MON-359 - Thyrotoxic Periodic Paralysis: A Rare First Sign of Graves' Disease in A Young Patient

Introduction:
Thyrotoxic periodic paralysis (TPP) is a rare but potentially life-threatening complication of hyperthyroidism characterized by acute hypokalemia and reversible muscle weakness. Prompt recognition is essential, as delayed diagnosis can result in severe neuromuscular and cardiac complications. Our case demonstrates an example of TPP presenting with progressive weakness and profound hypokalemia, ultimately leading to a new diagnosis of Graves’ disease in our patient.

Case Presentation:
A 22-year-old male with a history of asthma, ADHD, and bipolar disorder presented with one month of progressive myalgias and weakness, which culminated in difficulty ambulating and an inability to move his extremities. He also had associated hand tremor, diaphoresis, irritability, weight loss, and shortness of breath with wheezing. Lab work revealed a critical hypokalemia of 1.7 mmol/L. The EKG showed normal sinus rhythm with a new incomplete right bundle branch block and prolonged QTc to 627 ms. The patient's potassium subsequently resulted as 5.6 mmol/L after only 100 mEq of repletion. This rapid correction is suggestive of transcellular shift rather than true total body depletion and raises concerns for rebound hyperkalemia. Thyroid function revealed an undetectable TSH with elevated free T4 of 3.01ng/dl (0.7-1.8) and Free T3 7.1 pg/ml (2.3-5). The patient was started on methimazole and atenolol, instead of propranolol due to asthma symptoms. TSI and TRAb antibodies were markedly elevated indicating Graves' disease as an etiology for his hyperthyroidism. With treatment, the patient’s symptoms of weakness had completely resolved along with his hypokalemia and EKG changes.

Discussion:
Our case is notable for a new diagnosis of Graves’ disease based on an initial presentation of reversible weakness and severe hypokalemia due to thyrotoxic periodic paralysis. The absence of overt thyrotoxic symptoms, such as in this case, may delay diagnosis and appropriate management. This case highlights the importance of considering TPP in the differential diagnosis of acute paralysis, particularly in patients with severe hypokalemia. Early recognition is critical to avoid unnecessary investigations and reduce the risk of cardiac and neuromuscular complications. It also highlights the importance of cautious potassium repletion, as this can lead to rebound hyperkalemia, given that total body potassium is typically normal.

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