The Effects of Testosterone and Transcutaneous Muscle Stimulation on Strength and Muscle Mass in Myotonic Dystrophy

Abstract

         In myotonic dystrophy type 1 (DM1) quadriceps weakness often results in severe functional limitations and genu recurvatum. To improve quadriceps strength the effects of isometric tetanic contractions using transcutaneous muscle stimulation (TMS) and testosterone enanthate (TE) were assessed. Ten DM1 subjects underwent unilateral TMS 6 hours per day for 14 days. The stimulated leg was randomly assigned and sham stimulation was done on the opposite leg by transcutaneous nerve stimulation. Muscle mass was estimated by cross-sectional area computed tomography and strength was measured by Cybex ergometry. Following the initial TMS period, 8 of 10 subjects were given a 12-week course of TE (3 mg/kg/wk) followed by 14 days of TMS. Neither TMS nor TE improved strength.  Following 12 weeks of TE, there was an average increase in muscle mass of at least 8.7 +/- 1.6 cm2. These findings are consistent with the TE—increased muscle mass in DM1 as measured by creatinine clearance and total body potassium. The dissociation of mass and strength following TE and the failure of exercise to improve strength may have significance in characterizing the muscle defect in DM1.