Unmasking Hypothyroidism: A Reversible Cause of Hypercapnic Respiratory Failure in a Patient with Complex Pulmonary Comorbidities

Introduction: Severe hypothyroidism may manifest as hypercapnia and drowsiness, symptoms that can easily be overlooked in patients with comorbidities such as COPD, pneumonia, or a history of lung resection. Recognizing the clinical signs of hypothyroidism and initiating timely treatment is crucial to preventing myxedema coma. Case: A 67-year-old male patient presented with acute-on-chronic hypoxic respiratory failure secondary to pneumonia, with a background of COPD and lung cancer status post-lobectomy and chemotherapy. Despite receiving respiratory management, the patient remained drowsy and continued to retain carbon dioxide. Further evaluation revealed severe hypothyroidism, for which levothyroxine therapy was initiated. Following treatment, the patient's drowsiness and oxygen requirements improved significantly. Conclusion: This case highlights the importance of considering severe hypothyroidism as a reversible cause of hypercapnic respiratory failure and altered mental status, especially in patients with complex pulmonary comorbidities. Early recognition and prompt thyroid hormone replacement can prevent myxedema coma, underscoring the need for thorough evaluation beyond common respiratory causes in such cases.