SAT-622 Rhabdomyolysis: A Rare Initial Presentation of Hypothyroidism

Introduction: Hypothyroidism is associated with a spectrum of musculoskeletal abnormalities as thyroid hormone signaling plays an integral role in skeletal muscle development and contractility. Mild to moderate CK elevation is present in majority of patients with symptomatic hypothyroidism. Overt rhabdomyolysis leading to acute kidney injury as a presentation of undiagnosed hypothyroidism is very rare. We present one such case. Case Description: 47-year-old African American woman with past medical history of non-insulin dependent diabetes and hypertension presented with myalgias and generalized edema in bilateral upper and lower extremities for the past 2 months. Outpatient labs revealed a Creatinine Kinase (CK) level of more than 10,000 U/L and an elevated creatinine level at 2 mg/dL. There was no history of trauma, immobilization, abnormal body movements, new drug use or recent fevers. At presentation, vital signs were stable. Physical examination showed non-pitting edema in bilateral upper and lower extremities. Initial work up revealed a creatinine of 2.15 mg/dL and CK level of 9173 U/L. Serum electrolytes were normal. Urine tested negative for myoglobin. Chest X ray and EKG were normal. Further testing revealed a TSH level of 148.7 mcIU/ml with T3 of <0.40 ng/dl and an undetectable T4 level. A diagnosis of primary hypothyroidism with rhabdomyolysis leading to acute kidney injury was made. She was treated with aggressive fluid resuscitation. She was also started on thyroid hormone supplementation with oral Levothyroxine 200 mcg/day. After initiation of treatment, the Creatinine levels trended down to 1.5 mg/dl. The CK levels trended down to 3600 U/L in 6 days after which she was discharged from the hospital. The patient was followed as an outpatient with gradual reduction of the CK levels over months. CK levels after 1 year were 154 U/L. The patient was continued on supplemental thyroid therapy. Discussion: Rhabdomyolysis is breakdown of muscle cells and release of muscle enzymes like Creatinine Kinase, electrolytes and myoglobin into the circulation. Among the various causes of Rhabdomyolysis, the most common are crush injuries, immobilization, seizures, heat stroke, sepsis and drugs like Statins, Colchicine and toxins like alcohol. Endocrinopathies like Hypothyroidism, Hyperthyroidism, Pheochromocytoma and Diabetes Ketoacidosis have been associated with rhabdomyolysis, but they tend to get ignored due to a lower incidence. Hypothyroidism is associated with elevation in CK levels in about 57-90% patients but the level of CK elevation is only mild, less than 10 times the upper limit of normal. Our case describes an uncommon initial presentation of hypothyroidism leading to overt rhabdomyolysis and acute kidney injury. It emphasizes the importance of checking a thyroid profile in a patient with acute elevation in muscle enzymes without an identifiable trigger.