When Thyroxine Isn’t Enough: Coeliac Disease as a Silent Contributor to Treatment-Resistant Hypothyroidism

Abstract

Background: Refractory hypothyroidism, characterized by persistently elevated thyroid-stimulating hormone (TSH) levels despite high-dose levothyroxine therapy, necessitates a thorough evaluation for underlying causes. While noncompliance is a common reason, it must be carefully excluded before considering alternative explanations such as malabsorption syndromes. Coeliac disease is a known but often under-recognized cause of levothyroxine malabsorption.

Case Presentation: We report the case of a 15-year-old girl with a 3-year history of primary hypothyroidism who presented with persistently elevated TSH levels (>30 mIU/L) despite daily administration of 250 mcg levothyroxine per day. She demonstrated full compliance with medication, proper intake technique, and no interfering drugs or supplements. Her low body weight (35 kg) and disproportionate levothyroxine requirement raised suspicion for malabsorption. Serologic testing revealed positive tissue transglutaminase IgA antibodies, confirming the diagnosis of coeliac disease.

Management and Outcome: The patient was commenced on a strict gluten-free diet. Within months, her TSH levels declined, levothyroxine dose requirements dropped to 50 mcg/day, and her weight increased to 42 kg. Her most recent TSH is 1.3 mIU/L reflecting euthyroidism.

Conclusion: This case highlights the importance of considering coeliac disease as a cause of refractory hypothyroidism when noncompliance and administration errors have been clearly excluded. Identifying and treating the underlying malabsorption with a gluten-free diet can significantly reduce hormone requirements and restore euthyroidism.