Endocrine Abstracts

Introduction

A pheochromocytoma is a tumor arising from adrenomedullary chromaffin cells that commonly produces one or more catecholamines. About 80 to 85% of chromaffin-cell tumors are pheochromocytomas. It is recommended that initial biochemical testing should include measurements of plasma free metanephrines or urinary fractionated metanephrines. ¹²³I-metaiodobenzylguanidine (MIBG) scintigraphy is a functional imaging modality, in patients with increased risk of metastatic disease.¹ Radiolabelled MIBG treatment is indicated in tumours showing adequate uptake and retention of the radionuclide and these include pheochromocytomas, paragangliomas and medullary thyroid cancer.²

Clinical case

In 2015, a 50 year-old woman, with hypertension was sent to Endocrinology practice in the setting of palpitations, headache, flushing and uncontrolled blood pressure values for 3 months, over an incidental discover (from an abdominal computed tomography – TC) of an adrenal nodule (33 × 36 × 40 mm) with extensive central necrosis suggestive of pheochromocytoma. Laboratory workup revealed normal plasma fractionated metanephrines and 24-hour urine fractionated metanephrines and catecholamines . ¹²³I-MIBG scintigraphy showed high uptake in the right adrenal gland, confirming pheochromocytoma diagnosis. The patient started α-blockade with phenoxybenzamine 10 mg bid and was submitted to right adrenalectomy. Histology was compatible with pheochromocytoma (Pass score: 3). In 2019, routine surveillance laboratory workup showed increased urinary metanephrine and normetanephrine levels: 545 mg/24H ( < 320) and 408 mg/24H (< 390), respectively. Scintigraphy revealed new foci of ¹²³I-MIBG uptake on the sternum body and on the diaphysis of the left femur, highly suggestive of metastatic disease. ⁶⁸Ga-DOTANOC-PET/CT showed metastatic lesions with high expression of somatostatin receptors in the axial skeleton: L4 and 9^th left rib, along with the lesions found with ¹³¹I-MIBG scan. The patient was proposed to ¹³¹I I-MIBG treatment (6400 MBq). Post-treatment ¹³¹I-MIBG scintigraphy still reveals uptake on the 9^th left rib and left femur diaphysis but the other lesions showed no uptake. The patient is now asymptomatic and under tight clinical and imagiological surveillance.

Conclusion

This case reveals the importance close, active surveillance of these patients. 131I-MIBG can be very effective as a treatment of malignant pheochromocytoma, with great safety profile and no significant side effects.