Sudomotor dysfunction in amyotrophic lateral sclerosis.

We performed a quantitative sudomotor function test on 11 patients with classic amyotrophic lateral sclerosis (ALS) and 11 age-matched control subjects. Thermal warming increased the sweat rate in the forearm of ALS patients and in the forearm and thigh of control subjects. The sweat rate in the thigh of ALS patients was lower than that of controls. Thyrotropin releasing hormone increased the sweat rate in the forearm and thigh and decreased oral temperature in both ALS and controls but the lower extremity response was reduced in ALS. Results of the sudomotor axon reflex test on the thigh indicate that in ALS, there is mild postganglionic sudomotor dysfunction. We conclude that patients with ALS have mild thermoregulatory sweat dysfunction due to postganglionic lesions in the lower extremities.