Evoked potentials in spinal muscular atrophy.

Visual evoked potentials, brainstem evoked responses, and somatosensory evoked potentials were evaluated in 22 children with spinal muscular atrophy, types I and II. Eleven of the children had the severe form of spinal muscular atrophy (type I) and 11 children had the intermediate form (type II). The results of visual evoked potentials, brainstem evoked responses, and somatosensory evoked potentials were compared with those obtained in a control group. Statistical analysis showed abnormalities in the different sensory modalities. A significant increase in the visual evoked potential latencies was observed and was found more often in patients with spinal muscular atrophy type I. Alterations of the somatosensory thalamocortical responses were also observed, as well as a delay in the central conduction time. Although spinal muscular atrophy is usually considered to be a purely motor disorder involving neurons of the spinal anterior horn and nuclei of the lower cranial nerves, lesions of the posterior roots, spinal ganglia, ascending tracts, lateral geniculated corpus, and thalamus have been reported. Our results suggest that sensory neuron degeneration occurs more commonly in spinal muscular atrophy than previously thought and that this process probably develops more slowly than motoneuron degeneration. Such degeneration may be associated with brain atrophy.