned with a bandpass (20-250 Hz) 2 nd -order Butterworth filter, and then corrected for bias and full-wave rectified. EMG onsets were defined as the moment that signals exceeded 3 standard deviations above resting baseline for 25 ms. Average amplitude of the EMG response was calculated for 100 ms following EMG onset.

Single pulse TMS and cTBS were both targeted over the FDI representation in left M1 using a 90 mm outer diameter figure eight coil with a MagPro stimulator (MCF-B65; Medtronic, Minneapolis, MN, USA). To determine the motor hotspot for FDI in M1 of each hemisphere, the stimulator coil was positioned over left M1 and oriented 45 degrees to the mid-sagittal line to induce a current. The motor hotspot was defined as the M1 location optimal for eliciting a motor evoked potential (MEP) in the contralateral relaxed FDI muscle, Resting motor threshold (RMT) was determined as the minimum single pulse intensity required to elicit MEPs of > 50 μV (peak to peak) in 5 out of 10 consecutive trials in subjects at rest. A percentage of this value (120% RMT) was then used for collecting thirty motorevoked potentials (MEPs) pre and 5 minutes post cTBS (in 9 of the subjects). The cTBS protocol consisted of 600 TMS pulses applied in the theta burst pattern (3 stimuli at 50 Hz repeated at 5 Hz) for 40 seconds at an intensity of 80% active motor threshold. The active motor threshold (AMT) was determined for each participant as the minimum single pulse intensity required to elicit MEPs of > 200 μV (peak to peak) in 5 out of 10 consecutive trials while subjects held approximately 10% of the maximum voluntary contraction of the FDI muscle. Next, using 80% of this value (80% AMT) we applied cTBS over the FDI target location on the left hemisphere. The procedures for cTBS are similar to those previously detailed by Huang and colleagues, [35].

Individual subject data was averaged separately pre or post-cTBS for each muscle within each arm. Response latencies were compared using two-way repeated measures ANOVA with 2 levels of testing time (pre and post) and 4 muscles (FDI, APB, WF, and BIC) for each arm separately. Significant interactions and main effects were followed-up using Tukey's post hoc analysis. For EMG average amplitude, preliminary analysis using repeated measures ANOVA failed to reveal significant differences related to cTBS. Upon further inspection of the data it was apparent that inter-subject heterogeneity was possibly preventing stimulation effects from being detected. To contend with the variable impact of stimulation on muscle responses, initial analysis was focused on comparing the absolute difference between pre and post-cTBS values. For this comparison, all response amplitudes for each muscle were first normalized by converting them into an absolute difference score (absolute difference score = |post cTBS valuepre cTBS value|/pre cTBS value). Moreover, to account for the possibility of stimulation effects on either the targeted FDI muscle and/or the adjacent APB representation, these muscles were grouped into a common 'Hand' representation for the right and left hands separately. Similarly, the WF and BIC were combined into an ' Arm' representation for each arm separately since we hypothesized proximal muscles would remain unaffected by cTBS. These groupings allowed us to compare the impact of stimulation on the target hand area versus the non-targeted proximal arm muscles. For analysis, two-way repeated measures ANOVA was used to compare the difference scores with two levels of muscle group (Hand versus Arm) and two levels of side of body (Right versus Left side). Significant effects were followed-up using paired t-test comparisons. Pre and post-cTBS MEP values were compared with a paired t-test. Data were transformed prior to analysis if they violated assumptions of normality. Significance was set at p < 0.05 for all comparisons.

Figure 2
2Single subject data showing both APB and FDI suppressed following cTBS.

Figure 3
3Average and standard error EMG amplitude responses for FDI and APB in the right hand following cTBS. Subject data grouped to demonstrate: both hand muscles suppressed (s1-5), one hand muscle suppressed while the other was facilitated (s6-10), or no significant change (s11-14). Note that all values are expressed as a percentage of pre-cTBS values and presented for each subject individually. * denotes significant difference at p < 0.05.

Figure 4
4EMG response latencies based on group average data (n = 14 subjects). Absolute values are depicted in the top graph (a). The graph below expresses the response onset latencies as a percentage of pre-cTBS values to demonstrate the overall lack of stimulation effect on EMG response timing (b).

Figure 5
5Chair-tilt apparatus depicted in (a) (maximum chair excursion for backward tilt = 20˚). Order of testing is presented in (b).
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AcknowledgementsThis work was supported by research grants to WEM and WRS from the Natural Sciences and Engineering Research Council of Canada and by funds from the Canada Research Chairs program to WRS. DAEB was supported by postdoctoral fellowships from the Ontario Ministry of Research and Innovation and the Heart and Stroke Foundation Centre for Stroke Recovery. The authors thank Jeff Rice for technical assistance.Competing interestsThe authors declare that they have no competing interests.Authors' contribution DAEB, WRS, and WEM provided concept/idea/research design. DAEB, LW, WRS, and WEM contributed to writing. DAEB and LW provided data collection. DAEB and LW provided data analysis. DAEB, WRS, and WEM provided project management. WRS, and WEM provided facilities/equipment and institutional liaisons. WRS and WEM provided consultation (including review of manuscript before submission). All authors read and approved the final manuscript.Submit your next manuscript to BioMed
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Clinical presentations, diagnosis, mortality and prognostic markers of tuberculous meningitis in Vietnamese children: a prospective descriptive study

