Exacerbation of acetazolamide-responsive sodium channel myotonia by uterotonic agents

The symptoms of myotonia can worsen during pregnancy and tocolysis with ritodrine has been associated with rhabdomyolysis. We describe a patient with myotonia who developed hypertonus immediately following the administration of uterotonic agents. A 24-year-old, G2P1 at 31 weeks of gestation with a history of acetazolamide-responsive myotonia presented with premature rupture of membranes. During cesarean delivery she experienced significant hypertonus of the upper limbs, shoulders, fingers, and mouth immediately after intravenous administration of oxytocin 5 IU and methylergometrine maleate 0.2 mg. The mechanism underlying increased muscle tone in response to these drugs remains unclear. Anesthesiologists should be especially attentive to the administration of uterotonic drugs during the management of pregnant myotonia patients.