[A case of undiagnosed pheochromocytoma caused by negative metoclopramide test]

Metoclopramide (MCP), a dopamine antagonist, was recently used as the pharmacological test for the diagnosis of pheochromocytoma. There have been no reports involving false negative cases in the MCP test. We experienced a rare case of pheochromocytoma which showed a negative MCP test, and it caused a failure of the diagnosis. A 51-year-old man visited our hospital with a sudden onset of headache and palpitation. Blood pressure was 218/98 mmHg at another hospital. When he came to our hospital, blood pressure returned to normal (120/80 mmHg), and both serum adrenaline (E) and noradrenaline (NE) were within normal limits. A computed tomography, magnetic resonance imaging, and angiography demonstrated a 1.8 x 1.8 cm right adrenal mass. No changes in blood pressure and plasma catecholamine were observed following the injection of 10 mg of MCP. The pathologically resected right adrenal gland contained a typical pheochromocytoma which was 1.0 x 1.0 cm in size and weighed 8 g. The detailed mechanism of the negative MCP test in this case was not known but might be related to the small size of the tumor.