Abstract: Gastrointestinal disorders may impair oral thyroxine (T4) absorption by either affecting the tablet dissolution or adsorbing the hormone in the first tract of intestinal lumen. Ulcerative colitis (UC) is an inflammatory disease whose interference with oral T4 treatment has been suggested but no evidence have been presented so far. This study was aimed at examining the presence of UC and its possible interference in the pharmacologic thyroid homeostasis, in a large cohort of patients with thyroid disorders. Among 8573 outpatients with thyroid disorders we recruited 34 patients with a definite diagnosis of UC. We selected them using these inclusions criteria: a) hypothyroidism due to Hashimotos thyroiditis (HT); b) at least two years of thyroxine treatment using the same dose and brand; c) TSH values between 0.8 and 2.5 mU/l in at least three subsequent control visit; d) ulcerative colitis in a stable remission phase. According with the policy of our Centre, all patients enrolled in the study have pledged to take T4 in a tightly controlled fashion and we checked their compliance with the treatment by interviewing them. Patients non compliant or treated with drugs interfering with thyroid homeostasis and/or bearing chronic, infectious, inflammatory or neoplastic diseases had been also excluded. Overall, only 13 of them (12F/1M; median age=53years) met the criteria and were included in the study group. To calculate the possible excess of T4 required, we compared the minimal effective dose of T4 the UC patients to the one observed in 51 similarly treated age- and weight-matched HT patients, clearly devoid from gastrointestinal and/or pharmacological interference. Twelve out of 13 patients (92%) with HT and UC, required a dose of T4 higher than in the control patients to reach target TSH. Therefore even the median T4 dose required by UC patients was 26% higher (1.54 vs 1.23 μg/kg weight/day; P=0.0002). Since half of our study group consisted of patients aged over 60 years and elderly patients usually require a reduced T4 dose, we reanalyzed our data after their subdivision in two classes of age. Six out of seven (86%) adult patients (<60 years) required a higher T4 dose (1.61 vs 1.27 μg/kg weight/day;+27%, P<0.0001) than the one in the control group. Similarly, all senior patients showed an increased need for thyroxine but to a lesser extent (1.25 vs 1.07 μg/kg weight/day;+17%, P=0.0026). Ulcerative colitis, even during clinical remission, may represent a novel cause of increased need for oral thyroxine.
18 May 2019 - 21 May 2019