5103 Synthroid Absorption Conundrum: A Case Deciphered

Abstract

Abstract Disclosure: H. Nadeem: None. O. Alzohaili: None. Hypothyroidism is a disorder requiring lifelong Synthroid therapy. Untreated patients have high morbidity rate and suffer from weight gain, cold intolerance, fatigue and constipation. Inadequate therapeutic outcomes may result in the case of malabsorption, like GI tract conditions, medication interactions and dietary ingredients. Here, we describe the case of a 50-year-old woman who despite compliance to therapy, had refractory hypothyroidism. Complexity of unexplained Synthroid malabsorption is highlighted, emphasizing the importance of managing and optimizing thyroid hormone replacement therapy. A 50-year-old woman with a history of papillary carcinoma s/p thyroidectomy and radioactive iodine therapy came in with fatigue, weight gain and constipation. Despite taking Synthroid 150 mcg, thyroid function tests (TFTs) remained high with TSH 150 uIU/mL and fT4 0.25 ng/dL. Her dose was gradually increased until it reached 1800 mcg yet repeat TFTs showed refractory hypothyroidism with TSH 179 uIU/mL, fT4 0.8 ng/dL. Compliance was addressed to which she demonstrated strict adherence, while avoiding concurrent intake of food, supplements or medications interfering with the absorption. Autoimmune conditions were ruled out and no dietary patterns affecting absorption were identified. A thyroid absorption test was then performed, during which 2100 mcg of Synthroid were given orally in the AM, and thyroid hormones were measured for 8 hours. She was found to have a TSH in 200s uIU/mL and fT4 <0.10 ng/dL, deeming her to have refractory hypothyroidism. She was seen by GI and had an EGD/ colonoscopy, revealing no abnormalities. In a follow up visit, she was still complaining of the same symptoms, periorbital edema, and mild confusion. Her TSH was still elevated at 225 uIU/mL. She was then started on IV 500 mcg of weekly Synthroid infusions and after several weeks, she reported symptoms improvement. Subsequent TFTs showed a progress in TSH, now 26.6 uIU/mL, with fT4 1 ng/dL, indicating successful management of Synthroid malabsorption. During this process, she had a nutritional assessment and was consistently having hyperlipidemia with LDL 243 mg/dL. She was compliant with Praluent and max dose of atorvastatin 80 mg, but LDL only decreased to 134 mg/dL after adjusting her thyroid hormone levels. With nonadherence being the top cause of medication non responsiveness, ruling out causes of malabsorption is vital. In this case, compliance, nutritional assessment, medication interactions, GI abnormalities, autoimmune conditions were all addressed and no interfering factors were identified. IV treatment with unexplained thyroid hormone malabsorption was the effective treatment, ultimately improving outcomes. With the hope to transition her to oral medication, the possibility of it happening is still not clear. More research is necessary to discover the underlying causes in such an exceptional case. Presentation: 6/2/2024