ACTH-Secreting Pituitary Adenoma in Setting of Addison’s Disease: A Case Report and Literature Review

Objective To describe the development and outcome of an ACTH-secreting pituitary adenoma in a patient with long-standing Addison's disease, and to review the existing literature on this rare entity. Methods We report the clinical presentation, biochemical findings, imaging, and clinical course of a patient with Addison's disease who developed an ACTH-secreting pituitary adenoma complicated by pituitary apoplexy. ACTH and cortisol were measured by chemiluminescence immunoassays, and ACTH precursors were measured by ELISA. A comprehensive literature review was performed to identify similar cases. Results A 76-year-old woman with Addison's disease diagnosed 41 years prior presented with progressive hyperpigmentation and was found to have markedly elevated ACTH levels (14,717–67,220 pg/mL; reference range 8–42 pg/mL) and a sellar mass measuring 1.8 × 1.9 × 1.9 cm on MRI. The patient subsequently experienced pituitary apoplexy with dramatic reduction in ACTH levels to 323–2,035 pg/mL and decrease in tumor size. To the authors' knowledge, this represents the first reported case of pituitary apoplexy occurring in an ACTH-secreting adenoma arising in the setting of non-surgical primary adrenal insufficiency. A review of the literature identified six confirmed and several additional suspected cases of ACTH-secreting pituitary adenoma in the setting of non-surgical primary adrenal insufficiency. Conclusion ACTH-secreting pituitary adenoma in the setting of non-surgical primary adrenal insufficiency is a rare but important condition. Persistent hyperpigmentation or markedly elevated ACTH despite adequate glucocorticoid replacement should raise suspicion for this entity. Management includes optimization of glucocorticoid replacement and surgical intervention when mass effect is present. Additionally, as demonstrated in the present case, pituitary apoplexy may occur and can result in significant reduction in tumor size and ACTH secretion.