Nguyen Duc Bang
Maxine Caws
Thai Thanh Truc
Tran Ngoc Duong
Nguyen Huy Dung
Dang Thi
Minh Ha
Guy E Thwaites
Doortje Heemskerk
Joel Tarning
Laura Merson
Pham Van Toi
Jeremy J Farrar
Marcel Wolbers
Thomas Pouplin
Jeremy N Day
Clinical presentations, diagnosis, mortality and prognostic markers of tuberculous meningitis in Vietnamese children: a prospective descriptive study
10.1186/s12879-016-1923-2R E S E A R C H A R T I C L E Open Access
Background: Tuberculous meningitis in adults is well characterized in Vietnam, but there are no data on the disease in children. We present a prospective descriptive study of Vietnamese children with TBM to define the presentation, course and characteristics associated with poor outcome.Methods: A prospective descriptive study of 100 consecutively admitted children with TBM at Pham Ngoc Thach Hospital, Ho Chi Minh City. Cox and logistic regression were used to identify factors associated with risk of death and a combined endpoint of death or disability at treatment completion.Results: The study enrolled from October 2009 to March 2011. Median age was 32.5 months; sex distribution was equal. Median duration of symptoms was 18.5 days and time from admission to treatment initiation was 11 days. Fifteen of 100 children died, 4 were lost to follow-up, and 27/81 (33 %) of survivors had intermediate or severe disability upon treatment completion. Microbiological confirmation of disease was made in 6 %. Baseline characteristics associated with death included convulsions (HR 3.46, 95CI 1.19-10.13, p = 0.02), decreased consciousness (HR 22.9, 95CI 3.01-174.3, p < 0.001), focal neurological deficits (HR 15.7, 95CI 1.67-2075, p = 0.01), Blantyre Coma Score (HR 3.75, 95CI 0.99-14.2, p < 0.001) and CSF protein, lactate and glucose levels. Neck stiffness, MRC grade (children aged >5 years) and hydrocephalus were also associated with the combined endpoint of death or disability. Conclusions: Tuberculous meningitis in Vietnamese children has significant mortality and morbidity. There is significant delay in diagnosis; interventions that increase the speed of diagnosis and treatment initiation are likely to improve outcomes.

Background

Tuberculosis (TB) is an important cause of childhood morbidity -recent estimates of the number of children developing TB each year range from 500 000 to 1 million, significantly higher than previously estimated by the WHO [1,2]. There may be 50 million children latently infected [3]. 5 % of disease occurs in HIV coinfected children, although this is higher in sub-Saharan Africa [3]. Despite this high burden, in TB as in many other diseases, children are a neglected group -the vast majority of data used to guide management are derived from adult patients.

Tuberculous meningitis (TBM) is the most severe form of tuberculosis, with high rates of disability and death [4]. Children are more likely than adults to develop disseminated TB and TB meningitis following infection [5]. This risk is greatest for infants and children under 2 years of age, probably due to the immaturity of the immune system [6]. The challenges of TBM diagnosis and management are exacerbated in children. Initial symptoms in infants are non-specific, it is difficult to obtain diagnostic samples and more invasive sampling methods are needed, and the diagnostics samples obtained generally proffer extremely low yields of mycobacteria [7,8]. Death from TBM is strongly associated with delays in diagnosis and treatment both in children and adults [9][10][11][12]. It is striking that there has never been a randomized controlled trial of anti-tuberculosis drugs in children with TBM [13].

Vietnam is classified as having a high burden of TB, with a prevalence in the order of 145 per 100 000 of the population as a whole [14]. Tuberculous meningitis in adults is well characterized in Vietnam, and these data have been key in developing treatment guidelines, but there are no data on the disease in children [11,[15][16][17]. In accordance with historic WHO policy, the Vietnamese National TB Programme has focused on the systematic notification of smear positive cases of TB. However, the majority of pediatric TB cases are smear negative, and subsequently limited data are available on pediatric TB in Vietnam. In line with WHO policy revisions, Vietnam has recently implemented disaggregated data collection for pediatric TB. Improving outcomes in children is dependent upon a better understanding of the epidemiology of childhood TB, and early diagnosis and instigation of effective treatment.

Methods

Study aim

This study aimed to describe the current practice in the management of Vietnamese children with TBM, the presenting clinical features and predictors of poor outcome (death and neurological disability), in order to define the challenges in management and prioritise research.

Study design

A prospective descriptive study of 100 consecutive cases of TBM in children (aged ≤15 years).

Setting and participants

The study was conducted at Pham Ngoc Thach Hospital (PNT), Ho Chi Minh City (HCMC). PNT is the tertiary referral centre for tuberculosis in the south of Vietnam, serving 40 million people. All children diagnosed or suspected of having TBM in HCMC and the surrounding provinces are referred here. Approximately 500 inpatient cases of pediatric TB are treated each year; around 20 % have meningitis.

