8183 An Unusual Cause of Fluctuating Thyroid Hormone Levels

Abstract Disclosure: V. Taqi: None. W. Akhter: None. J.L. Gilden: None. Background: Thyroid disease, especially congenital hypothyroidism is a common endocrine problem with an estimated global prevalence of 4.25%. Since every organ system is affected by thyroid hormones, untreated hypothyroidism can lead to profound adverse outcomes. Many drugs, hormones, and dietary supplements have been noted to affect the efficacy of thyroid hormones, yet there was always concern about the effect of the excessive growth of intestinal flora in the small intestine on thyroid supplement absorption. Drugs, malabsorption, celiac disease and increased excretion are common causes of fluctuating thyroid hormones. In this case, we present a young male patient with congenital hypothyroidism, who required fluctuating doses of levothyroxine due to abnormal thyroid hormone levels, despite compliance with proper administration, and dramatic improvement of thyroid hormone levels after starting probiotic therapy. Case : An 18-year-old Caucasian male with congenital hypothyroidism had been treated with varying doses of thyroid hormone replacement by a Pediatric Endocrine Center. Due to his recall that TSH=4.13 mIU/L and he was “tired of taking medication”, he stopped taking 125 mcg of levothyroxine. Four months later, TSH was > 200 mIU/L (nl=0.48-4.17). Levothyroxine 137 mcg was then started. However, 11 months later, TSH=14.2 mIU/L, Free T4=1.6 ng/dL (nl=1.03-1.64). He was then referred to our Endocrine Clinic. He denied symptoms of hypo or hyperthyroidism or other medical issues. His grandfather was known to have hypothyroidism and diabetes mellitus (details unknown). On exam: Wt. was 149 Ib, Ht= 67 Inch. VS: BP 98/46, P 69, R:16,temp: 97.9F, Physical exam showed normal findings without thyromegaly, but there was a delay in tendon reflexes. Laboratory-unremarkable CBC, CMP panels with normal thyroid antibodies, and Celiac titers. TSH initially improved from 14.2 to 8.4 mIU/L after increasing the thyroxine dosage from 137 to 150 mcg for 2 weeks, then to 175 mcg after 4 weeks, but TSH increased to 12.1 mIu/L, despite being compliant with medication and ensuring proper way of administration. He continued to deny symptoms of hypo or hyperthyroidism, or any other medical issues, including lactose intolerance or malabsorption. However, probiotics were then added to his regimen, and continuation of the current dose resulted in a suppressed TSH=0.15 mIU/L. The levothyroxine was then decreased to 150 mcg with continuation of probiotics. One month later, TSH was 1.31 mIU/L with Free T4 of 1.5 ng/dL. Conclusion : Common causes for fluctuating thyroid hormone levels include intestinal malabsorption, celiac disease, nephrotic syndrome, drugs, and food interaction. This case demonstrates that despite proper administration, fluctuating thyroid hormone levels can result from some uncommon causes, such as lactose intolerance, which can be unmasked by co-administration of probiotics. Presentation: 6/2/2024