Thyroid autoimmunity in adults with diabetes mellitus type 1. Own experience gained by 11-year monitoring

The results of study on thyroid autoimmunity and its clinical importance gained during 11-year follow-up of 47 adults with type 1 diabetes mellitus (DM1) are presented. The study proved the preponderance of women among subject affected with thyroid autoimmunity, the autoantibodies against thyroid gland (T-Ab) were significantly more often detected in women compared to men (68% vs. 32%, p < 0.05). Also, serious forms of thyroid autoimmunity manifested with persistence of both T-Ab, faster development of subclinical hypothyroidism (TSH > 4.5 mIU/l in 100% within 4 years after first detection of T-Ab positivity, and within 8 years after DM1 manifestation, respectively), and diffuse hypoechogenic pattern at thyroid gland ultrasonography (USG) were significantly more often observed in women compared to men (45% vs. 12%, p< 0.01). These patients often had small thyroid gland (77% of subjects had volume below 25th percentile of control subjects at the 11th year of follow-up) and presence of thyreopathy in the first degree relatives. No difference between men and women was observed in persistence of thyroid peroxidase autoantibodies (anti-TPO) solely (20% vs. 23%); milder clinical course of thyroid disease was observed in these subjects (the fist detection of TSH > 4.5 mIU/l in the 9th year of follow-up). These patients had varied findings at USG examination with focally/diffuse hypoechogenic/ non-homogenous thyroid gland, and 50% of subjects had thyroid gland volume above 95th percentile in the 11th year of follow-up. Among subjects without thyroid autoimmunity men prevailed (68% vs. 32% women, p < 0.01), and in the 11th year of follow-up the USG finding was often abnormal (thyroid gland volume above 95th percentile of the controls in more than 60% of subjects, trend towards nodulisation). Except for 1 subject, TSH did not exceed 4.5 mIU/l. These results obtained from the Czech population constitute the basis for our recommendation to screen regularly markers of thyroid autoimmunity in patients with DM1. Ultrasonographic examination, that is able to detect sings of thyroid immunopathy in many subjects before first manifestation of T-Ab, is the most sensitive according to both our experience and the published data. For clinical practice, determination of TSH once a year in all DM1 subjects, and of anti-TPO in DM1 women in fertile age is recommended. Ultrasonographic examination should be carried out in case of pathologic results of these tests.

Keywords: diabetes mellitus, type 1; thyroid autoimmunity; thyroid gland autoantibodies; autoimmune thyroiditis; thyroid gland function; thyroid gland ultrasonography