Entry criteria

All patients aged ≤15 years presenting to Pham Ngoc Thach Hospital with a clinical syndrome consistent with TBM (meaning one or more of: fever, headache, neck stiffness, vomiting, confusion, coma, convulsions, cranial nerve palsies, hemiplegia or paraplegia) and considered to have tuberculous meningitis by their attending physician (i.e. meriting anti-TB therapy) were eligible to enter the study. TBM was classified as "definite", "probable" or "possible", as follows:

Definite TBM: acid-fast bacilli (AFB) seen or cultured from cerebrospinal fluid (CSF). Probable TBM: Clinical syndrome consistent with TBM, and one or more of the following criteria: suspected active pulmonary tuberculosis on chest radiography, AFB found in any specimen other than the CSF, brain imaging consistent with TBM, or clinical evidence of other extrapulmonary tuberculosis. Possible TBM: Clinical syndrome consistent with TBM and at least 4 of the following: past medical history of tuberculosis, predominance of lymphocytes in the CSF, illness of ≥6 days in duration, CSF: blood glucose ratio <0.5, altered consciousness, yellow CSF, and focal neurological signs.

Patient assessment

All patients had clinical assessments by the dedicated study team at study entry, 2 weeks, 1, 2, 3 and 8 months.

Lumbar puncture

All patients underwent lumbar puncture either at the referring centre or on admission to PNT hospital. Lumbar puncture was repeated at days 30 and 90 following study entry/treatment initiation. Cerebrospinal fluid (CSF) investigations included cell count, glucose, protein, lactate, Gram's stain, and India ink test, and culture for fungi and pyogenic bacteria. CSF Ziehl-Neelsen smear and culture were not available at referring centres. When patients were referred from other centres, lumbar puncture was only repeated at baseline if felt to be clinically indicated by the attending physician. The GeneXpert test was not available at the time the study took place.

Other investigations

All children had haematology and biochemistry investigations according to standard of care in the hospital. Sputum was examined for acid fast bacteria (AFB) when available; gastric washings for AFB were done at the discretion of the attending physician. All patients had HIV testing -counselling and HIV testing were available for the parents of children diagnosed with HIV. All patients had a chest radiograph performed at study entry. 40 patients were entered into a descriptive radiological substudy and underwent cranial Magnetic Resonance Imaging (MRI) at study entry, on day 60 and day 270. Other imaging was performed at the discretion of the attending physician.

Classification of severity

All patients were graded for severity at study entry. For children older than 5 years severity was graded according to a modified United Kingdom Medical Research Council criteria based on Glasgow Coma Score: Grade I had a Glasgow coma score (GCS) of 15/15 with no focal neurological signs, grade II either had a GCS 11-14 or GCS 15 with focal neurological signs, Grade III had a GCS of ≤ 10.

For children less than 5 years of age severity of TBM was graded according to the Blantyre Coma Score. Patients with grade I disease had a Blantyre coma score of 4-5 with no focal neurological signs; patients with grade II disease had a Blantyre coma score of 2-3 or a score of 4-5 with focal neurological signs; and grade III had a Blantyre coma score ≤1.

Treatment and follow-up

Anti-tuberculosis treatment was according to Vietnamese treatment guidelines, which at the time were consistent with the 2006 WHO guidelines. Patients received oral isoniazid (5 mg/kg), rifampicin (10 mg/kg), pyrazinamide (25 mg/kg), ethambutol 15 mg/kg and intramuscular streptomycin (15 mg/kg) for 2 months, followed by oral isoniazid, rifampicin, pyrazinamide and ethambutol for 1 month and oral isoniazid, rifampicin, and ethambutol at the same doses for 5 months [2HRZES/1HRZE/ 5HRE]. Streptomycin was not used for HIV-infected patients. Patients with MRC grades II and III and BCS grades II and III disease received adjuvant dexamethasone for the first six weeks; patients with MRC grade I and BCS grade I received adjuvant dexamethasone for 4 weeks as per Vietnamese guidelines [11]. All patients were reviewed daily by the study team while in-patients, at days 30, 60 and 90, and on completion of treatment after 8 months. DOT was used to secure and monitor treatment adherence, and drugs were administered via nasogastric tube to unconscious children.

Assessment of outcome

We were interested in two outcomes: survival, and a combined endpoint of neurological disability or death. Disability status was assessed at the end of 8 months of treatment with the use of the two simple questions ("Does the child require help from anybody for everyday activities [e.g., eating, drinking, washing, brushing teeth, and going to the toilet]?" and "Has the illness left the child with any other problems?") and the modified Rankin scale (scores range from 0 [no symptoms at all] to 6 [death]) and was classified as good (i.e., no disability), intermediate, severe, or death, as described elsewhere [11]. For children under 5 years, the response was determined by the study clinician in relation to the expected functioning in normal children of the same age.

Study size

The study was designed as a prospective descriptive study to include all patients less than or equal to 15 years of age presenting with suspected TBM to Pham Ngoc Thach Hospital. Approximately 100 such patients are admitted each year, and we planned to recruit 100 consecutively admitted patients.

