MYOTONIA ASA SIDEEFFECTOF DIURETICACTION

1 Commonlyusedloopdiuretics produce sideeffects inman which are similar tochemically induced myotonia. Thesediuretics havestructural affinity withknownmyotonic agents. 2 Wehaveobserved EMG myotonia invivoinlegmuscles ofratstreated withintravenous frusemide. 3 Inthe presenceofseveral different diuretics, ratisolated diaphragm, soleus andextensor digitorum longus muscles aswell asfrogsartorius muscles produce typically myotonic contractions withrelaxation times up toseveral seconds. 4 Intracellular recording ofaction potentials fromdiuretic-treated muscles reveals longlasting after-discharges following a brief electrical stimulus, again typical ofchemically induced myotonia. 5 Having demonstrated amyotonic action ofseveral diuretics we suggest aneedforcaution inusing these drugs inpersonswithhereditary myotonia anda needtobeaware ofpossible provocation of myotonia insubclinical cases.Myopathies andneuropathies which areknowntoresult fromchronic exposuretomyotonic agentsalso needtobeconsidered. 6 Inourstudy, thediuretic, acetazolamide, unmasked subthreshold myotonia. Thisseemstobeat variance withreports ofitsusefulness inthetreatment ofmyotonia. 7 Diuretics should probably notbeemployed inthetreatment ofherbicide intoxication wheretheir myotonic activity wouldbeexpected toaddtotheknownmyotonic activity oftheherbicide.