Case report: silent thyroiditis after adrenalectomy in a patient with Cushing's syndrome

A case of silent thyroiditis after unilateral adrenalectomy for treatment of Cushing's syndrome is reported. The left adrenocortical adenoma was resected. Glucocorticoid was replaced after the operation and was gradually tapered. Thyrotoxic symptoms with painless goiter occurred 9 months after the adrenalectomy when a replacement dose of prednisolone was tapered to 5 mg/d. Plasma-free thyroid hormones increased and thyrotropin was suppressed. Thyroidal uptake of radioactive iodine was extremely low. Both titers of antimicrosomal and antithyroglobulin antibodies stayed at high levels throughout the observation period from the preoperative stage. Normalization of thyroid functions was obtained 3 months after the onset of thyrotoxicosis with beta-adrenergic blocker alone. It was speculated that exposure to a large amount of endogenous and supplementary exogenous glucocorticoid protected the patient's immune system from autoimmune attack of thyroid antigens and that tapering of the supplementary glucocorticoid caused exacerbation of immune responses, resulting in overt thyroid dysfunction even 9 months after adrenalectomy.