Statistical analysis

The raw data was imported into a secure anonymised in-house data management system (CliRes). Between group comparisons of baseline characteristics were based on the Wilcoxon rank sum test and Fisher's exact test for continuous and categorical variables, respectively. Mortality at 8 months was estimated with the Kaplan-Meier method. Univariate Cox regression was used to identify significant factors influencing time to death. Factors relating to the probability of a combined endpoint of neurological sequelae (intermediate or severe disability) or death were determined using univariate logistic regression and the Firth correction was applied in case of separation [18]. Multivariable regression models were not fitted due to the relatively low number of events and large number of factors of interest. All analyses were performed using R software version 2.9.1 [19].

Results

Demographic and clinical characteristics

Enrollment was conducted between October 2009 and March 2011. During this period 133 children were admitted to PNT hospital with suspected TBM. Twelve children declined to join the study and 21 were not recruited because they were already receiving treatment.

Follow-up completed in December 2011. The median duration from first hospital admission to making the diagnosis of TBM (and instigation of treatment) was 11 days (range 1-74 days).

Baseline characteristics and outcomes for the cohort are shown in Table 1.

Fifty-six percent (n = 56/100) of patients were male. The majority of children (67 %) were less than 5 years old (median age 32.5 months, range 2 to 180 months). Four of 96 children tested were HIV infected (4 %); 5 % (n = 5/96) were hepatitis B surface antigen positive. Concomitant extra-pulmonary TB was common, seen in 42 patients (36 pulmonary, 4 pulmonary with peripheral lymphadenitis, 1 pulmonary disease with pleural involvement, and 1 pulmonary disease with concomitant TB arthritis. A family history of TB was reported for 27 patients (27 %); one patient had a previous history of TB.

Fever, vomiting and nuchal rigidity were the most frequently elicited symptoms. Seizures were common reported in 39 cases. Headaches occurred in at least 49 (49 %) cases -in 44 cases (44 %) the presence of headache was uncertain because the child was too young to describe the symptom. Of 33 (33 %) children  Table 1). Focal neurological signs were frequent occurring in 58 %, most commonly VIth cranial nerve palsies (22 %), followed by hemiplegia (20 %), VIIth cranial nerve palsy 7 %, paraplegia 6 %, monoparesis 4 %, IIIrd cranial nerve palsy 4 %, optic nerve atrophy 3 %, and quadriparesis 2 %. Four patients (4 %) were lost to follow up after 3 months of treatment.

Cerebrospinal fluid results

Lumbar puncture was performed on all patients (n = 100) at referring hospitals; 22 (22 %) children had repeat lumbar puncture at PNT. All CSF was analyzed for protein, lactate and glucose concentrations, and for cell count and differentials ( Table 2). The median white cell count was 202 cells/uL. 92 of 95 (97 %) patients had lymphocyte predominance (>50 %). The mean CSF:blood glucose ratio was 0.25 (range 0.07 to 0.69; 7 of 100 patients had ratios >0.5). 77 patients had CSF lactate measured; the median was 5.3 mmol/L (10th and 90 th centiles 2.36 and 8.8 mmol/L respectively). All but 8 patients had elevated CSF protein concentrations (median 1.2 g/L, upper limit of the normal range 0.4 g/L).

Microbiology results

None of 22 CSF samples taken at PNT were AFB smear positive, However, M. tuberculosis was cultured from 6 of these samples. Smears of sputum and gastric aspirates were positive for AFB in only 2 (7 %) of 29 patients and 5 (7 %) of 67 patients, respectively. Drug susceptibility testing was not performed.

TBM classification

Six cases met the definition of definite TBM. Sixty-six cases fulfilled the case definition of probable TBM: seven had positive AFB smears and/or M. tuberculosis cultured from sputum or gastric aspirate; 33 had abnormal chest X-rays consistent with TB and an abnormal brain imaging, and 26 cases had an abnormal CT or MRI brain imaging consistent with TBM. The remaining 28 cases fulfilled the definition of possible TBM, with clinical features and CSF biochemistry consistent with the diagnosis. The differences in baseline characteristics and outcome between definite/probable and possible cases are illustrated in Table 2. There were statistically significant lower rates of altered sensorium, neck stiffness and motor deficits at baseline, and a reduced risk of neurological sequelae in possible cases, suggesting that these patients may have had less severe disease.

Imaging findings

All children had chest X-ray examinations at admission: 42 % (42/100) had abnormalities consistent with TB (14 % mediastinal lymphadenopathy 14 %, consolidation 11 %, miliary pattern 9 %, nodules 6 %, cavity 1 % and atelectasis 1 %).

Forty-three patients underwent cranial MRI before beginning treatment (42 with contrast enhancement). Findings are shown in Table 3.

Baseline predictors associated with increased risk of death or neurological sequelae are shown in Table 4.

