ICU Management of Severe Myotonic Crisis in the Setting of Beta-Adrenergic Agonist Use: A Case Report
Ashna Aggarwal1, Anil Wadhwani1, Steven Loscalzo2, Megan McSherry2, Justin Lockman2, John Brandsema3, Jennifer McGuire3, Susan Matesanz3
1Department of Neurology, University of Pennsylvania Perelman School of Medicine, 2Department of Anesthesiology and Critical Care Medicine, 3Division of Neurology, Children’s Hospital of Philadelphia
Background:
Nondystrophic myotonias (NDM) include skeletal muscle sodium and chloride channelopathies, which result in muscle hyperexcitability due to a postsynaptic channel mutation. Rarely, myotonic disorders are complicated by “myotonic crisis,” a severe, generalized, sustained muscle contraction classically caused by succinylcholine. These crises are distinct from malignant hyperthermia (MH) because they lack features of hypermetabolism including hyperthermia and acidosis. We describe critical care management of a pediatric patient with SCN4A-associated NDM who developed a severe MH-like crisis in the setting of recent illness and beta-adrenergic agonist use.
Results:
A 10-year-old female with SCN4A-associated NDM and asthma presented to the ED with status asthmaticus and was treated with continuous albuterol and intravenous steroids. She developed worsening myotonia, rhabdomyolysis, and acidosis. Despite mexiletine and lorazepam, she developed progressive respiratory failure necessitating intubation. Due to severe masseter spasm, she was intubated via a trans-laryngeal mask airway fiberoptic approach. Her ICU course included worsening respiratory failure, persistent severe muscle rigidity with associated rhabdomyolysis, and hyperthermia. Multi-modal pharmacologic therapy targeted both presynaptic and postsynaptic signaling in the myocyte contractile apparatus, allowing for muscle relaxation. She was extubated after 13 days and discharged after 28 days with rehabilitation to near-baseline function. Genetic testing did not reveal additional risk factors for MH susceptibility. Six and ten months post-discharge, she had two short admissions for asthma exacerbations managed without beta-adrenergic agonists, and was discharged both times without myotonic crisis.
Conclusions:
Existing literature suggests myotonic crises are physiologically distinct from MH. However, severe generalized muscle contraction, in this case precipitated by an SCN4A gain-of-function mutation and exacerbated by beta-adrenergic agonist use, can lead to features of hypermetabolism including hyperthermia and acidosis. This case promotes careful consideration when prescribing beta-adrenergic agonists to patients with known or suspected myotonia, and provides guidance for early critical care management of patients presenting with severe crises.
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