Sensorimotor polyneuropathy in patients with SMA type-1: electroneuromyographic findings.

Introduction: Generally, spinal muscular atrophy (SMA) is believed to be a pure motor neuron disease. We retrospectively evaluated our electrodiagnostic findings in SMA type 1 patients to demonstrate co-existence of sensorimotor neuropathies.

Methods: Electroneuromyographic (ENMG) studies in 15 patients (11 boys, 4 girls) were reviewed independently by 2 neurophysiologists. Upper extremity findings were compared with normal right arm controls.

Results: Patient ages ranged from 1.5 to 26 months. Four SMA patients (26.7%) had decreased sensory nerve action potentials (SNAPs) or sensory nerve conduction velocities. Of them, median SNAPs could not be elicited in 3, and sural SNAPs could not be elicited in 2. Compound muscle action potential amplitudes were severely decreased in 14 (93.3%) and normal in 1.

Conclusions: Survival motor neuron 1 (SMN1) gene analysis should be considered if clinical features are consistent with SMA, even if pathological or electrophysiological findings demonstrate peripheral sensorimotor polyneuropathies.