More severe BCS was predictive of increased risk of death, as were history of coma, fits, focal neurological deficits and CSF levels of protein, lactate and glucose. The study did not detect a statistically significant association between risk of death and MRC score but this may be due to the low number of children in the study aged ≥5 years. However, there was a consistent increase in the hazard of death as MRC grade worsened. Hydrocephalus, neck stiffness and MRC grade at baseline were associated with an increased risk of the combined endpoint of neurological sequelae or death (p = 0.01). Neither brain infarctions nor basal meningeal enhancement identified on brain imaging were associated with mortality or the combined endpoint. Two patients developed drug induced liver injury (DILI) according to the classification of antituberculosis drug-induced hepatotoxicity based on the WHO Adverse Drug Reaction Terminology [20]. This occurred at 2 and 4 weeks following treatment initiation. Neither case was infected with Hepatitis B or C virus. In both cases, PZA was discontinued completely and INH and RIF were reintroduced successfully. Both patients survived.

Uniform case definition for tuberculous meningitis

After this study was designed and recruited, a consensus document was published suggesting criteria to standardize the categorization of TB meningitis as possible, probable or definite, in order to allow comparison of different populations in intervention trials [21]. The criteria are based upon the expert opinion of a number of international experts. We reclassified our patients according to these new criteria, and this resulted in 18 cases moving from the 'probable' diagnosis to the new 'possible' category, and 8 cases moving from our 'possible' category to the new 'probable' category. Following re-categoristaion, male sex was no longer statistically significantly differently distributed between possible and probable/definite cases; altered sensorium, neck stiffness, motor deficit and permanent sequelae remained significantly more common amongst probable and definite cases. Cranial nerve palsies and death became significantly more associated with probable and definite cases.

Discussion

This study demonstrates the challenges in delivering effective treatment for TBM in children in Vietnam. First, TBM is associated with considerable mortality and morbidity, with a risk of death at the end of treatment of 15 %, and 33 % of survivors having intermediate or severe disability. These figures are similar to those reported from other studies in children, and to the rates of death and disability seen in HIV uninfected adults with TBM in Vietnam, but while in adult disease considerable progress has been made and large studies are on-going, childhood TBM remains a neglected area [11,13,[22][23][24][25][26][27][28][29]. Treatment guidelines for children are largely derived from studies in adults, and although efforts are underway to develop pediatric formulations in appropriate ratios, at the present time dosing schedules are limited by adult fixed dose combination tablets. Randomised controlled trials and pharmacokinetic studies of novel dosing strategies and agents in children are needed to ensure treatment is optimized.

Secondly, the timely instigation of treatment in TBM remains a significant challenge, even in countries such as Vietnam where the burden of TB is high and the diagnosis is at the forefront of clinicians' minds. In this study, the median time from presentation to treatment was 19 days, and 50 % of deaths occurred within the first 6 days of treatment. Earlier instigation of treatment may be able to prevent these deaths. Delays in diagnosis and treatment are likely explained by 3 main factors. First, poverty is a barrier to accessing health care. Since the study Vietnam has made important progress in rolling out free access to healthcare for children under the age of 6 years; however, this is beyond the means of many countries where the TB burden is highest. Secondly, TBM presents in a non-specific manner and it is rare to confirm the diagnosis microbiologically even in high resource settings. In this study, a definitive diagnosis was made in only 6 % of cases. This is partly explained because only 22 % (22/100) of patients had a CSF smear and culture, although the study is representative of real world practice. Of note, no patients were CSF smear positive. Most papers report finding AFB in fewer than 20 % of TBM patients [30]. Improving laboratory training and infrastructure, and improving access to WHO endorsed technologies such as the GeneXpert, would potentially reduce this delay but will not alter the fact that clinical specimens from children are limited both by their volume and their paucibacillary nature [31]. An adequate volume of CSF significantly affects the likelihood of confirming the diagnosis [32] and appropriate sampling for TB at other sites should be performed. Moreover, while TB diagnostic tests remain poorly sensitive, increasing the capacity to identify and exclude other central nervous system pathogens is key in giving clinicians the confidence to instigate treatment in a timely manner and will reduce unnecessary prescription of lengthy TB regimens. Of note, an approach that has shown promise in South African children with TBM, which resulted in a doubling of diagnostic sensitivity, is  the use of more than one nucleic acid amplification test on CSF [33]. However, the investigators still found a combination of microscopy and culture to be most effective. We have found GeneXPert and CSF smear to have similar sensitivities of in adult patients; the challenge for Vietnam remains in obtaining significant volumes of CSF from infants and balancing the risk of investigation with the benefits of a definitive diagnosis [31]. The early identification of drug resistance is likely to be an important factor in improving outcomes. A South African study found that drug resistance was associated with delays in instigation of effective treatment, and that multidrug resistance was associated with worse outcomes [34]. In this study isoniazid mono-resistance was not clearly associated with worse outcomes [34]. However, this mimics the experience in adult patientsinitial small studies failed to show a deleterious effect of isoniazid mono-resistance on outcome, but later larger datasets demonstrated that indeed such resistance is disadvantageous [35,36]. Thirdly, TB treatment is onerous, both in regards to side effects and duration, which may lead to reluctance to start empirical treatment where the risk and consequences of disease are perceived to be low. However, M. tuberculosis has been reported to be a more frequent cause of meningitis than pyogenic organisms in South Africagiven that 50 % of deaths are occurring within the first week of treatment a case could be made for early empirical TB treatment in such centres [37]. Few data exist on the optimal duration of treatment for TBM. Drugs such as the fluoroquinolones, which have good tolerability and excellent CSF penetration, potentially offer more effective and palatable treatment regimens, but are relatively untested in children [38]. Randomized controlled trials in children specifically designed to improve TB treatment by 1) identifying shorter equally effective courses and 2) new treatment combinations, may go some way to addressing this issue, although recent trials in adult patients have had mixed results [39][40][41][42]. The effective dose of rifampicin appears to be key in improving outcomes. Such regimes would enable a move towards an empirical therapeutic approach similar to that used in acute bacterial meningitis to be employed in high burden settings.

