SAT-318 - When Breathlessness Was More than COPD: Thyrotoxicosis Causing Acute Hypercapnic Respiratory Failure

Introduction: Thyroid storm (TS) is a rare, life-threatening manifestation of hyperthyroidism characterized by multiorgan dysfunction and cardiovascular instability, with reported mortality of 3.6–17%. Respiratory failure is an uncommon, severe complication presenting with hypoxemia and hypercapnia, requiring urgent intervention. We describe a case of thyroid storm presenting with acute hypercapnic respiratory failure and hemodynamic instability.

Case Report: A 58-year-old woman with COPD on 4 L home oxygen, hyperthyroidism on methimazole, atrial fibrillation on anticoagulant presented with two days of dyspnea and chest heaviness. She was tachycardic to the 170s in atrial fibrillation with rapid ventricular response, with oxygen saturation 98% on baseline oxygen. Examination revealed diffuse wheezing without thyroid eye findings. Laboratory testing showed suppressed thyroid stimulating hormone (TSH) (0.002 µIU/mL) and elevated free thyroxine (T4) (2.5 ng/dL). She was initially treated for presumed COPD exacerbation. Persistent tachycardia with biochemical evidence of thyrotoxicosis raised concern for thyroid storm, prompting initiation of hydrocortisone, propranolol, and propylthiouracil. She subsequently developed lethargy, hypotension, and severe hypercapnia (PCO₂ 144 mmHg), requiring emergent intubation, ICU transfer, and vasopressor support. With supportive care and antithyroid therapy, she was extubated and stabilized. Free T4 decreased to 1.6 ng/dL by day five. She was transitioned to methimazole, continued propranolol, and tapered off steroids.

Discussion: Thyroid storm occurs in up to 0.2% of patients with hyperthyroidism and is most commonly due to Graves’ disease. Precipitatingfactors include medication nonadherence, acute physiological stressors including infection, surgery. Respiratory failure in thyroid storm is multifactorial, driven by increased metabolic demand with excess carbon dioxide production, cardiac dysfunction, neurologic impairment, and reduced ventilatory reserve, particularly in patients with underlying lung disease. Management requires prompt multimodal therapy with thionamides, beta-blockade, glucocorticoids, and intensive care.

Conclusion: Thyroid storm should be considered in patients with hyperthyroidism who develop acute hypercapnic respiratory failure, especially when clinical deterioration is disproportionate to baseline pulmonary disease. Early recognition and treatment are critical to prevent rapid clinical decline and improve outcomes.

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