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A pheochromocytoma (also phaeochromocytoma, English spelling) is a
tumor in the medulla of the adrenal glands (or, rarely, the ganglia of
the sympathetic nervous system) which secretes excessive amounts of
catecholamines, usually epinephrine and norepinephrine.
Symptoms and signs
Pheochromocytomae occur most often during young-adult to mid-adult
life. Less than 10% of pheochromocytomas are malignant (cancerous).
These tumors can form a pattern with other endocrine gland cancers
which is labelled multiple endocrine neoplasia. Pheochromocytoma is
listed within the groups MEN 2a and MEN 2b.
The signs and
symptoms of a pheochromocytoma are those of sympathetic nervous system
hyperactivity: elevated heart rate and blood pressure and anxiety
often resembling that of a panic attack.
One diagnostic test for a pheochromocytoma is to administer clonidine
(Catapres?), a centrally-acting alpha-2 agonist used to treat high
blood pressure. Clonidine mimics catacholamines in the brain, causing
it to reduce the activity of the sympathetic nerves controlling the
adrenal medulla. A healthy adrenal medulla will respond to clonidine
by reducing catacholamine production; the lack of a response is
evidence of pheochromocytoma. Another test is for the clinician to
press gently on the adrenal gland. A pheochromocytoma will often
release a burst of catacholamines, with the associated signs and
symptoms quickly following.
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