Abstract #1408127: A Case of Rhabdomyolysis Resulting in Fulminant Acute Kidney Injury in a Patient with Severe Hypothyroidism

Abstract

Rhabdomyolysis is characterized by muscle necrosis and the release of intracellular muscle contents into circulation. Hypothyroidism is known to be associated with musculoskeletal problems, rarely rhabdomyolysis. We report a case of severe hypothyroidism due to a prior thyroidectomy with poor medication adherence, who presented with rhabdomyolysis resulting in severe acute kidney injury requiring urgent dialysis. A 65-year-old male with a past medical history of papillary thyroid cancer status post total thyroidectomy presented with lethargy, confusion, decreased oral intake and decreased urination. He recently ran out of levothyroxine. Notably, the patient had also been taking rosuvastatin. On examination, the patient was afebrile, with a pulse of 70 bpm and blood pressure of 111/70 mmHg. He was oriented to self and place but not to time. He demonstrated slow deep voice along with macroglossia and trace non-pitting lower extremity edema. There were no signs of proximal myopathy or neurological deficits. Workup was remarkable for TSH >90.00 mcU/mL, free T4 < 0.1 ng/dl, CPK 22,030 mcg/L, AST 233 U/L, ALT 205 U/L, creatinine 31.6 mg/dl, and BUN 124 mg/dl. The last known TSH was 4.5, free T4 was 1 ng/dL, and creatinine was 0.9 in January 2021. The urine specimen was positive for loaded red blood cells. Renal ultrasound showed no obstruction. Diagnosis of rhabdomyolysis with acute renal failure was made and he was promptly started on dialysis. Endocrinology was consulted and he was started on intravenous levothyroxine. A renal biopsy confirmed acute tubular necrosis due to rhabdomyolysis. After several days, his symptoms improved, and he was transitioned to oral levothyroxine however he remained on dialysis on discharge. Hypothyroid myopathy is most often limited to myalgia, cramps, and sometimes mildly elevated levels of muscle enzymes. Rhabdomyolysis can rarely develop due to severe hypothyroidism. Muscle breakdown in hypothyroidism is caused by poor contractility, low myosin ATPase activity, and low ATP turnover in the skeletal muscles. These metabolic abnormalities may sensitize patients with hypothyroidism to develop rhabdomyolysis. Acute renal failure, as a result of an accumulation of myoglobin in renal tubules, is the most life-threatening complication of rhabdomyolysis and can develop in up to 33% of patients. There have been very few case reports of hypothyroidism causing rhabdomyolysis, with a precipitating factor such as exercise, trauma, or drugs such as statin. Our patient presented with severe hypothyroidism complicated by rhabdomyolysis resulting in acute renal failure requiring dialysis. The patient was also on a statin which may cause statin-induced rhabdomyolysis due to hypothyroidism. This case emphasizes the importance of adherence to levothyroxine in hypothyroid patients as well as the importance of considering rhabdomyolysis in patients with severe hypothyroidism as a cause of acute renal failure. It also shows the importance of reviewing the patient's medication list and discontinuing all those medications which can escalate the process of rhabdomyolysis in a patient with hypothyroidism.