DURING THE COURSE of their illness, patients with amyotrophic lateral sclerosis may have complaints of, and may demonstrate on clinical and laboratory examination, unusual puscle fatigability resembling that of myasthenia gravis. Other features of amyotrophic lateral sclerosis usually are sufficient to differentiate it from myasthenia gravis. However, it is im-portant to recognize this occurrence of a myasthenic syndrome in amyotrophic lateral sclerosis to avoid confusion and uncertainty in diagnosis.

The presence of a significant defect of neuromuscular conduction in patients with diseases affecting the lower motor neurons has been suggested by others. Hamill and Walker1 reported improvement of muscular strength after injection of neostigmine (Prostigmin) in patients with a variety of diseases of the motor system. In poliomyelitis, Buchthal and Honckez observed unusual fatigability of motor units manifested in electromyographic studies by a gradual decrease in amplitude of their action potentials as seen during a sustained contraction. This was observed frequently in poliomyelitis by Pinelli and Buchthal, 3 but it was found only exceptionally in other diseases of