Diagnostic challenge of pheochromocytoma in a patient receiving levodopa for Parkinson's disease

The diagnosis of pheochromocytoma in patients receiving levodopa is challenging because the standard diagnostic biochemical tests may be confounded by dopaminergic therapy. We aim to showcase our experience with the diagnosis of pheochromocytoma in a patient with a known case of Parkinson's disease who was receiving levodopa. We present the case of an elderly male who was diagnosed as having pheochromocytoma while receiving dopaminergic therapy for Parkinson's disease. A 75-year-old man presented with vague abdominal symptoms. Computed tomography revealed a 3.5 x 3.2 cm right adrenal mass with a well-defined margin. As revealed by magnetic resonance imaging, the mass was hypointense on T1-weighted and hyperintense on T2-weighted images. Biochemical tests revealed elevated levels of urinary dopamine, which was considered to be caused by levodopa therapy. However, concurrent elevation in urinary adrenaline and his metanephrine and vanillylmandelic acid levels suggested an underlying case of pheochromocytoma. An 123I-metaiodobenzylguanidine (123I-MIBG) scintigraphy scan performed under levodopa therapy showed positive tracer uptake in the right adrenal gland. Histopathology of the adrenalectomy specimen confirmed the diagnosis of pheochromocytoma. Our experience with the present case indicates that although the standard diagnostic biochemical tests for pheochromocytoma may be confounded by dopaminergic therapy, 123I-MIBG scintigraphy has diagnostic value for confirming pheochromocytoma even in patients receiving dopaminergic therapy.