Atypical Thymic Carcinoid Associated with Ectopic ACTH Syndrome: Demonstration of ACTH secretion with ultrastructural and immunohistochemical studies

ABSTRACT

We reported a case of atypical thymic carcinoid tumor with ectopic ACTH syndrome which was proved by the presence of intracytoplasmic ACTH in the tumor cells using PAP method and electron microscopy. The patient was a 43-year-old housewife who was referred with Cushing's syndrome of unknown origin, and subsequantly followed by many disabling symptoms including, diabetes mellitus and electrolyte imbalance for which bilateral adrenalectomy was carried out. Thereafter, rapid rise in serum ACTH level and hyperpigmentation were followed. Pituitary irradiation was done under the impression of Nelson's syndrome despite of lacking evidence of pituitary tumor, but high serum ACTH persisted. Seven months after pituitary irradiation, two anterior mediastinal masses were first noticed and removed. Immunohistochemical and ultrastructural studies confirmed this neoplasm as a ACTH producing spindle cell variant of atypical thymic carcinoid tumor. When dealing with a patient who developed Nelson's syndrome-like phenomenon without apparent pituitary tumor, the possibility of ectopic ACTH syndrome caused by thymic carcinoid should be considered.