Effect of dantrolene sodium in myotonic dystrophy

The effect of dantrolene sodium, using a dosage of 120 mg/day, was investigated in 3 patients suffering from myotonic dystrophy. These patients showed a marked reversible deterioration of the clinical symptoms, caused by a reduction of the isometric strength. Dantrolene sodium showed no influence on myotonic discharges and on the latency of the electrical and mechanical muscle response of the adductor pollicis muscle after electrical stimulation of the ulnar nerve. On the other hand a shortening of the relaxation time (in 2 patients) could be observed. The effect of dantrolene sodium on the contractile mechanism without having any influence on the electrical activity is confirmed. Although the relaxation time is shortened, a clinical deterioration is observed, caused by a reduction of the strength. This phenomenon can be explained by a reduction of the calcium release from the sarcoplasmic reticulum after drug application.