(21.16) A Deadly Outcome of Subclinical Hypothyroidism, A Case of Post-Operative Myxedema Coma.

Even though myxedema coma incidence has decreased, it is still considered a rare diagnosis with a high mortality rate. Major surgeries are unrecognized risk factors, with only fourteen post-operative myxedema coma cases described in the English literature. Clinical identification is crucial since prompt diagnosis and treatment are paramount for survival. We present a case of myxedema coma after femur intramedullary rod fixation.

Case(s) Description :

An 86-year-old male with a history of heart failure with reduced ejection fraction, atrial fibrillation on anticoagulation, and subclinical hypothyroidism was seen on day 5 of post-operative, with the inability to wean off vasopressors and lethargy. He was hypothermic (35.8oC), on pressor support (MAP: 67), and bradypnea (respiratory rate: 10 per minute). On examination, he was lethargic with non-pitting edema of all extremities. Three months pre-operative laboratories showed TSH 6.6 uIU/mL (0.27-4.20 uIU/mL) and free T4 1.1 ng/dL (0.9-1.8 ng/dL). Post-operatively, TSH uptrended (23.6 uIU/mL) with low free T4 (0.3 pg/mL). Additional laboratories showed respiratory acidosis (pH: 7.31, PCO2:62 mmHg), normoglycemia, and no electrolyte abnormalities. Adrenal insufficiency was ruled out. The patient’s presentation, combined with the diagnostic scoring system for myxedema coma, led to a total of 65 points, highly suggestive of the disease. He received a 200 mcg IV loading dose of levothyroxine, followed by 50 mcg/day and hydrocortisone 50 mg/every 6 hours. Subsequently, he was awake and weaned off vasopressor. Unfortunately, he expired due to acute hypoxemic respiratory failure.

Discussion :

In major surgeries, there is high metabolic demand with a subsequent decrease in peripheral conversion of T4 to T3 and TSH secretion, which prompts hypothyroid complications, including myxedema coma. Since it is not usually considered a typical diagnosis in the post-operative or intensive care setting, it is paramount to pre-operatively stratify patients into three hypothyroid categories (well-controlled, mild-moderate, and severe) to address the need for medical optimization. Myxedema coma usually manifests in long-standing hypothyroid patients. However, this case demonstrates that even in a subclinical hypothyroidism, the combination of major surgery in a highly comorbid patient can result in a lethal myxedema coma. Even though hypotension and altered mental status can be attributed to anesthetics or drug effects in the post-operatory period, it is important to consider myxedema coma as part of the differentials, independently of previous thyroid function status. Failure to recognize the severity can be fatal, and immediate treatment is lifesaving.