PMC5491821_01
The percent decrease in the compound motor action potential (CMAP) between the Erb point and the stimulation of the axilla in the bilateral median nerves and ulnar nerves. Nerve conduction study (NCS) examinations were performed at 4, 9, 40, 61, and 100 days from the onset of disease. The bold and underlined values are interpreted as a conduction block (>50% decrease in CMAP) and conduction slowing, respectively.
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The results of conventional NCS at 4 days from the onset of symptoms showed the prolongation of distal motor latencies (DMLs) in the left ulnar nerve (5.0 ms) and right median nerve (4.0 ms), the prolongation of F-wave latencies in the bilateral median (28.9/28.3 ms) and ulnar nerves (30.4/30.7 ms), conduction block at the left cubital tunnel [motor conduction velocity (MCV) was 38 m/sec], and a suspected conduction block with bilateral decreases (48% in right, 50% in left) of the compound motor action potential (CMAP) between the Erb point and the axilla (Table and Fig. 1). MRN of the neck at 5 days from the onset of symptoms showed no diagnostic findings (Fig. 1). F-wave latency in each nerve (Table and Fig. 1). Follow-up sequential NUS showed the ultrasonographic enlargement of all of the cervical spinal nerves, which tended to be maintained until 2 months after the onset of the disease.
The cervical spinal nerve diameters measured by nerve ultrasonography (NUS). A is for the right side, while B is for the left. NUS examinations were performed at 5, 9, 40, 61, and 100 days from the onset of disease. C5 stands for the 5th cervical spinal nerve; the other nerves are similarly labeled. The bold and underlined values are higher than the mean values in healthy Japanese adults.
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The results of NUS at 5 days from the onset of symptoms showed the enlargement of bilateral 5th, 6th, and 7th cervical spinal nerves (3.8 mm and 3.1 mm in diameter at the right and left 5th cervical spinal nerves, 3.7 and 4.1 mm at the 6th, and 3.9 and 4.1 mm at the 7th) (Fig. 2). The abnormalities then gradually recovered in the chronic phase (Fig. 2).
The MR neurography images at 5 days (A, B) and 60 days from the onset of disease (C, D). The coronal short-tau inversion recovery (STIR) source image shows the almost symmetrical mild hyperintensity of each cervical nerve in the acute phase (A), and no significant change in comparison to the chronic phase (C). The post-processed STIR images with maximum intensity projection (MIP) reconstruction in the acute (B) phase and those in the chronic phase (D) are also shown. Right, the 6th spinal nerve seemed to be mildly enlarged, but not changed from the acute phase to the chronic phase (arrow).
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Follow-up MRN showed no apparent change (Fig. 3).