The corticomotor threshold is not dependent on disease duration in amyotrophic lateral sclerosis (ALS)

INTRODUCTION: It is suggested that early in ALS the corticomotor threshold (CMT) is low, but increases with increasing duration of the disease. POPULATION AND METHODS: We compared CMT, central conduction time and motor-evoked response/M-wave amplitude in two populations of ALS patients: one with disease duration shorter than 6 months (Group A, 11 patients) and another who had had the disease for more than 24 months (Group B, 14 patients). These two groups were compared with a control group of 30 subjects. In all the ALS patients, abductor digiti minimi (ADM) strength was greater than MRC 3. RESULTS: M-wave amplitude was comparable in the three groups. We found no difference between the three groups in these transcranial magnetic stimulation studies and there was no correlation between disease duration time and CMT. CONCLUSION: We did not confirm a relation between CMT and disease duration. An increased CMT late in the disease progression is associated with greater lower motor neuron loss, and greater corticospinal tract degeneration with dispersion of the descending motor volley.