Occult ACTH-secreting pheochromocytoma
Martina De Martin, Francesca Pecori Giraldi, Luca Pagliardini, Francesca Cassarino, Alberto G Ambrogio & Francesco Cavagnini
A 69-year-old woman developed hypertension, polyuria and hyperglycemia over the course of several months. The initial biochemical investigation revealed ACTH-dependent hypercortisolism (UFC 409.7 μg/24 h, NR 1080; ACTH 43.3 pg/ml, NR 850; OST 28 μg/dl) and moderately elevated urinary catecholamines (E 80.5 μg/24 h, NR 2.533.6; norE 235.8 μg/24 h, NR 18.1128.2). Further investigations disclosed absent ACTH and cortisol responses to CRH and a paradoxical cortisol increase after 8 mg dexamethasone (from 19.5 to 42.3 μg/dl). Imaging studies were inconclusive as pituitary MR showed only slight pituitary stalk deviation and abdominal and thoracic CT failed to identify mass lesions except for enlargement of the left adrenal gland. Indeed, increased uptake by the left adrenal gland was shown by FDG-PET. Plasma catecholamines proved to be very high (E 835 ng/l NR 10196; norE 2789 ng/l NR 78521) and did not suppress after clonidine (1076 and 3525 ng/l, respectively). However, MIBG scintigraphy was negative and MR failed to visualize an adrenal or extraadrenal pheochromocytoma. She was then submitted to PET/CT scanning with F18-DOPA, an alternative tracer for chromaffin tissue, which visualized abnormal uptake between the middle third of left kidney and pancreatic tail. Re-evaluation of imaging allowed the identification of a previously misclassified pararenal mass. The lesion was removed and pathology revealed a pheochromocytoma. The tumoral specimen also produced ACTH and synthesized POMC, as assessed by RT-PCR. After surgery, urinary catecholamines levels fell abruptly (E 1.4 μg/24 h and norE 11.6 μg/24 h) as did UFC (11.9 μg/24 h). ACTH and cortisol responses to CRH normalized (from 29.3 to 52.3 pg/ml for ACTH and from 8 to 11 μg/dl for cortisol) as did cortisol suppression after 1 mg dexamethasone (1.5 μg/dl). Hypertension and diabetes disappeared and the patient is doing well without steroid replacement therapy.
Conclusion: This case illustrates the complexities in visualizing the source of certain endocrine disorders. In the present case, localization of the pheochromocytoma, who secreted ACTH as well as catecholamines, proved particularly difficult.