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During a field study in the Seychelles Islands, 19 patients with tropical spastic paraparesis (TSP) were evaluated electrophysiologically. Methods of assessment included motor and sensory nerve conduction studies, electromyography, and analysis of the somatosensory evoked potentials after stimulation of the tibial and median nerves. The results showed that the most prominent feature of the disease, a spastic paraparesis, is accompanied by subclinical involvement of spinal sensory pathways and a comparatively minor peripheral sensorimotor polyneuropathy.

The central conduction time of the descending and ascending fibers of the spinal cord were examined in patients with radiologically defined cervical spinal stenosis (antero-posterior diameter of the spinal canal less than 13 mm). Nineteen patients were examined, only 4 of whom showed clinical signs of spastic weakness or ataxia. The electromyographic response after non-invasive stimulation of the leg area of the motor cortex was delayed in 13 of the 15 clinically unaffected patients. The central latency (N21-P39) of the somatosensory evoked response after stimulation of the tibial nerve (tibialis SEP) was increased in 12 of the 15 individuals. The 4 patients with clinical signs showed abnormal latencies with both methods. The use of both techniques for the examination of the function of the spinal cord revealed increased latencies in the central motor and/or sensory pathways in all patients. The technique of non-invasive stimulation of the corticospinal system therefore provides an additional tool to detect and quantify subclinical and clinically apparent lesions in patients with defined cervical spinal stenosis.

Electric non-invasive stimulation of the motor cortex was performed in 19 healthy subjects. Muscle responses were recorded with surface electrodes from the abductor, pollicis brevis and anterior tibial muscle. The mean central motor latencies for pathways regulating the function of the upper limbs was 4.5 msec (standard deviation 0.5 msec), the corresponding latency for the lower limbs was 9.6 msec (standard deviation 1.2 msec). The reproducibility of latencies and configuration of the potentials obtained indicates that the method described can be used as a reliable method in the diagnosis of affections of the motor system.

The decline in the high incidence of amyotrophic lateral sclerosis, parkinsonism, and Alzheimer-type dementia among the Chamorro population of the western Pacific islands of Guam and Rota, coupled with the absence of demonstrable viral and hereditable factors in this disease, suggests the gradual disappearance of an environmental factor selectively associated with this culture. One candidate is seed of the neurotoxic plant Cycas circinalis L., a traditional source of food and medicine which has been used less with the Americanization of the Chamorro people after World War II. Macaques were fed the Cycas amino acid beta-N-methylamino-L-alanine, a low-potency convulsant that has excitotoxic activity in mouse brain, which is attenuated by N-methyl-D-aspartate receptor antagonists. These animals developed corticomoto-neuronal dysfunction, parkinsonian features, and behavioral anomalies, with chromatolytic and degenerative changes of motor neurons in cerebral cortex and spinal cord. In concert with existing epidemiological and animal data, these findings support the hypothesis that cycad exposure plays an important role in the etiology of the Guam disease.

N-Isopropyl-p-123I-amphetamine (123I-IMP) single photon emission computer tomography studies were performed on 17 patients suffering from amyotrophic lateral sclerosis (ALS). All patients displayed varying degrees of impaired fixation of 123I-IMP in the whole brain. These findings were not related to the clinical variants of ALS and the age of the patients. A correlation between the severity of the disease and the degree of impaired fixation could be observed. In addition, patients suffering from ALS for longer periods showed more pronounced impairment of 123I-IMP fixation.

Non-invasive direct stimulation of the motor cortex of cynomolgus monkeys has been used to assess in awake and anesthetized animals the central and peripheral conduction times of the motor pathway and to measure the latencies of the descending spinal volley of the pyramidal tracts. Repetitive stimulation failed to induce convulsive activity or detectable pathological changes. Peripheral latencies were comparable with those obtained from F-wave analysis. Central conduction times for corticospinal tracts regulating the upper and lower limbs were 2.7 msec and 5.4 msec, respectively, the estimated conduction velocity (67.5 m/sec) corresponding to results obtained by invasive methods. These studies provide a new and apparently safe technique to assess non-invasively the functional status of the central motor pathway in primates, a method that might also find utility in clinical practice.