MON-359 Graves Disease Treatment: When Pandora’s Box Was Just a Pill Away

Abstract Disclosure: F.J. Lopez Maldonado: None. E.R. Leon Milan: None. A. Rodriguez Gonzalez: None. A.A. Mayorga León: None. F. Hernandez Bravo: None. Introduction: Graves' disease is an autoimmune disorder characterized by hyperthyroidism, commonly treated with antithyroid medications such as methimazole and 5-propylthiouracil. Although effective, these drugs can cause severe adverse effects. Clinical Case A 47-year-old woman presented with a one-month history of distal fine tremor, tachycardia, insomnia, anxiety, heat intolerance, and a 10 kg weight loss. She also reported proximal muscle tenderness and weakness, consistent with thyroid myopathy. The symptoms progressively worsened, affecting her daily activities. She consulted her family physician, who ordered a thyroid profile that confirmed biochemical hyperthyroidism. Treatment with 10 mg of methimazole every 8 hours and 20 mg of propranolol every 12 hours was initiated, leading to an improvement in her symptoms. However, 3 days later, painful, erythematous, and nodular skin lesions appeared on both arms, legs, and abdomen, progressively spreading. The patient reported that initially, the lesions were isolated but quickly extended to other areas of the body. Despite treatment with antihistamines and steroids, no improvement was observed. She was evaluated by an endocrinology specialist, who found persistent tachycardia, fine distal tremor, insomnia, goiter, mild exophthalmos, and ongoing proximal muscle tenderness and weakness. On skin examination, erythematous and violaceous lesions were identified on the forearms, thighs, and lateral abdomen, symmetrically distributed. These lesions varied in size, from papules to nodules measuring 0.5 to 1 cm, with a tendency to coalesce and form plaques. In areas of greater congestion, petechiae and small bruises were observed.Laboratory tests showed the following thyroid profile:TSH: <0.01 µU/mL (0.4-4.0 µU/mL)Free T4 (T4L): 3.2 ng/dL (0.9-1.7 ng/dL)Total T3 (T3T): 320 ng/dL (80-200 ng/dL)TRAb: 15 IU/L (<1.75 IU/L) Given this clinical presentation, methimazole was discontinued, treatment with Lugol's solution was initiated, and a skin biopsy was performed. Histopathological study confirmed the presence of small-vessel lymphocytic vasculitis consistent with leukocytoclastic vasculitis. After discontinuing methimazole, the skin lesions resolved. The patient subsequently underwent total thyroidectomy and began levothyroxine replacement therapy. After one year of follow-up, there has been no recurrence of the skin lesions. Conclusion: This case underscores the need for close monitoring of adverse reactions when treating Graves' disease with antithyroid medications. Leukocytoclastic vasculitis, induced by methimazole and 5-propylthiouracil, is a rare but serious complication that may require prompt changes in treatment or surgical intervention. Presentation: Monday, July 14, 2025