MON-096 ACTH Secreting Neuroendocrine Tumor Presenting With Pneumocystis Jirovecii Pneumonia

Abstract Disclosure: P. Shah: None. J. Mcgee: None. Background Pneumocystis pneumonia (PJP) is a rare but serious complication of immunosuppression. Patients with neuroendocrine tumors, specifically those involving elevated cortisol levels, are uniquely susceptible to such opportunistic infections. Having a high index of suspicion as well as prompt recognition and treatment of PJP in patients with elevated cortisol is critical to reduce morbidity and mortality. Clinical Case A 49-year-old female with a recent diagnosis of ACTH-dependent Cushing syndrome presented initially with altered mental status. She had a recent admission at another hospital for hypokalemia and palpitations and underwent workup for hypercortisolism with dexamethasone suppression testing. The diagnosis of Cushing syndrome was confirmed with 1mg dexamethasone resulting in a cortisol of 61.68 mcg/dL (n < 1.8 mcg/dL) and ACTH of 388 pg/mL and 8 mg dexamethasone resulting in a cortisol of 122 mcg/dL and ACTH of 616 pg/mL. MRI brain was negative, and abdominal imaging was not performed. During this admission, CT chest abdomen pelvis showed a small pancreatic tail mass suspicious for a primary neoplasm, a large hepatic mass suspicious for metastasis, and diffuse nonspecific thickening of bilateral adrenal glands. Pathology results from EGD/EUS and biopsy of the pancreas and liver were consistent with a neuroendocrine tumor. Complications from the Cushing syndrome included new onset type 2 diabetes mellitus, HTN, muscle weakness, osteoporosis, hypokalemia, hyponatremia, and florid hallucinations. She was started on metyrapone and doses were titrated based on cortisol levels. After initiation of therapy, her course was complicated by acute hypoxic respiratory failure requiring 100%/60L high flow nasal cannula. She was found to have PJP, confirmed with positive sputum PJP PCR and elevated fungitell. The patient required high flow supplemental oxygen, a three-week course of Bactrim, and a decreased metyrapone dose to increase the effective steroid dose. Fortunately, her respiratory status eventually improved and she was discharged on room air, PJP prophylaxis, and metyrapone. Conclusion This case highlights the significant immunosuppressive effects of hypercortisolism predisposing patients to PJP, with mortality in such cases reported as high as 20%. Similar cases have shown the development of PJP after initiating cortisol-lowering treatments suggesting a component of immune reconstitution. Prophylaxis against PJP should be considered in patients with Cushing Syndrome before starting treatment, and awareness for clinical PJP should be elevated in practitioners who are beginning treatment on patients with hypercortisolism. Presentation: Monday, July 14, 2025