A Rare Case of Rhabdomyolysis in a Patient With Pembrolizumab Induced Hypothyroidism

Introduction: Although reported in previous literature, Rhabdomyolysis due to hypothyroidism,without an obvious precipitating factor, is rare. We report a case of severe hypothyroidism leading torhabdomyolysis. Case Report: A 70-year-old man with a history of progressive weakness, myalgia x1 month, statinallergy, pancreatic adenocarcinoma, metastatic melanoma, and acquired hypothyroidism afterreceiving Pembrolizumab for 6 months. He was non-adherent to the levothyroxine, prescribed 1month before hospitalization. He presented to the ED after slipping from his bed onto the floor in aseating position and being unable to get up due to his weakness. Initially, he was afebrile, hypoxic,tachypneic, tachycardic, hypotensive, lethargic, oriented x2, and had a global muscular weakness. Labs were significant for CK of 10,180 (n < 166 IU/L), TSH 136.18(n 0.34-5.6 mU/L), FT4 < 0.25 (n0.6-1.10 ng/dl), FT3 1.4 (n 2.5-3.9 Pg/ml), AKI, leukocytosis, abnormal electrolytes and LFTs. IV fluidsand antibiotics failed to improve the patient’s clinical status in 48 hours. He was started on IVthyroxine and stress steroids with improved weakness and overall clinical picture. Discussion: 4.6 % of people have hypothyroidism per the United States National Health andNutrition Examination Survey. Rhabdomyolysis is defined as the rapid breakdown of skeletal muscle,which may also develop due to hypothyroidism. Most patients with hypothyroidism who developrhabdomyolysis are found to have a clear precipitating risk factor, such as the use of statins orstrenuous exercise. Still, none of these risk factors were present in this case. Our patient acquiredhypothyroidism after a few months of receiving Immunotherapy. It is reported that hypothyroidismoccurs in (9% to 18%) of patients receiving Pembrolizumab. Although the patient was prescribedthyroid replacement therapy, he was not adherent to the medication for 1 month prior topresentation. Although mechanical injury is reported to cause elevated CK levels, mostrhabdomyolysis cases are related to crush injuries. We believe that the fall was probably related tohis progressive generalized weakness due to his noncompliance with medical therapy leading tomyxedema coma and rhabdomyolysis. Conclusion: Screening for hypothyroidism in patients with elevated muscle enzymes should behighly considered since an early diagnosis. Prompt treatment of hypothyroidism is essential toprevent rhabdomyolysis and its consequence.