(284) Low T3 Syndrome: An Unusual Case of Myxedema Coma in a Critically Ill Patient

Introduction: Low triiodothyronine (T3) syndrome is defined by low serum T3 with normal thyroxine (T4) and thyroid-stimulating hormone (TSH) levels. Often found in critically ill patients, it is thought that the peripheral conversion of T3 to T4 is inhibited as a reflection of a decreased metabolism during the stress state. Herein we present a case of low T3 syndrome and myxedema coma in the setting of acute respiratory failure.

Description: An 80 year-old male with atrial fibrillation and diabetes presents with three days of cough, nausea, vomiting, and generalized weakness. Imaging demonstrated right lower lobe and retrocardiac infiltrates for which antibiotics and supplemental oxygen via nasal cannula were administered to treat for community-acquired pneumonia. He deteriorated clinically, eventually developed atrial flutter with rapid ventricular response and progressive hypoxemic respiratory failure leading to intubation and mechanical ventilation. Initial labs showed leukocytosis with neutrophil predominance, mild hyponatremia, hypokalemia and hypomagnesemia. Baseline TSH was normal. There was initial concern for acute respiratory distress syndrome for which dexamethasone was initiated. However, the patient had rapid improvement of respiratory status and required minimal support from mechanical ventilation. Despite weaning of analgesic and sedation medications, he remained persistently encephalopathic on day 10 of hospitalization. Workup was negative for acute intracerebral pathology. Repeat TSH was low at 0.4 mIntUnit/L, free T4 normal at 0.8 ng/dL, but T3 total undetectable at < 25 mg/dL, indicating low T3 syndrome. Given concurrent generalized edema and hypothermia, myxedema coma was suspected and liothyronine 10 mcg daily was started. Marked improvement of encephalopathy was noted within two days. He was awake, responsive, and was appropriate for liberation from mechanical ventilation.

Discussion: Low T3 syndrome is usually self-limiting as the underlying illness improves. Myxedema coma, on the other hand, is an endocrine emergency requiring immediate recognition and treatment with thyroid supplementation. Our case demonstrates the need for further research in thyroid dysfunction among the critically ill, including relevance of screening, threshold for treatment, and long-term outcomes.