The contribution of evoked potentials in the functional assessment of the somatosensory pathway

The value of evoked potentials in studying conduction in the somatosensory pathway was assessed in patients with various neurological disorders. In patients with multiple sclerosis (MS) abnormalities of the cervical response (N14) were found particularly in longstanding cases but also in the early stages of the disease, even in patients without sensory symptoms or signs, and were reversible in some patients. The cortical response was also abnormal in some cases but the two were not always affected together. In Friedreich's ataxia both the cervical and cortical responses were usually abnormal. Subclinical abnormalities of the cervical responses were found in some patients with hereditary spastic paraparesis or mixed forms of spinocerebellar ataxia. The cervical responses were also abnormal in patients with peripheral neuropathy and cervical radiculopathy, and in some patients with brain-stem or thalamic lesions. Cervical and cortical responses were normal in the lateral medullary syndrome, whereas the cortical response was markedly abnormal in patients with high brain-stem or cerebral hemisphere vascular lesions. Cortical and subcortical responses were abnormal in some patients with stereotactic thalamic lesions. Enhanced cortical responses were found in patients with lesions at different levels in the CNS. The most marked enhancement was observed in patients with familial myoclonic epilepsy. Lesser degrees were found in some patients with MS, progressive supranuclear palsy, thalamic lesions, brain-stem encephalitis and syringomyelia. Enhanced responses were usually found in patients with minimal or no clinical sensory involvement. It is postulated that this type of abnormality results from an interference to the inhibitory mechanisms which normally operate at various levels in the somatosensory pathway. It is concluded that evoked potential studies are a valuable adjunct to the clinical evaluation of sensation, and that they may provide useful information on the pathophysiology of conduction in the somatosensory pathway.