Motor nerve conduction study and muscle strength in newly diagnosed POEMS syndrome

Mixed demyelination and axonal loss are electrophysiological features of polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes (POEMS) syndrome. It is unclear whether the demyelination and axonal loss occur concurrently.

Electromyography was performed in 37 patients with newly diagnosed POEMS syndrome. Compound muscle action potential (CMAP) amplitude, distal motor latency, motor conduction velocity (MCV), and spontaneous activity were collected. Muscle strength was measured according to the Medical Research Council (MRC) scale.

MCV decreased in all nerves with decreased CMAP amplitude and in 93% of nerves with normal amplitude. CMAP amplitude decreased in 54% of nerves with decreased MCV and was normal in all nerves with normal MCV. MCV deceased in 95% of nerves with normal MRC. Abnormal spontaneous activity was detected in 32% of upper limb muscles.

Demyelination may be the main manifestation in POEMS neuropathy at an early stage, and axonal loss may be secondary to demyelination as the disease progresses.