Continuous muscle fiber activity in the Schwartz-Jampel syndrome

Abstract

The Schwartz-Jampel syndrome is an hereditary disease characterized by shortness of stature, muscular hypertrophy, and persistent muscular contraction at rest. The electromyographic (EMG) findings have been referred to by all authors as myotonia. In the two cases described in this article, the EMG findings were quite different from ordinary myotonia. There was continuous electrical activity at rest which did not wax and wane and accounted for the persistent muscular contraction observed clinically. This activity was not abolished by deep general anesthesia. The technique of regional neuromuscular block with curare was used to determine the origin of these discharges. In contrast to classical myotonia, the discharges were abolished by curare, and muscular relaxation was achieved. However, the likelihood that they do originate from the muscle component of the neuromuscular junction rather than the peripheral nerve was suggested by the observation that spontaneous electrical activity persisted long after inadvertent nerve injury during a surgical procedure. We suggest that the term myotonia is not appropriate for the high frequency discharges observed in this syndrome. Regional intravenous perfusion with curare is a relatively simple technique which can assist in localizing the site of origin of abnormal EMG discharges. The application of this anesthetic technique to physiological studies of the motor unit is described.