PMC5960698_01
(A) Videonystagmographic trace with the patient looking at a fixed central target straight ahead in the light, with the head free taken on Day 13 from symptom onset. Note the sinusoidal eye oscillations representing a compensatory movement to the head oscillations (i.e., a sinusoidal vestibulo-ocular reflex). There is no clear nystagmus evident on the trace (nor on clinical examination). (B) Videonystagmographic trace showing periodic alternating nystagmus on day 21 from symptom onset: left-beating predominantly horizontal nystagmus, a null period with no horizontal nystagmus, but prominent vertical (upbeat) nystagmus, followed by a reversal of the horizontal nystagmus into right-beating, with some attenuation of the vertical nystagmus. In central gaze, the left-beating nystagmus peak slow phase eye movement velocity (SPV) was 22 /s, and right-beating SPV was 34 /s. There was upbeat nystagmus starting 5 s prior to the change in nystagmus direction, with a SPV of 10 /s. Upward deflection represents rightward (for horizontal trace), and upward (for vertical trace) eye movements. (C) A 70 s videonystagmographic recording of the horizontal eye movements showing a longer period of alternating nystagmus with the eyes in the primary position, without fixation. (D) Electronystagmographic recordings in central gaze in the light (with fixation) and the dark (without fixation). Note the mostly linear or decreasing exponential velocity waveform of the nystagmus slow phase [insets in parts (C,D)] that is more suggestive of an acquired nystagmus. Indeed, no clear congenital-type waveforms were seen in the traces.
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F1
Ten days after the original assessment the head movements worsened dramatically, rendering interpretation of the eye movements difficult (Figure 1A; Video S3 in Supplementary Material), but the patient continued to complain of oscillopsia, even when the examiner attempted to restrain the head manually (the patient did not consent to the use of a bite bar). With the head now still it became possible to visualize the eye movements revealing periodic alternating nystagmus (PAN) with a cycle of approximately 90 s, and a null phase of 2 s (Figures 1B,C; Video S4 in Supplementary Material).
(A) Sagittal cross-sectional T1-weighted magnetic resonance image showing atrophy of the superior cerebellar peduncles, and anterior aspects of the cerebellum (white arrow) involving the uvula and nodulus. (B) Coronal T2-weighted magnetic resonance image showing bilateral atrophy of the anterior cerebellum, including the nodulus and uvula, and superior cerebellar peduncles with associated high signal (gliotic) change. (C) Axial T2-weighted magnetic resonance image showing atrophy of the nodulus (black arrow) within the enlarged fourth ventricle. (D) Axial T2-weighted magnetic resonance image showing nodulus (black arrow) and fourth ventricle in a healthy age-matched control. Note the flattening of the nodulus and expansion of the fourth ventricle in (C).
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F2
An MRI brain scan on day 6 showed bilateral symmetrical superior cerebellar peduncle atrophy, thinning of the anterior cerebellar structures, and enlargement of the fourth ventricle (Figure 2), unchanged at 6-month follow-up.