Transcranial magnetic stimulation compared with upper motor neuron signs in patients with amyotrophic lateral sclerosis.

If patients with amyotrophic lateral sclerosis (ALS) present without upper motor neuron signs (UMNS) they do not meet current ALS research criteria. To compare how sensitively degeneration of upper motor neurons is detected clinically and by transcranial magnetic stimulation, 35 patients with ALS were studied. Nineteen patients had definite UMNS, nine patients had probable UMNS, and seven patients had no UMNS. Cortex, cervical nerve roots, and lumbar plexus were stimulated with a magnetic stimulator. Compound muscle action potentials from abductor digiti minimi and from anterior tibial muscles were recorded with surface electrodes. Responses to transcranial magnetic stimulation were considered abnormal if central motor conduction time was above the 99% upper limits or if there was no response to cortical but to peripheral stimulation. In all patients with definite UMNS central motor conduction was abnormal. In patients with probable UMNS it was abnormal in 67%, and in patients without UMNS it was abnormal in 71%. Abnormality of central motor conduction was neither correlated with the duration nor with the severity of the disease. The high rate of abnormalities of central motor conduction found in patients with ALS but without definite UMNS suggests that, in these patients, the diagnosis of ALS can be made more reliably if transcranial magnetic stimulation studies are performed.