Clinical, neurophysiological and morphological findings in Eaton Lambert syndrome

Two patients with maysthenic syndrome apparently not associated with carcinoma were studied in detail with repetitive stimulation of motor nerves, single fibre electromyography and histology. One patient showed signs of widespread autonomic dysfunction and the other patient had multifocal CNS symptoms of unclear etiology. Both cases showed a marked improvement with guanidine treatment which could be documented by the electrophysiological investigations. Due to severe adverse effects of the guanidine treatment on kidney, pancreatic and bone marrow functions the drug had to be withdrawn. Edrophonium given intravenously caused a marked and longlasting improvement of the muscle weakness and of the neurophysiological parameters. The mechanism of action is suggested to be different from that seen in myasthenia gravis. Single fibre electromyography showed a marked increase of neuromuscular jitter and blockings which decreased with increasing innervation frequency. The morphological study showed a selective affection of type II (fast twitch) fibres, a finding which is suggested to be secondary to an impaired neuromuscular transmission in the type II motor units.