P-125 WHEN PILLS FAIL: REFRACTORY HYPOTHYROIDISM MANAGED WITH INTRAVENOUS AND SOFT-GEL LEVOTHYROXINE

Abstract Introduction The standard first-line treatment of hypothyroidism is oral levothyroxine (LT4) tablets usually at a dose of 1.6-1.8 μg/kg/day. Refractory hypothyroidism (RH) is defined as persistently elevated thyroid-stimulating hormone (TSH) levels despite LT4 doses ≥1.9 μg/kg/day, irrespective of symptoms. RH poses a clinical challenge due to diagnostic complexity, lack of clear guidelines, and risk of overtreatment. We report a case of RH successfully managed with intravenous (iv) LT4 and transitioned to soft-gel capsule LT4, resulting in sustained euthyroidism. Clinical Case A 48-year-old woman with multinodular goiter underwent subtotal thyroidectomy for hyperthyroidism. Histopathology revealed a 1-cm encapsulated follicular variant papillary thyroid carcinoma. LT4 was started at 25 µg/day. Over the next 2 years, despite dose escalation up to 400 µg/day, she remained symptomatic with TSH levels between 30–96 mIU/L and fT4 ranging 2.5-6 pmol/L. Oral liothyronine and various LT4 formulations failed to improve thyroid function. Endoscopy revealed eosinophilic pangastritis; anti-endomysial antibodies were positive, but a gluten-free diet did not restore euthyroidism. At our center, she presented on LT4 800 µg/day with persistent hypothyroidism (TSH 82 mIU/L, fT4