Finally, it is reassuring that drug induced liver injury necessitating treatment interruption was rare and not associated with a poor outcome in this study, affecting just 2 % of the patients. Our study is small and thus our estimates are somewhat imprecise. However, the rate is considerably lower than the 13 % quoted for DILI in adults, supporting the concept that higher doses could be used in children, as advocated in the recent WHO guidelines. [2,[43][44][45].

Our study had some limitations. It was limited by its small size, and thus estimates around the rates of death and other sequelae lack precision, although findings are generally in keeping with other series [13]. Secondly, we used all-cause mortality. However, 50 % of all deaths occurred within 1 week of treatment initiation, and the rates of co-morbidities (such as HIV) were low, meaning that it is reasonable to assume that all deaths were either a direct consequence of TB or a result of its sequelae. Thirdly, children were only followed up until the end of treatment, and we may have missed later deaths and relapse. The main limitation is the low rate of microbiological confirmation of tuberculosis. This is consistent with other studies in children and represents the very real practical difficulties of managing these children. It is possible that some of these cases, particularly those meeting the 'possible' case definition, may have had some other pathology. However, when the possible cases are excluded, then the mortality and morbidity rate rises further underlying the need to improve diagnostics and treatment for this devastating disease.

Our study was designed and completed before the publication of the universal case definition (UCD) for TBM was published and thus we present our results as originally intended, with a secondary analysis using this classification [21]. The UCD is based upon a non-linear scoring system derived from expert opinion, and has been shown to misclassify 14 % of cases of culture proven TBM as possible TBM in children in a South African study [46]. This underlines the danger of using this research tool as a diagnostic aid, particularly where microbiological diagnostic facilities are poorly developed. Moreover, it is not yet clear that the UCD achieves that which it set out to achievei.e allowing robust comparison of patients across diverse study groups according to the UCD defined likelihood of there being definite, probable or possible TBM. As an illustration, a study from South Africa found that patients with 'possible' versus other 'probable/definite' TBM had significant differences in CSF protein concentrations and CSF/serum glucose concentrations. This difference was not apparent in our children, suggesting that our 'possible' cases may be more likely to actually have TBM than possible cases from South African series [47]. There is a need to develop more robust data-driven classification systems, and given the number of patients enrolled into intervention trials in the last 15 years this should be feasible [11,15,38,48].

Conclusions

Tuberculous meningitis in children carries significant morbidity and mortality in Vietnam. A particular challenge is in reducing the time to diagnosis, and institution of effective treatment. However, improving outcomes will also require the development of treatment regimens tailored to children. Given the recent disappointing results of fluoroquinolone boosted treatment regimens in adults with TBM, randomized controlled trials of boosted rifampicin dosing would seem the most important strategy to develop.

≥ 5 years of age, 16 (48 %) had MRC grade I disease, 11 (33 %) grade II disease, and 6 (18 %) grade III disease. The remaining 67 children under 5 years were graded using the Blantyre coma score (BCS): BCS I

were frequent, detected in 86 % of patients: 62 % (26/42) had basal meningeal enhancement, 44 % (19/43) hydrocephalus, 30 % (13/43) infarctions and 14 % (6/42) tuberculomas. 35 of these 43 patients had repeat cranial MRI scans performed 60 days post randomization: 37 % (13/35) had basal meningeal enhancement, 29 % (10/35) hydrocephalus, 34 % (12/35) infarctions and 29 % (10/35) tuberculomas. Death and sequelae Fifteen patients died by 8 months (Kaplan-Meier estimate of mortality 15.7 %, 95CI: 9.56-24.3 %, 4 patients lost to follow-up). Eight (53 %) deaths occurred within the first 6 days of treatment; 14 within 45 days of diagnosis. At the end of treatment, six of 81 surviving patients (7.4 %) were classified with severe disability and 21/81 (26 %) were classified with intermediate disability

Abbreviations AFB: Acid fast bacilli; BCS: Blantyre coma score; CSF: Cerebrospinal fluid; DILI: Drug induced liver injury; DOT: Directly observed treatment; E: Ethambutol; GCS: Glasgow coma score; H: Isoniazid; HCMC: Ho Chi Minh City; HIV: Human immunodeficiency virus; INH: Isoniazid; MRC: Medical Research Council; MRI: Magnetic Resonance Imaging; PNT: Pham Ngoc Thach Hospital; PZA: Pyrazinamide; R: Rifampicin; RIF: Rifampicin; S: Streptomycin; TB: Tuberculosis; TB: Tuberculosis; TBM: Tuberculous meningitis; UK: United Kingdom; WHO: Word Health Organisation; Z: Isoniazid

