SAT478 A Rare Case of Thyrotoxic Periodic Paralysis in a Patient with Concomitant Methimazole-Induced Agranulocytosis

Disclosure: K.S. Wei: None. S.M. Cannon: None. T.E. Angell: None. Introduction: Thyrotoxic state may precipitate sudden-onset unilateral or bilateral extremity weakness brought on by transient hypokalemia requiring specific management. Clinical Case: A 48-year-old woman presented to our hospital with fevers, sore throat, and sudden-onset bilateral leg weakness. Ten weeks prior, she was started on methimazole 20mg daily for a new diagnosis of Graves’ disease. Two days prior to presentation, she had consumed a carbohydrate-heavy meal and that night experienced acute-onset lower extremity weakness rendering her unable to walk. She also had been experiencing sore throat, odynophagia, and intermittent fevers. On admission, the patient was found to be febrile, tachycardic, and in shock with WBC <0.5 (ref: 4.5-10 K/cumm), potassium 2.6 (3.5-5.1 mmol/L), lactate 4.1 (0.5-2.2 mmol/L), TSH <0.01 (0.27-4.2 uIU/mL), fT4 4.04 (0.93-1.7 ng/dL) and was admitted to the ICU for neutropenic fever and septic shock. Computed tomography (CT) imaging of the thorax showed right lung consolidation suggesting pneumonia. Magnetic resonance imaging of the spine and CT head did not demonstrate an etiology for her weakness. She was diagnosed with thyrotoxic periodic paralysis (TPP) and treated with potassium. For severe hyperthyroidism with methimazole contraindication, she received broad spectrum antibiotics, lithium 300mg orally every 8 hours, and propranolol 10-20mg every 8 hours. Given minimal improvement in both weakness and hypokalemia after 48 hours of therapy, she was also diagnosed with refeeding syndrome and potassium repletion was intensified. The patient’s shock resolved, with slow improvement of lower extremity weakness over a two-week period and resolution of agranulocytosis and fevers. Conclusion: This rare presentation offers several distinct points regarding the patient’s care. Firstly, TPP is a rare hyperthyroidism-related hypokalemia that can cause weakening of the extremities due to a rapid intracellular shift of potassium (1) and is an important syndrome to consider on the differential for any thyrotoxic patient presenting with sudden-onset weakness. Secondly, gentle potassium repletion is recommended to prevent rebound hyperkalemia. However, our patient had both total body loss of potassium from refeeding syndrome and intracellular shift from TPP, requiring more aggressive potassium repletion to treat her paralysis than is typical for TPP alone. In settings where weakness and hypokalemia do not improve with beta blockade and gentle potassium repletion, it is important to investigate other causes of hypokalemia and consider concurrent overlapping diagnoses. Lastly, patients with methimazole-induced agranulocytosis may require alternative treatments, such as lithium to control hyperthyroidism. 1) Lin, Shih-Hua. Thyrotoxic Periodic Paralysis. Mayo Clin Proc. 2005;80(1):99-105. Presentation Date: Saturday, June 17, 2023