Somatosensory evoked potentials in amyotrophic lateral sclerosis.

Abstract

SUMMARY Forty five patients with amyotrophic lateral sclerosis were investigated, by means of somatosensory evoked potentials, in order to detect the presence of subclinical sensory changes. Cervical SEPs from the median nerve and cortical SEPs from the median and tibial nerve were recorded, showing a delay of N1B and subsequent components; the latency of the first constant cortical potential was also increased in many patients. Only the SEPs from the tibial nerve showed a decrease of amplitude. These results suggest a pathological slowing of conduction along the central sensory pathways in amyotrophic lateral sclerosis.Amyotrophic lateral sclerosis is generally considered to be a system disease because of selective involvement of upper and lower motor neurons. Sensory disturbances characteristically are absent in typical amyotrophic lateral sclerosis, although cramps and paraesthesias may occur; nevertheless a certain number of detailed pathological studies have claimed to show the presence of changes in sensory nerve myelinated fibres,' 2 in spinocerebellar pathways,3 Clarke's nucleus,4 posterior columns5 ' and thalamus.8 These changes have been reported more frequently in familial than in sporadic amyotrophic lateral sclerosis.9 A patient with a chronic pain syndrome associated with amyotrophic lateral sclerosis has recently been described.'0 In a series of investigations about the possible involvement of subsystems other than motor neurons in sporadic amyotrophic lateral sclerosis, we have examined somatosensory evoked potentials (SEPs) in 45 patients in an attempt to detect the presence of subclinical alterations. The clinical picture of these patients were divided into: typical amyotrophic lateral sclerosis without bulbar signs, typical amyotrophic lateral sclerosis with bulbar signs, bulbar and pseudobulbar amyotrophic lateral sclerosis and amyotrophic lateral sclerosis with predominant lower motor neuron involvement (without pyramidal signs). The patients were further divided into three groups, according to the duration of the disease: I = up to 12 months, II = from 13 to 24 months, III = more than 24 months. The muscular impairment was classified as light, moderate or heavy, according to the clinical evaluation of the functional capacity. The tallness of the patients and the presence or the absence of cervical spondylosis on plain radiographs was also considered. These clinical features are shown in table 1.The control cases, matched for age, sex and tallness were sampled from normal subjects of the laboratory. The patients, relaxed in an arm-chair, in a silent room, were requested to close their eyes. The stimulating electrodes were placed on the skin overlying the median nerve at the wrist and the tibial posterior nerve at the ankle; both sides were sometimes examined. The stimulus had a duration of 0-1 ms, a frequency of 3 Hz and an intensity of 20% above that required to induce a modest muscular twitch. The recording silver-silver chloride electrodes were placed at C3 or at C4-Fpz (cortical SEPs aft...

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