Table 1
1Baseline characteristics and outcomes of 100 childhood TBM patientsSymptoms and
signs

Number affected (%)
Median duration in
days (range)

Fever
96/97 (99 %)
23; (6-96)

Vomiting
76/100 (76 %)
13; (1-96)

Weight loss
59/98 (60 %)
15.5; (7-90)

Confusion
15/100 (15 %)
10.4; (2-30)

Unconsciousness 27/100 (27 %)
5.3; (1-16)

Headache a
49/55 (89 %)
21; (4-66)

Fits
39/100 (39 %)
8.5; (1-35)

Neck stiffness
75/100 (75 %)

Hemiparesis/
Hemiplegia

20/98 (20 %)

Paraparesis/
paraplegia

6/98 (6 %)

Monoplegia
4/98 (4 %)

Quadriplegia
2/98 (2 %)

II nerve
involvement

3/98 (3 %)

III nerve palsy
4/98 (4 %)

VI nerve palsy
20/98 (20 %)

VII nerve palsy
7/98 (7 %)

Anemia
(Hb < 11 g/dL)

46/99 (46 %)

HIV infection
4/96 (4 %)

HBV infection
5/96 (5 %)

MRC Grades
>5 years (33)

I: 16 (48 %)
II: 11 (33 %)
III: 6 (18 %)

Blantyre <
5 years (67)

4-5: 43 (64 %) 2-3: 12 (18 %) 0-1: 12 (18 %)

Deaths
15/100 (15 %)

Sequelae

Severe
6/81 (7 %)

Intermediate
21/81 (26 %)

a

Unable to ascertain in 44 due to the age of the child; headache was not
assessed for one additional subject

Table 2
2Baseline characteristics of possible TBM and definite/probable TBMVariables
Possible TBM (n = 28)
Definite/Probable TBM (n = 72)
P-value for comparison

Age a (months)
24.5 (2-165)
36.5 (2-180)
0.09

Male (%)
18/28 (64 %)
38/72 (53 %)
0.03

Fever
28/28 (100 %)
71/72 (99 %)
0.99

Symptom duration a (days)
16 (6-60)
19.5 (6-96)
0.172

Vomiting
20/28 (71 %)
56/72 (78 %)
0.50

Altered sensorium
6/28 (21 %)
36/72 (50 %)
0.01

Fits
9/28 (32 %)
30/72 (40 %)
0.38

Neck stiffness
17/28 (61 %)
58/72 (81 %)
0.04

Motor deficit
4/25 (16 %)
28/60 (47 %)
0.01

Cranial nerve palsy
9/28 (32 %)
18/72 (25 %)
0.91

HIV infection
1/28 (4 %)
3/72 (4 %)
0.99

HBV infection
2/28 (7 %)
3/72 (4 %)
0.86

Family TB history
7/28 (25 %)
19/72 (26 %)
0.89

Death
2/27 b (7 %)
13/69 (19 %) c
0.28

Permanent sequelae
2/25 (8 %)
25/56 (45 %)
0.002

CSF WCC a (cells/uL)
144 (4-780)
150 (1-802)
0.37

CSF Lymph a (cells/uL)
80 (40-100)
80 % (50-100)
0.44

CSF Protein a (g/L)
0.8 (0.2-5)
1.3 (0.1-4.8)
0.08

CSF Lactate a (mmol/L)
4.3 (1.4-8.8)
5.6 (1.21-19.2)
0.08

CSF: Blood Glucose ratio a
0.30 (0.09-0.61)
0.25 (0.07-0.69)
0.51

a Values are medians/ranges

b

1 lost to follow-up

c

3 lost to follow-up

Table 3
3Baseline brain MRI scan results for 43 patientsFinding
Absolute frequency (%)

Any abnormality
37/43 (86 %)

Meningeal enhancement
26/42 (62 %)

Basal
25 (60 %)

Sylvian Fissure
16 (37 %)

Suprasellar cistern
4 (9 %)

Hydrocephalus
19/43 (44 %)

Tuberculoma
6/42 (14 %)

Infarction
13/43 (30 %)

Basal Ganglia
8/43 (19 %)

Cerebral cortex
3/43 (7 %)

Internal capsule
1/43 (2 %)

Brain stem
1/43 (2 %)

Table 4
4Univariate analysis of potential predictors of mortality and neurological sequelae in patients with tuberculous meningitisCharacteristic
Time to death (N = 100)
Neurological sequelae or death (N = 96)

Death/No at risk
HR (95 % CI)
P
Events/No at risk
OR (95 % CI)
P

Sex

a

Male
10/56 (17.9 %)
0.61
0.36
23/54 (42.6 %)
1.11
0.80

Female
5/44 (11.4 %)
(0.21-1.78)
19/42 (45.2 %)
(0.49-2.52)

Age

a

<5 years
11/67 (16.5 %)
0.70
0.54
30/64 (46.9 %)
0.68
0.38

≥ 5 years
4/33 (12.1 %)
(0.22-2.20)
12/32 (37.5 %)
(0.28-1.61)

Duration of symptoms N = 89
1.00
0.4
-
1.01
0.43

(per +1 day)
(0.98-1.01)
(0.98-1.04)

