This is a case of a 25 year-old male, with no known comorbidities, who presented with a 9-day history of bilateral arm pain which started after doing a pull-up exercise consisting of 3 sets of 10 repetitions with 60-90 seconds rest between. He regularly plays golf and goes to the gym once a week. He was not dehydrated, and denied intake of protein supplementation, statins and heavy carbohydrate meals before exercise. There were no other muscle pains, hematuria and decrease in urine output. He initially took Ibuprofen 200mg, however there was persistence with increase in severity of symptoms PS 10/10, hence sought ER consult. On admission, he had normal vital signs, with tenderness on bilateral arm. On physical examination, he was found to have exophthalmos, and a symmetric, smooth, and diffuse goiter (WHO Grade II). No thyroid bruit was heard.

Laboratory evaluation showed normal electrolytes (Na 140 mmol/L and K 4 mmol/L) and renal function (creatinine 0.67mg/dL eGFR 137) . Serum creatinine kinase-MM was elevated at 20, 126 (35- 232) U/L. Urine dipstick test was positive for blood. Thyroid function test showed suppressed TSH 0.01 uIU/mL and elevated FT4 5.13 (0.89-1.76) ng/dL and FT3 17.19 (2.30-4.20) pg/mL. The overall findings suggested rhabdomyolysis secondary to a single bout of regular exercise in a hyperthyroid state

Patient received aggressive fluid resuscitation and was started on Methimazole 20mg/tab BID and Propranolol 20mg/tab OD. His symptom significantly improved and serum creatinine kinase level gradually decreased without electrolyte imbalance or acute kidney injury after 5 days. The patient was discharged home with stable condition and had a radioactive iodine uptake done demonstrating high radioactive iodine uptake with homogenous activity consistent with Graves’ disease.

Hyperthyroidism, although rare, may cause rhabdomyolysis by means of cellular hypermetabolism associated with depletion of muscle energy stores and substrates. Currently, there have only been 7 reported cases of rhabdomyolysis as a result of thyrotoxicosis. We are reporting the 1st case of such association in the Philippines. Hence, in patients who developed rhabdomyolysis, hyperthyroidism should be considered in the differential diagnosis. This case highlights the importance of recognizing and addressing thyroid dysfunction in individuals presenting with rhabdomyolysis, ensuring timely and appropriate management.