Difficult Diagnosis and Management of Concealed Cushing.

Background: Adrenocorticotropic Hormone (ACTH)-secreting tumors account for 5- 10% of Cushing syndrome cases and are often difficult to diagnose and treat.

Case report: A 44-year-old man presented with arterial hypertension and weight gain. On the physical examination, he exhibited central obesity, abdominal striae rubrae, and facial plethora. Due to the clinical suspicion of Cushing syndrome, the Nugent test and Liddle-1 test were performed, which showed a lack of cortisol suppression. ACTH levels were also high (138 pg/mL), so pituitary MRI and dynamic tests were performed, including the Corticotropin-releasing Hormone (CRH) stimulation test and Liddle-2. MRI showed a 3 mm pituitary microadenoma, but hormonal testing suggested ectopic ACTH production. Chest CT detected a 10-mm nodule in the upper lobe of the right lung, suspicious for a carcinoid tumor. However, the nodule did not exhibit any enhancement on 68-Gallium-DOTATOC PET-CT, and further, 18-FDG PET-CT was inconclusive. In addition, the nodule was deemed non-biopsiable due to its location. Meanwhile, the patient developed osteoporosis, resulting in two vertebral fractures and one rib fracture, which was treated with zoledronate. Furthermore, the patient developed acute aortic insufficiency. During bioprosthetic valve replacement, the thoracic surgeon performed wedge resection of the right upper lung lobe. The histological examination of the lesion revealed a typical lung carcinoid (1.2x0.9 cm, pT1bNXR0, Ki671%, ACTH positive in 95% of neoplastic elements). ACTH levels dropped to 4 pg/mL on the fourth postoperative day.

Conclusion: ACTH-secreting tumors are particularly challenging diseases. A comprehensive hormonal and instrumental valuation is often required, necessitating a multidisciplinary approach.