Neck stiffness

a

No
1/25 (4.0 %)
5.15
0.11
5/24 (20.8 %)
4.02
0.01

Yes
14/75 (18.7 %)
(0.68-39.16)
37/72 (51.4 %)
(1.44-13.18)

HIV co-infection

a

No
13/92 (14.1 %)
1.85
0.55
39/88 (44.3 %)
0.42
0.43

Yes
1/4 (25.0 %)
(0.24-14.17)
1/4 (25.0 %)
(0.02-3.42)

BCS Grade

age <5 years

a

BI
0/43 (0 %)
1.00
<0.001
10/40 (25.0 %)
1.00
<0.001

BII
3/12 (25.0 %)
27.96 b
9/12 (75.0 %)
9.00

(2.71-3760)
(2.21-47.06)

BIII
8/12 (67.0 %)
94.64 b
11/12 (91.7 %)
33.00

(11.71-12,260)
(5.44-643.12)

TBM grade

(age ≥ 5 years)

a

I
1/16 (6.3 %)
1.00
0.28
2/15 (13.3 %)
1.00
0.01

II
1/11 (9.1 %)
1.41
5/11 (45.5 %)
5.41

(0.09-22.5)
(0.81-36)

III
2/6 (33.3 %)
6.26
5/6 (83.3 %)
32.5

(0.57-69.2)
(2.4-443)

Convulsions

a

No
5/61 (8.2 %)
3.46
0.02
20/59 (33.9 %)
2.86
0.01

Yes
10/39 (25.6 %)
(1.18-10.13)
22/37 (59.5 %)
(1.24-6.81)

Decreased level of consciousness

a

No
1/58 (1.7 %)
22.9
<0.001
10/54 (18.5 %)
14.08
<0.001

Yes
14/42 (33.3 %)
(3.01-174.3)
32/42 (76.2 %)
(5.46-39.85)

Focal neurological deficits

a

No
0/53 (0 %)
15.66
0.01
6/50 (12.0 %)
15.4
<0.001

Yes
4/32 (12.5 %)
(1.67-2075)
21/31 (67.7 %)
(5.22-51.96)

Extra meningeal TB

a

No
6/51 (11.8 %)
2.3
0.11
19/57 (33.3 %)
2.87
0.01

Yes
9/30 (30.0 %)
(0.82-6.45)
23/39 (59.0 %)
(1.25-6.80)

TB culture

a

Negative
2/14 (14.3 %)
2.72
0.33
4/16 (25.0 %)
4.50
0.16

Table 4
4Univariate analysis of potential predictors of mortality and neurological sequelae in patients with tuberculous meningitis (Continued) Baseline category. HR and OR give comparisons to the baseline category. P-value is an overall likelihood ratio test for the significance of the factor b Model fitted by logistic regression with Firth correction c hydrocephalus diagnosed by MRI brain (43 patients or CT brain 19 patients)Positive
2/3 (66.7 %)
(0.38-19.4)
3/5 (60.0 %)
(0.56-45.4)

Hydrocephalus c

a

No
2/31 (6.5 %)
3.46
0.10
6/31 (19.4 %)
9.72
<0.001

Yes
6/30 (20.0 %)
(0.70-17.16)
21/30 (70.0 %)
(2.97-32)

Cranial nerve palsy

No
14/70 (20.0 %)
5.42
0.10
29/70 (41.4 %)
0.71
0.45

Yes
1/26 (3.8 %)
(0.71-42.2)
13/26 (50.0 %)
(0.29-1.75)

CSF Protein
N = 99
1.74
0.002
N = 94
1.65
0.01

(per + 1 g/L)
(1.22-2.49)
(1.14-2.51)

CSF Lactate
N = 77
1.14
0.04
N = 73
1.20
0.03

(per + 1 mmol/L)
(1.01-1.29)
(1.01-1.47)

CSF Glucose
N = 100
0.45
0.05
N = 96
0.65
0.10

(per + 1 mmol/L)
(0.20-0.98)
(0.38-1.08)

a

AcknowledgementsWe thank the study participants, their parents, and the ward, administrative and laboratory staff of PNT, and the funders for making this study possible.FundingFunded by the Wellcome Trust UK. JND is a Wellcome Trust Intermediate Fellow Grant No WT097147MA.Availability of data and materialsThe ethical approval and consent procedures did not include permission to make the raw data available for public dissemination since this was not practice at the time of the study.Authors' contributions JND, TP, NDB and JF designed the study; NDB, JND, TND, NHD, PVT, DTMH, MC, LM and TP generated the data; NDB, JND, TTT and MW analysed the results; JND wrote the first draft of the manuscript; all authors reviewed and edited the manuscript. All authors read and approved the final manuscript.Competing interestsThe authors declare that they have no competing interests.Ethics approval and consent to participateThe study received ethical approval from the ethical review board of Pham Ngoc Thach Hospital, Viet Nam, the Health Services of Ho Chi Minh City and the Oxford University Tropical Ethics Committee, UK. Written informed consent was obtained from the parents or guardians of all participants, and assent from all children with capacity. Submit your next manuscript to BioMed Central and we will help you at every step:
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