The Myasthenic Reactions

Abstract

The most familiar of all electrophysiological findings in Myasthenia Gravis is the fall in amplitude of successive motor responses during repetitive stimulation (Fig. 1). This decrementai response may repair initially, but the progress is towards extinction as stimulation is continued at high frequencies. Following a tetanus, a short period of facilitation is observed and this is followed by a longer period of exhaustion, during which the neuromuscular transmission defect is enhanced. The significance of these reactions may be interpreted differently and even now, the site of the primary anatomical defect is not fully established. Recent physiological (Dahlback et al., 1961; Hofmann and Stemmer, 1963) and pathological (Fenichel and Shy, 1963; Brody and King Engel, 1964) findings stress the importance of presynaptic abnormalities, and I propose to submit further evidence that the basic defect involves the motor nerve terminals.