Abstract #1412763: Hustle for The Muscle: A Rare Case of Non-traumatic Rhabdomyolysis Secondary to Thyrotoxicosis

Abstract

Rhabdomyolysis (RM) is a rare potentially life-threatening condition characterized by breakdown of striated muscle which can lead to progressive acute kidney injury. Common etiologies include trauma, infection, drugs, or surgery. Rarely, endocrinopathies including thyrotoxicosis have been associated with RM. Here, we present a case of non-traumatic and non-exertional RM secondary to thyrotoxicosis. A 50-year-old man recently diagnosed with Graves’ disease a month ago presented to the hospital with fever for 3 days. A week prior to presentation, thyroid function tests (TFT) showed normalizing FT4 (1.13ng/dL) and T3 (112ng/dL) levels with low TSH (<0.005ulU/m) which prompted his endocrinologist to decrease the methimazole dose from 20mg thrice daily to 10mg once daily. His fever was associated with nausea, vomiting, chills, and non-bloody diarrhea. On admission, the following vital signs were obtained: temperature 101.6F, blood pressure 140/85 mmHg, pulse rate 108 bpm, respiratory rate 16 bpm, and oxygen saturation 99% on room air. He was found to be alert, conscious, and coherent. Physical examination was notable for exophthalmos, absence of jugular vein distention, diffusely enlarged non-tender thyroid, clear breath sounds, no jaundice, and no peripheral edema. His calculated Burch-Wartofsky score was 40. Laboratory evaluation showed leukocytosis, elevated FT4 (4.01ng/dL), elevated FT3 (5.87pg/mL), and low TSH (<0.015uIU/mL) levels. He was also found to have acute kidney injury with creatinine of 1.33 mg/dL associated with hemoglobinuria. Further testing revealed a significantly elevated creatinine kinase (CK) at 98,760 U/L. On imaging, chest x-ray and CT scan were consistent with left lower lobe pneumonia. During the hospital stay, the patient was treated with methimazole 20mg daily together with antibiotics, aggressive hydration, and propranolol. His kidney function initially rapidly worsened but eventually improved as the CK levels normalized. FT4 levels were monitored and it gradually trended back to normal after 5 days. He was discharged stable and advised to follow up with his endocrinologist after a week. This is a case of a thyrotoxicosis complicated by rapidly worsening renal function. With a markedly elevated CK level accompanied by hemoglobinuria, absence of trauma or physical exertion, patient developed a concomitant non-traumatic RM. Non-traumatic RM is a rare complication of thyrotoxicosis and/or hyperthyroidism. Due to increased metabolic rate and energy consumption, rapid depletion of myocyte energy storage and substrates escalates, ultimately leading to necrosis. Based on literatures, only four cases were reported regarding the similar condition. In these cases, CK levels reported was less than 10 times the normal range. Our patient is unique that without history of trauma or exertion, a non-traumatic, non-drug-induced rhabdomyolysis transpired in the setting of acute thyrotoxicosis, with CK levels almost 580 times the upper normal limit. Management wise, aggressive hydration remains the treatment of choice to provide adequate renal perfusion and prevent renal damage.