I-123 MIBG imaging of pheochromocytoma-paraganglioma syndrome with succinate dehydrogenase deficiency

Learning Objectives Succinate dehydrogenase deficiency (type B) is associated with Pheochromocytoma-Paraganglioma syndrome, which can result in wide metastatic extra-adrenal paragangliomas. Whole-body I-123 MIBG or I-131 MIBG scintigraphy was the first imaging used for the diagnosis and follow-up of catecholamine-secreting tumors, and is very useful in the detection of Pheochromocytoma-Paraganglioma syndrome.

Pheocromocytoma-Paraganglioma syndromes are associated with mutations in 3 different genes that encode subunits B, C, and D of the mitochondrial enzyme succinate dehydrogenase (SDH), which catalyzes the oxidation of succinate to fumarate in the Krebs cycle [1-2]. SDH mutation caused enzymatic activity change in the mitochondrial electron transport chain can activate a hypoxic-angiogenic pathway with an accumulation of succinate and the transcription of a number of genes involved in tumorigenesis, angiogenesis, and resistance to apoptosis [1-2]. Succinate dehydrogenase deficiency contributes to the predisposition to metastatic paragangliomas. Here we present a case of a 35 year-old man with abdominal pain, hypertension and several episodes of tachycardia, with markedly elevated plasma normetanephrine levels. CT images showed a large heterogeneous retroperitoneal mass. Surgical resection and Pathological report reveled paraganglioma. Anterior and posterior views of I-123 MIBG imaging demonstrate numerous foci of I-123 uptake in the skull base, C3 spine, right shoulder, left shoulder, right posterior lateral rib, left proximal femur and acetabulum, sacrum, left iliac bone, mid-thoracic spine, the right retroperitoneum, liver, chest, etc, consistent with extra adrenal paragangliomas. The patient was identified with succinate dehydrogenase deficiency (type B), which is associated with Pheochromocytoma-Paraganglioma syndrome, Type 4, and can result in extra-adrenal paragangliomas which tend to metastasize widely.