Mid-gut ACTH-secreting neuroendocrine tumor unmasked with 18 F-dihydroxyphenylalanine-positron emission tomography

[摘要] Ectopic ACTH Cushing’s syndrome (EAS) is often caused by neuroendocrine tumors (NETs) of lungs, pancreas, thymus, andother less frequent locations. Localizing the source of ACTH can be challenging. A 64-year-old man presented with rapidlyprogressing fatigue, muscular weakness, and dyspnea. He was in poor condition and showed facial redness, proximalamyotrophy, and bruises. Laboratory disclosed hypokalemia, metabolic alkalosis, and markedly elevated ACTH andcortisol levels. Pituitary was normal on magnetic resonance imaging (MRI), and bilateral inferior petrosal sinus bloodsampling with corticotropin-releasing hormone stimulation showed no significant central-to-periphery gradient of ACTH.Head and neck, thoracic and abdominal computerized tomography (CT), MRI, somatostatin receptor scintigraphy (SSRS), and18F-deoxyglucose-positron emission tomography (FDG-PET) failed to identify the primary tumor. 18F-dihydroxyphenylalanine(F-DOPA)-PET/CT unveiled a 20-mm nodule in the jejunum and a metastatic lymph node. Segmental jejunum resectionshowed two adjacent NETs, measuring 2.0 and 0.5 cm with a peritoneal metastasis. The largest tumor expressed ACTH in 30%of cells. Following surgery, after a transient adrenal insufficiency, ACTH and cortisol levels returned to normal values andremain normal over a follow-up of 26 months. Small mid-gut NETs are difficult to localize on CTor MRI, and require metabolicimaging. Owing to low mitotic activity, NETs are generally poor candidates for FDG-PET, whereas SSRS shows poor sensitivityin EAS due to intrinsically low tumor concentration of type-2 somatostatin receptors (SST2) or to receptor down regulation byexcess cortisol. However, F-DOPA-PET, which is related to amine precursor uptake by NETs, has been reported to have highpositive predictive value for occult EAS despite low sensitivity, and constitutes a useful alternative to more conventionalmethods of tumor localization.

[学科分类] 血液学

[关键词] Adult;Male;White;Switzerland;Adrenal;Pituitary;Adrenal;Pituitary;Neuroendocrine tumour;Ectopic Cushing's syndrome;Hypertension;Fatigue;Myasthaenia;Dyspnoea;Muscle atrophy;Skin thinning;Hypokalaemia;Metabolic alkalosis;ACTH;Cortisol (serum);Cortisol;free (24-hour urine);Dexamethasone suppression (high dose);PET scan;CT scan;Potassium;Histopathology;Octreotide scan;Resection of tumour;Lymphadenectomy;Cortisol;Pasireotide;Oncology;Radiology/Rheumatology;Novel diagnostic procedure;March;2015