[Congenital myotonia. Report of 7 patients]

Myotonia is the phenomenon of decrease of muscular relaxation rate, after either a contraction or a mechanical or electrical stimulus. Congenital myotonias are hereditary affections and do not present muscular dystrophy. The current trend is to group them as ionic channels diseases, together with the periodic paralysis. The authors accompanied the cases of seven patients, six males and one female, with ages ranging from 16 to 48 years (average 27 years) and onset of symptoms between 1 and 10 years (average 5 years). These patients presented a myotonic phenomenon unleashed by intensive contraction and global muscular hypertrophy. Three patients were diagnosed as cases of Becker type generalized myotonia because they presented a recessive autosomic heredity and/or transient episodes of muscular weakness. Two patients fitted the description of Thomsen congenital myotonia, with a pattern of dominating autosomic heredity and/or absence of weakness episodes or worsening factors for their condition. Two patients presented fluctuating myotonia, which because worse in cold weather or at potassium intake. The clinical diagnosis was confirmed through complementary tests (electroneuromyography, muscle biopsy and DNA study). Each of the patients made use of different drugs, in the search of optimal lessening of their myotonia. There were five reports of amelioration with the use of diphenilhydantoine; one report with the use of carbamazepine; three reports with the use of acetazolamide; one report with the use of a calcium channel blocker; one report with the use of a beta-adrenergic; one report with the use of thiazide; and none with the use of quinidine/procainamide.