SUN-372 Myxedema Coma with Preserved T4 Levels, A Diagnostic Challenge

Abstract Disclosure: K. Zaleski: None. S. Prasad: None. A. Jala: None. M. Singh: None. S. Ball: None. D. Thor: None. R. Patel: None. G. Das: None. H. Ehsan: None. Background: Myxedema coma is a rare, life-threatening manifestation of hypothyroidism, typically characterized by low serum T4 and elevated TSH levels. However, its presentation with relatively preserved T4 levels is an uncommon occurrence that poses diagnostic challenges. Clinical Case: An 82-year-old female with a history of chronic obstructive pulmonary disease (COPD), pulmonary embolism, and hypothyroidism presented with acute confusion and decreased oral intake for one day. A month prior to admission she was living at home, was hospitalized for pneumonia, and discharged to a rehabilitation facility where she developed insomnia. The patient, previously functionally independent, was reported by her rehabilitation facility to be "confused," "combative," and "refusing all meals." Upon admission, she was found to be hypotensive, bradycardic, and later became hypothermic during hospitalization. She was somnolent and oriented only to person. Initial investigations, including non-contrast CT, 24-hour continuous EEG, and MRI of the brain, revealed no acute abnormalities. Laboratory findings revealed hypoglycemia but were negative for hyponatremia, inflammatory markers, complement abnormalities, and hyperammonemia. An extensive infectious workup, including urinalysis, chest X-ray, blood cultures, and lumbar puncture, was unremarkable. Thyroid function tests demonstrated an elevated TSH of 48.11 mIU/L (n = 0.4-4.5 mIU/L), with a T4 of 0.7 ng/dL (n = 0.6-1.1 ng/dL). T3 was noted to be 35 ng/dL (n = 75-180 ng/dL) and free T3 at 0.6 pg/mL (n = 2-4.4 pg/mL).Given the high clinical suspicion for myxedema coma, the patient was treated with an initial intravenous (IV) levothyroxine loading dose of 200 mcg, followed by a seven-day course of 80 mcg IV daily, with subsequent transition to 50 mcg oral therapy upon discharge. Hydrocortisone therapy was initiated with an IV bolus of 50 mg every six hours for two days, followed by a tapering regimen. The patient demonstrated significant clinical improvement, with TSH levels decreasing to 14.55 mIU/L over four days. Despite the relatively preserved T4 levels, the patient's clinical presentation and response to treatment confirmed the diagnosis of myxedema coma. Conclusion: This case highlights the diagnostic complexity of myxedema coma in the presence of relatively preserved thyroid hormone levels and underscores the importance of TSH as a critical marker for timely diagnosis and intervention in critically ill patients. Presentation: Sunday, July 13, 2025