A 43-Day-Old Male With Respiratory Distress and Acute-Onset Hypotonia

A 43-day-old, full-term, previously healthy male presented with decreased activity and oral intake. He was found to be grunting and hypoxemic on examination, and a respiratory pathogen panel was positive for rhinovirus. He was diagnosed with presumed bronchiolitis. His neurologic exam on admission was normal. Because of respiratory failure, he was escalated from high-flow nasal cannula to bilevel positive airway pressure upon admission and he was started on ceftriaxone and vancomycin while awaiting culture data. On hospital day 6, he required escalation of respiratory support. His examination at that time was notable for new hypotonia of his bilateral upper and lower extremities, sluggish pupils, bilateral exotropia, intermittent vertical nystagmus, and an absent Moro reflex. He developed a focal seizure and a computed tomography of the brain demonstrated simple right otomastoiditis. The seizure was attributed to a serum sodium of 113 mmol/L in the setting of syndrome of inappropriate antidiuretic hormone secretion, thought to be secondary to viral bronchiolitis. However, as the patient's sodium was corrected to a normal range, he continued to have neurologic deficits on examination. Given his persistent hypotonia and respiratory failure, atypical for the expected course of viral bronchiolitis, the patient underwent an extensive neurologic and infectious workup, which ultimately revealed a surprising diagnosis.