Pearls & Oy-sters: Severe Myotonic Crisis Resembling Malignant Hyperthermia

Patients with myotonic disorders are at risk for severe generalized muscle contraction, referred to as a "myotonic crisis." For those patients with nondystrophic myotonia (NDM), the most common trigger of a myotonic crisis is exposure to succinylcholine. In this case, a 10-year-old female patient with NDM secondary to an SCN4A pathogenic variant developed a severe myotonic crisis in the setting of an upper respiratory infection and asthma flare treated with a beta-adrenergic agonist (ß-agonist). She presented with generalized rigidity and features of hypermetabolism resembling an anesthetic-related malignant hyperthermia. Management necessitated multidisciplinary collaboration, a complex intubation strategy, and an extended course in the pediatric intensive care unit. We suspected that this crisis was precipitated in part by continuous ß-agonist use during her initial asthma management. Treatments targeting sequential steps of the myocyte activation cascade tempered the contractile apparatus leading to clinical improvement in rigidity.