Severe Adult-Onset Non-Dystrophic Myotonia With Apnea and Laryngospasm Due to Digenic Inheritance of

Objectives: To report a case of adult-onset non-dystrophic myotonia complicated by recurrent episodes of laryngospasm. Methods: The patient is a 35-year-old man who was admitted to our hospital for recurrent episodes of apnea requiring endotracheal intubation with mechanical ventilation. He underwent extensive evaluation, including EMG, laryngoscopy, muscle biopsy, and genetic testing, which revealed a diagnosis of non-dystrophic myotonia. Results: His myotonic disorder was due to the synergistic effects of a pathogenic Discussion: Our case adds to the literature on the potentiating effects of chloride channelopathies on sodium channel myotonia. This is the first reported case of an adult-onset sodium channelopathy manifesting with respiratory failure due to laryngospasm. In addition, we present muscle biopsy findings that have not been described in the recent literature. This case also highlights that a myotonic disorder should be considered in the differential diagnosis for recurrent episodes of mixed hypoxic and hypercarbic respiratory failure.