Clinical and electrophysiological features of acute flaccid myelitis: A national cohort study

OBJECTIVE: To summarize the neurophysiological properties of acute flaccid myelitis (AFM) and evaluate limb-based motor outcomes. METHODS: Nerve conduction studies (NCS) in 49 patients (21 females, 28 males; median age = 52 m) with AFM (median = 7 d after onset; range 1-122 d) were reviewed. Neurophysiological findings, together with treatment and prognosis, and neurophysiology-neuroimaging correlations were analyzed. RESULTS: The findings indicated that 64% of paralytic limbs during the acute stage (≤14 d after onset) showed diminished or absent compound muscle action potentials (CMAPs), 79% showed normal motor nerve conduction velocities, 55% showed decreased persistence or absent F-waves, and 95% showed normal sensory nerve conduction velocities. The rate of CMAP abnormalities increased from 41% on days 1-2 to 83% on days 13-14. The reduction in CMAP amplitude was correlated with weaker muscle strength at both the peak neurological deficit and the last follow-up. The baseline limb-based muscle strength at nadir and anterior horn-localized magnetic resonance imaging lesions at recovery stage (>14 d) were strong predictors of outcome at the last follow-up. CONCLUSIONS: AFM typically shows neurophysiological features of neuronopathy. SIGNIFICANCE: NCS is probably useful in the diagnosis and evaluation of AFM.