Dopamine-secreting Pheochromocytomas: In Search of a Syndrome
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Pheochromocytomas rarely produce dopamine as the only catecholamine. Two cases are reported here, and a review of the literature was conducted. Unlike norepinephrine-and epinephrine-secreting tumors, dopamine-secreting pheochromocytomas lack a classic clinical presentation and are often asymptomatic. Urinary and serum metabolites cannot be relied on to make the diagnosis, and serum or urine dopamine levels (or both) must be measured when dealing with a potential pheochromocytoma. Dopamine-secreting tumors are less likely to enhance with metaiodobenzylguanidine (MIBG) scanning and may benefit from the use of positron emission tomography. Treatment is en bloc surgical excision; but unlike other pheochromocytomas, α-blockade is not indicated as it may lead to hypotension and cardiovascular collapse. Metyrosine is a medication that can be useful for preoperative control of symptoms from these tumors. The function of metyrosine is to block dopamine synthesis; it has no α-blocking effect. This medication is an option for controlling symptoms but should not be used routinely in these patients. The prognosis for patients with these tumors is worse than for those with an epinephrine- and norepinephrine-secreting tumor. Because of their asymptomatic nature, dopamine-secreting pheochromocytomas tend to be detected later and are more likely to be malignant at the time of diagnosis.