Acute onset of infantile spinal muscular atrophy

Age-related sensory neuropathy in patients with spinal muscular atrophy type 1

INTRODUCTION/AIMS

Spinal muscular atrophy type 1 (SMA 1) is a devastating motor neuron disorder that leads to progressive muscle weakness, respiratory failure and premature death. Although sensory electrophysiological changes have been anecdotally found in pediatric SMA 1 patients, the age of onset of sensory neuropathy remains unknown.

METHODS

Sensory nerve conduction studies of the median and sural nerves were performed in 28 consecutive SMA 1 patients of different ages. Sensory nerve conduction velocities and sensory nerve action potential (SNAP) amplitudes recorded in these patients were compared with those obtained from 93 healthy subjects stratified by age.

RESULTS

SNAP amplitudes decreased with increasing age in the sural and median nerves, without any significant difference between upper and lower limbs.

DISCUSSION

Our data suggest that sural and median nerve SNAP amplitudes are normal in younger patients, while an axonal neuropathy appears in older ones.

Type I spinal muscular atrophy can mimic sensory-motor axonal neuropathy

Spinal muscular atrophy is a group of allelic autosomal recessive disorders characterized by progressive motoneuron loss, symmetric weakness, and skeletal muscle atrophy. It is traditionally considered a pure lower motoneuron disorder, for which a current definitive diagnosis is now possible by molecular genetic testing. We report two newborns with a clinical phenotype consistent with that of spinal muscular atrophy type I and nerve conduction studies and electromyography suggesting more extensive sensory involvement than classically described with spinal muscular atrophy. Molecular testing confirmed spinal muscular atrophy in patient 1 but not in patient 2. Thus, in the setting of a suspected congenital axonal neuropathy, molecular testing might be necessary to distinguish spinal muscular atrophy type I from infantile polyneuropathy.