THU012 Incidental Pituitary Adenoma In A Patient With Ectopic ACTH Secreting Cushing Syndrome - A Diagnostic Conundrum

Abstract

Abstract Disclosure: M.S. Nali: None. R.R. Yatavelli: None. Background: Cushing’s syndrome (CS) is a rare condition with an estimated incidence of 2-3 cases/million. Endogenous CS can be divided into ACTH -dependent (80%) and ACTH Independent (20%) with Ectopic Cushing’s syndrome (ECS) accounting for 10-20% of all cases of ACTH-dependent CS. Herein we present a case with indolent onset ACTH-dependent CS who on initial work-up showed a pituitary microadenoma raising the suspicion for Cushing disease, but the source of excess ACTH was found to be from a pulmonary neuroendocrine tumor. Clinical Case: A 44-yr-old female with history of type 1 DM, Obesity, BMI 43.60, Sleep apnea was evaluated elsewhere for suspected Cushing’s due to increased insulin requirements and progressive weight gain. Outside labs showed cortisol of 4.5 ug/dl on 1 mg DST & 8 mg DST cortisol was 3 ug/dl. MRI of the pituitary showed a 3.5x 2.8x 1.8 mm microadenoma & she was initially presumed to have Cushing’s disease secondary to pituitary microadenoma. The patient was seen by neurosurgery who referred to endocrine for localization of cortisol excess by IPSS. Clinically she had moon facies, hirsutism, dorsocervical fat pad, violaceous striae on abdomen. On further laboratory evaluation her ACTH: 88 (0-46) and random cortisol 14 ug/dl with normal rest of pituitary hormones. Her 24-hour urine free Cortisol was 45ug/d (3.5 - 45) and late-night salivary cortisol: 74 &<50 (Ref. range <100 ng/dl) on couple of nights, respectively. Due to non-suppressed cortisol on high dose DST, a CT chest was obtained which showed a 2cms non calcified nodule in the left lower lobe of lung. Transbronchial biopsy was performed, cytopathology showed well differentiated neuroendocrine tumor, likely carcinoid and stained strongly positive for ACTH confirming ectopic ACTH producing tumor. Gallium-68 Dotatate Scan showed abnormal increased uptake in the known left lung nodule. The patient was recommended for surgical removal of neuroendocrine tumor, but she could not tolerate anesthesia and had to undergo stereotactic body radiation therapy (SBRT) for the lung lesion. Repeat ACTH levels 2 months post SBRT showed the ACTH levels were elevated and lesion was still persistent on imaging, however on discussion with rad oncology, the neuroendocrine tumors tend to take longer to show response on imaging and plan is to repeat imaging and biochemical work up in couple of months. Conclusion: The diagnosis of CS and recognizing the source of hormonal excess poses significant challenges Pituitary adenomas are incidentally discovered in up to 10% of the normal population & IPSS is advised for patients with ACTH-dependent Cushing's syndrome and an adenoma smaller than 6 mm, however in patients with equivocal findings, it is important to look for other sources of ACTH prior to any invasive procedure. The source of ectopic ACTH secretion should be established after diagnosis because the excision of an ACTH-producing tumor can be curative. Presentation: Thursday, June 15, 2023