Thyroid Autoimmunity in Subjects with Type 1 Diabetes Mellitus: An Analysis of Prevalence Within a Defined Geographical Area in Sicily, Italy

Introduction

Thyroid autoimmunity is the most prevalent immunological process affecting subjects with type 1 diabetes mellitus. The association between diabetes and thyroid autoimmunity has long been recognized in many populations: in several studies of children and adults with type 1 diabetes, a high prevalence of thyroid autoantibodies (8–44%) has been found as an indicator of autoimmune thyroid disease.1–10 Heterogeneity has been described in the natural history of thyroid autoimmunity in type 1 diabetes: it may be disclosed either at the onset of diabetes or during the follow-up. Most of the antibody-positive diabetic patients are clinically and biochemically euthyroid. It is uncertain how many of them will later develop thyroid dysfunction but long-term follow-up suggests that the majority of type 1 diabetic patients with positive thyroid antibodies will develop hypothyroidism;10 hyperthyroidism is much less commonly reported.11, 12

Abstract

BACKGROUND

Thyroid autoimmunity is the most prevalent immunological process affecting subjects with type 1 diabetes. Aim of this work was to investigate thyroid autoimmunity in a large cohort of type 1 diabetic subjects all coming from a defined geographical area.

METHODS

Data were analyzed from 374 patients who were treated in a diabetes center in western Sicily (Italy), over a 2.5 year period. TPO-Ab, TSH, FT3, and FT4 were measured and documented at least once in all these patients.

RESULTS

During the period of the survey TPO-Ab were present in 108 patients, resulting in an overall prevalence of 28.8%; the female-to-male ratio was > 2:1. TPO-Ab+ patients showed an age at diabetes onset significantly higher. The thyroid status of most of these patients was euthyroidism (54 subjects) but overt hypothyroidism (38 subjects), subclinical hypothyroidism (13 subjects), and hyperthyroidism (three subjects) were also present. Subjects with overt hypothyroidism were significantly older than others and showed an age at diabetes diagnosis higher than euthyroid subjects.

CONCLUSIONS

Our data confirm the strong association between thyroid autoimmunity and type 1 diabetes in a Sicilian population. Therefore, in type 1 diabetic patients, an active search for the presence of autoimmune thyroiditis is warranted, particularly in female subjects.

Keywords

type 1 diabetes mellitus, autoimmune thyroid disease, thyroid autoimmunity