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

BACKGROUND Gushing's disease is characterized by abnormalities of immune fu nction. OBJECTIVE To evaluate the prevalence of autoimmune thyroid diseases in patients with Gushing's disease (CD), after successful treatment and th e 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 he althy controls were considered for the study. In CD patients, thyroid ultra sonography and measurement of circulating free thyroxine (fT(4)), free trii odothyronine (fT(3)), thyroid stimulating hormone (TSH), antithyroglobulin (anti-Tg) and antithyroperoxidase (anti-TPO) antibodies were performed at d iagnosis and 6 months after disease cure while in controls they were perfor med only at study entry. RESULTS Serum fT(3), and fT(4) levels were similar in patients, either duri ng the active phase or after cure of the disease, and controls. Conversely, in the patients, serum TSH levels were significantly lower during active d isease (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-T g and/or anti-TPO titre after disease cure. The prevalence of positive anti thyroid 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 thy roiditis was found in patients cured from CD (35%) than in patients with ac tive CD (0%) (P=0.016) and in controls (10%) (P=0.031). A significant assoc iation was found between the presence of autoimmune thyroiditis after CD cu re and the presence of a previous nodular goitre (P=0.017) or positive thyr oid autoantibodies titre (P=0.007) during the active phase of the disease. CONCLUSION Patients successfully treated for Cushing's disease have an incr eased prevalence of thyroid autoimmunity and autoimmune thyroiditis as comp ared to a control population. Therefore, patients with hypercortisolism nee d an accurate evaluation of thyroid function after remission of the disease in order to prevent the eventual onset of subclinical or overt post-thyroi ditis hypothyroidism.