Monday, May 9, 2011

Pheochromocytoma and high blood pressure

Pheochromocytoma is a neuroendocrine tumor of the medulla of the adrenal glands from chromaffin cells or extra-adrenal chromaffin tissue that failed to involute after birth and secretes excessive amounts of  catecholamines, epinephrine and norepinephrine. Tumors may grow very large, but most are smaller than 10 cm.

Pheochromocytoma linked to Multiple Endocrine Neoplasia  (MEN II) can be caused by RET oncogene mutations. The symptoms and signs of a pheochromocytoma are those of sympathetic nervous system hyperactivity, The most common presentation is headache, excessive sweating, and increased heart rate, with the attack subsiding in less than one hour, the others include elevated blood pressure, elevated blood glucose level, elevated heart rate, palpitations, anxiety, headaches, pallor and weight loss.  A pheochromocytoma can be fatal if it causes malignant hypertension or severely high blood pressure.  

The diagnosis can be established by measuring catecholamines and metanephrines in plasma or through a 24-hour urine collection. Care should be taken to rule out other causes of adrenergic (adrenalin-like) excess like hypoglycemia, stress, exercise, and drugs affecting the catecholamines like methyldopa, dopamine agonist, stimulants or ganglion blocking antihypertensives. Tumors can also be located using Iodine 131 meta-iodobenzylguanidine (I131 MIBG) imaging.

Surgical resection of the tumor is the treatment of first choice, either by open laparotomy or laparoscopy. Given the complexity of  perioperative management, and the potential for catastrophic intra and postoperative complications, such surgery should be performed only at centers experienced in the area. In addition to the surgical expertise that such centers can provide, they will also have the necessary endocrine and anesthesia resources as well. It may also be necessary to carry out adrenalectomy, a complete surgical removal of the affected adrenal glands.

Either surgical option requires prior treatment with the non-specific and irreversible alpha adrenoceptor blocker Phenoxybenzamine.  The patient with pheochromocytoma is invariably volume depleted. In other words, the chronically elevated adrenergic state charactersitic of an untreated pheochromocytoma leads to near-total inhibition of rennin angiotensin activity. Volume depletion results. Hence, once the pheochromocytoma has been resected, thereby removing the major source of circulating catecholamines, a situation arises where there is both very low sympathetic activity and volume depletion. This can result in profound hypotension.    
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