Increased prevalence of thyroid autoimmunity in patients successfully treated for Cushing's disease

BACKGROUND. Cushing's disease is characterized by abnormalities of immune function. OBJECTIVE. To evaluate the prevalence of autoimmune thyroid diseases in patients with Cushing's disease (CD), after successful treatment and the possible association between previous nodular goitre or positive thyroid autoantibodies during the active phase of CD and the subsequent development of autoimmune thyroid diseases after cure. SUBJECTS AND METHODS. Twenty patients with CD and 40 sex- and age-matched healthy controls were considered for the study. In CD patients, thyroid ultrasonography and measurement of circulating free thyroxine (fT4), free triiodothyronine (fT3), thyroid stimulating hormone (TSH), antithyroglobulin (anti-Tg) and antithyroperoxidase (anti-TPO) antibodies were performed at diagnosis and 6 months after disease cure while in controls they were performed only at study entry. RESULTS. Serum fT3, and fT4 levels were similar in patients, either during the active phase or after cure of the disease, and controls. Conversely, in the patients, serum TSH levels were significantly lower during active disease (0.4±0.05 mU/l, P=0.001) and significantly higher after disease cure (4.7±0.1 mU/l, P<0.001) than in controls (2.3±0.4 mU/l). Four patients (20%) and 11 controls (27.5%) had positive anti-Tg and/or anti-TPO titre at study entry, while eight patients (40%) developed positive anti-Tg and/or anti-TPO titre after disease cure. The prevalence of positive antithyroid antibodies titre in cured CD patients was significantly higher than that observed in the same patients during the active disease (P=0.008) and in controls (P=0.031). A significantly higher prevalence of autoimmune thyroiditis was found in patients cured from CD (35%) than in patients with active CD (0%) (P=0.016) and in controls (10%) (P=0.031). A significant association was found between the presence of autoimmune thyroiditis after CD cure and the presence of a previous nodular goitre (P=0.017) or positive thyroid autoantibodies titre (P=0.007) during the active phase of the disease. CONCLUSION. Patients successfully treated for Cushing's disease have an increased prevalence of thyroid autoimmunity and autoimmune thyroiditis as compared to a control population. Therefore, patients with hypercortisolism need an accurate evaluation of thyroid function after remission of the disease in order to prevent the eventual onset of subclinical or overt post-thyroiditis hypothyroidism