Thyroid autoimmunity in children and adolescents with type 1 diabetes mellitus: prevalence and risk factors.

Unlabelled: Studies show great variation in prevalence of anti-thyroid antibodies in children with type 1 diabetes mellitus (DM1). There still is no consensus regarding screening of autoimmune thyroiditis in patients with DM1, especially in asymptomatic patients.

Aim: To investigate the natural history and prevalence of autoimmune thyroiditis in pediatric patients with DM1 and relate it to potential risk factors.

Patients And Methods: This study is a historical cohort, through research of the records of 474 patients with DM1 from 9 months to 25 years of age, between 1980 and 2005 - 222 boys (46.8%) and 252 girls (53.2%), with an average duration of DM1 of 9.3 +/- 5.8 years. The sample was selected by having at least one measurement of TSH and anti-thyroid autoantibodies (antithyroperoxidase or anti-microssomal and/or anti-thyroglobulin) at any time from diagnosis of DM1. A questionnaire was answered in order to study the variables of interest for the study. Thyroid function disorder was defined as altered levels of TSH, with or without altered free T4 levels.

Results: A total of 383 patients (9 months to 25 years of age) were studied, 199 girls (52%) and 184 boys (48%). Sixty-four (16.7%) had positive anti-thyroid antibodies, predominantly girls (p = 0.064). Average duration of DM1 was 9.3 +/- 5.8 years and those above this age had a higher incidence of thyroiditis (p = 0.01). The prevalence of thyroid function disorder in patients with DM1 was 7.3% (n = 28), mostly with thyroiditis (32.8% vs 2.2% with negative antibodies, p < 0.001). There was a positive association between thyroiditis, as well as thyroid function disorders, and other autoimmune disorders (p < 0.001 and p < 0.02, respectively).

Conclusions: Prevalence of thyroiditis in the diabetic population is considerably higher than in the general population. Annual laboratory determinations of anti-TPO antibodies and dosage of TSH should be part of routine tests in the diabetic population, especially in girls, children with DM1 for > 9 years, patients above 12 years of age, and those in whom DM1 is associated with another autoimmune disease. Anti-thyroid antibody positivity may indicate the necessity for thyroid function testing at shorter intervals.