Antimyotonic therapy with tocainide under ECG control in the myotonic dystrophy of curschmann-steinert

Abstract

Ten patients suffering from advanced myotonic dystrophy with severe myotonic symptoms were treated with 800-1200 mg/day of the anti-arrhythmic drug tocainide (Xylotocan). All patients reported a marked subjective improvement of myotonia, which was confirmed by objective tests. Except for a slight QT-prolongation in one patient, the ECG was not significantly altered by the treatment. Twenty-four-hour ECG after treatment disclosed that pre-existing ventricular arrhythmia disappeared in three cases. The occurrence of complex ventricular arrhythmia in two patients under treatment was not necessarily due to specific effects of the drug but might be explained by the high spontaneous variability of rhythm disorders. In these patients suffering from myotonic dystrophy with typical cardiomyopathy no deleterious effects of the drug were observed, especially no cardiac arrhythmias which would have necessitated interruption of treatment. Therefore, the authors recommend symptomatic therapy with tocainide for myotonia and paramyotonia congenita, as well as in myotonic dystrophy patients suffering from marked myotonic stiffness. ECG and 24-h ECG should be carefully recorded as necessary in any treatment with anti-arrhythmic drugs.

Mexiletine is an effective antimyotonia treatment in myotonic dystrophy type 1

“…2) These trials were double-blind; previous trials of mexiletine or tocainide for myotonia in DM1 have been single blind 7 or unblinded. 8 3) The improvement in myotonia noted in our first trial was corroborated by the second. 4) Plasma concentrations of mexiletine were measured, a requirement for the tocainide study, 8 but not in the previous mexiletine study.…”

“…8 3) The improvement in myotonia noted in our first trial was corroborated by the second. 4) Plasma concentrations of mexiletine were measured, a requirement for the tocainide study, 8 but not in the previous mexiletine study. 7 5) These trials employed a carefully tested method of measuring grip myotonia 28,29 that has good test-retest reproducibility, and yields grip relaxation times that increase and grip peak forces that decrease as CTG repeat lengths increase.…”

“…31 Still, treatment with these drugs in cardiac patients typically has little effect on PR, QRS, and QT duration, or on hemodynamic function. 31 Similarly, previous studies of mexiletine and tocainide 7,8 in patients with myotonic myopathy of various types have also shown no significant changes in EKG measurements. Our study supports the view that mexiletine at dosages of 150 to 200 mg TID has no significant effect on cardiac conduction over a 7-week treatment period in patients with DM1 who have no significant cardiac risk factors except for first-degree AV Block.…”

“…7 Overall, our data suggest that mexiletine at oral dosages of 150 -200 mg TID may be considered as an effective, symptomatic treatment in patients with DM1 with functionally significant myotonia, and appears to be safe in the short term. Moreover, because the study required the presence of clinical myotonia, but did not specifically require moderate or severe myotonia as in 2 prior trials, 7,8 we believe that our data are generalizable to typical patients with DM1 with clinically evident myotonia. The percentage improvement in grip RT was not significantly greater in the 200 mg TID trial than in the 150 mg TID trial.…”

“…7 (Although tocainide has also been reported to be effective in treating myotonia, 8 bone marrow suppression 8,25 limits its use.) While this study 7 was an important step forward, it had some deficiencies: short duration (4 weeks), a heterogeneous patient group, a single-blind study design, heterogeneous treatment group sample sizes, and incomplete validation of the methods used to measure myotonia.…”