Endocrine Abstracts

Introduction: Thyroid hormones are involved in the development of the fœtus and the child, and abnormal thyroid function is expected to play a role in neurodevelopmental disorders such as Attention Deficit with Hyperactivity Disorder (ADHD). The high prevalence of ADHD in patients with resistance to thyroid hormone syndrome is well documented but, surprisingly, the reported literature showed ambiguous results mostly suggesting that the thyroid function tests are normal in the majority of patients with ADHD. However, it is possible to pinpoint a number of methodological and analytical limits in the thyroid evaluation of patients in the studies. Here we report on the prevalence of isolated and increased free-T3 level in the presence of normal free-T4 and TSH levels in children with ADHD.

Methods: Serum free-T3, free-T4 and TSH levels were measured in children referred to the first author (HC) in the last two decades and diagnosed with ADHD. No control was possible on the analytic methods as thyroid function tests were performed in town laboratories.

Results: Out of 1.967 patients, 701 children with ADHD (boys n=562, girls n=139) between 6 and 18 years old had complete thyroid function tests (free-T3, free-T4 and TSH levels). According to the reference intervals noted in laboratory reports, a TSH level was abnormal in 16 patients (2.28%): 2 decreased TSH level with normal free-T3 and free-T4 level, 14 increased TSH level with either normal or elevated free-T3 and/or free-T4. Out of the 685 normal-TSH remaining patients, 435 (63.50%) had a normal thyroid profile, and 217 (31.68%): 180 boys (32.67%) and 37 girls (27.61%) showed an isolated and increased free-T3 level. There was no effect of gender: χ² (1)= 0.677 (P>.4).

Discussion: In children with ADHD, an isolated and increased free-T3 level is frequent and unrelated with gender. This result should be further confirmed and documented. If so, this abnormal thyroid profile may constitute an endophenotype for a significant proportion of children with ADHD, and yield to new pathophysiological hypotheses in the neurodevelopment disorders.

Conclusion: Abnormal thyroid function tests are not rare in children with ADHD, more specifically we highlighted an isolated and increased free-T3 level with normal free-T4 and TSH levels in up to one third of children with ADHD. These results warrant confirmation; this is the main objective of the on-going prospective “ThyrADHD” study (NCT05080491).