Delayed Detection of ACTH-Secreting Pituitary Microadenoma: A Case for Serial Imaging in Refractory Cushing’s Disease

Cushing’s disease (CD), a subtype of Cushing syndrome caused by pituitary ACTH-secreting adenomas, can be challenging to diagnose, especially in the presence of adrenal incidentalomas which can suggest adrenal cause shifting the focus away from the possibility of true pituitary disease in ACTH-dependent hypercortisolism. Case Presentation This case is presented as a 61-year-old female with an initial presentation of hypercortisolism who was diagnosed with adrenal Cushing syndrome after an MRI revealed a unilateral adrenal incidentaloma. She was gonadotrophically deprived and her adrenal gland was removed and she briefly improved. The symptoms reoccurred several years later and repeat imaging and inferior petrosal sinus sampling (IPSS) showed that she had an ACTH-secreting pituitary microadenoma. After transsphenoidal resection, the IGF-I of the patient was slightly elevated that created the suspicion of GH co-secretion even though there was no clinical sign of acromegaly. The patient has attained biochemical remission and she is under close follow up. Conclusion This case highlights the diagnostic complexity of CD in the presence of adrenal incidentalomas and emphasizes the importance of thorough hormonal workup, repeat imaging, and the use of IPSS. The deviation from the diagnostic guidelines for biochemistry and failure to recognize the initial normal levels of ACTH could have eliminated the delayed diagnosis. Keywords: Cushing’s Disease, ACTH-secreting adenoma, GH co-secretion, pituitary tumor, adrenal incidentaloma, diagnostic delay