SAT-389 Graves’ Disease and Thyrotoxic Periodic Paralysis: A Case Series

Abstract Disclosure: J. Arguinchona: None. N. Allen: None. M. Vahidi Rad: None. K. Doshi: None. Background: Thyrotoxic periodic paralysis (TPP) is a distinct disorder characterized by episodic, generalized muscle weakness due to hypokalemia, occurring predominantly in young adult males (20-40 years) with hyperthyroidism, particularly Graves' disease. TPP is common in East Asian populations, affecting approximately 2% of individuals with hyperthyroidism, but is rare in Western populations (0.1-0.2%) and often underrecognized in the United States. Herein, we present three cases of TPP in young Hispanic and Caucasian males with Graves’ disease, underscoring the importance of diagnostic vigilance. Clinical Cases: Case 1: A 21 y.o. Hispanic male presented to endocrine clinic following multiple hospitalizations for severe hypokalemia and myopathy. During admission, labs showed a potassium (K) 1.2 mmol/L (3.6-5.2), undetectable thyroid stimulating hormone (TSH), and free thyroxine (FT4) 2.8 ng/dL (0.9-1.7). K was replaced and Graves’s disease was confirmed by positive TSH receptor antibodies. He was started on methimazole and subsequently underwent radioactive iodine (I-131) therapy. Following development of hypothyroidism, he was placed on levothyroxine replacement, with no further recurrence of paralysis. Case 2: An 18 y.o. Caucasian male with a history of Graves’ disease presented after multiple hospitalizations for hypokalemia and lower extremity weakness. Hospitalization labs showed a suppressed TSH, FT4 2.2 ng/dL, free triiodothyronine (FT3) 7.9 pg/mL (2.3-4.1), and K 2.8 mmol/L. His weakness improved with K replacement. Methimazole was initiated and the patient subsequently opted for total thyroidectomy for definitive therapy. No recurrence of TPP was observed after thyroidectomy. Case 3: A 29 y.o. Hispanic male with Graves’ disease, non-adherent to methimazole was hospitalized due to symptoms of diffuse upper and lower extremity weakness. Labs showed K 1.6 mmol/L, undetectable TSH, and T4 >7.7 ng/dL. Symptoms resolved with K replacement. He was restarted on methimazole as well as atenolol and advised on medical adherence. Unfortunately, he was lost to follow up, and re-hospitalized 7 months later with similar symptoms and labs, again due to nonadherence with thionamide medication. After aggressive K replacement and methimazole resumption, he was discharged with urgent endocrine follow-up for definitive management of Graves’ disease. Conclusion: These cases highlight the under recognition of TPP in non-Asian populations in the United States, leading to delayed diagnosis and recurrent hospitalizations. Clinicians should maintain a high index of suspicion for TPP in young males with hypokalemia, and generalized weakness, particularly in the setting of undiagnosed or untreated hyperthyroidism. Prompt recognition and definitive treatment of hyperthyroidism is critical to preventing recurrent episodes and associated morbidity. Presentation: Saturday, July 12, 2025