Out-of-Hospital Cardiac Arrest As the Initial Presentation of Myxedema Coma.

Myxedema coma is a rare, life-threatening manifestation of severe hypothyroidism that typically presents in hospitalized patients with hypothermia, bradycardia, and altered mental status. In exceptionally rare instances, it may present with cardiac arrest as the initial manifestation. We report a case involving a woman in her late 50s with obesity, obstructive sleep apnea, and previously undiagnosed hypothyroidism who experienced a witnessed out-of-hospital cardiac arrest. Following successful resuscitation, she was found to have profound hypothermia and bradycardia. Laboratory investigations revealed markedly decreased thyroid hormone levels with only modest elevation in thyroid-stimulating hormone. Her family reported a history of progressive lethargy, weight gain, cold intolerance, and confusion over several months. A prior elevated TSH had been documented one year earlier. Thyroid peroxidase antibodies were positive, while TSH receptor antibodies were negative. She was treated with high-dose intravenous levothyroxine and liothyronine, in addition to intensive supportive care. Although her thyroid function improved biochemically and transient clinical improvement was noted, she developed aspiration pneumonia and progressed to septic shock, resulting in death on the fifth day of admission. This case highlights the diagnostic challenge posed by myxedema coma, especially when TSH elevation is modest. Clinicians should maintain a high index of suspicion for endocrine causes of cardiac arrest and initiate prompt hormone replacement when indicated.