About Pheochromocytoma
Pheochromocytomas are uncommon, catecholamine-releasing tumors, with about 90% of them located in an adrenal gland. They occur in one of every 1,000 patients with hypertension. In such cells, there are high concentrations of norepinephrine and epinephrine. Most pheochromocytomas secrete primarily norepinephrine.1
Pheochromocytomas appear most frequently between age 30 and 50.2 The tumors are highly vascular, with fewer than 10% malignant. They lead to hypertension, and are treatable. If they remain untreated, they can be fatal.3
Clinical manifestations and diagnostic considerations
Hypertension is the most common manifestation. When an affected patient experiences paroxysm or hypertensive crisis, as more than half do, it may be frequent or sporadic. These episodes usually have a sudden onset and last from a few minutes to several hours or more. They are characterized by such symptoms as headache, sweating, palpitations, anxiety, and increased metabolic rate.3 There are several cardiovascular complications, the most common of which is myocarditis, a focal myocardial necrosis.1
Analysis of a single 24-hour urine sample can establish a diagnosis by demonstrating increased production of catecholamines or their metabolites. The patient must be hypertensive or symptomatic at the time of collection.3
A treatable disorder
Surgery is the mainstay of treatment for patients with pheochromocytoma. Preoperative preparation is necessary to minimize surgical morbidity and mortality rates caused by severe hemodynamic instability. Treatment generally starts with phenoxybenzamine to induce a long-lasting alpha-adrenergic blockade. The combination of Demser® (metyrosine) with the alpha-blocker has been effective in establishing better blood pressure control, less blood loss, and less need for intraoperative fluid replacement than the alpha-blocker used alone,2 Demser® is a false catecholamine precursor that inhibits the enzyme tyrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis. Demser reduces catecholamine synthesis by up to 80%.1
Important Safety Information
DEMSER® (Metyrosine) inhibits tyrosine hydroxylase which catalyses the first transformation in catecholamine biosynthesis, i.e., the conversion of tyrosine to dihydroxyphenylalanine (DOPA). When DEMSER is used preoperatively, adequate intravascular volume must be maintained intraoperatively (especially after tumor removal) and postoperatively to avoid hypotension and decreased perfusion of vital organs. Life threatening arrhythmias may occur during anesthesia and surgery. DEMSER does not eliminate the danger of hypertensive crises or arrhythmias during manipulation of the tumor. DEMSER may add to the sedative effects of alcohol and other CNS depressants. Metyrosine crystalluria has been observed in a few patients. Patients should be urged to maintain water intake sufficient to achieve a daily urine volume of 2000mL or more. If crystalluria persists, the dosage should be reduced or the drug discontinued. DEMSER should be used with caution in patients with impaired hepatic or renal function, and in patients receiving phenothiazines or haloperidol. Safety of use in pregnancy has not been established and caution should be exercised when DEMSER is administered to a nursing woman. Safety and efficacy in pediatric patients under the age of 12 has not been established. The most common adverse reaction to DEMSER is moderate to severe sedation, which has been observed in almost all patients. Extrapyramidal signs such as drooling, speech difficulty and tremor have been reported in 10 percent of the patients, occasionally accompanied by trismus and frank Parkinsonism. Anxiety and psychic disturbances may occur. Diarrhea occurs in about 10 percent of patients and may be severe. Other adverse reactions have been reported.
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Reference: 1. 1. Root RK. Pheochromocytoma – recent advances in diagnosis and treatment. West J Med. 1988; 148:561-67. 2. Perry RR, Keiser HR, Norton JA et al. Surgical management of pheochromocytoma with the use of metyrosine. Ann Surg. 1990; 621-28. 3. Landsberg L, Young JB. Pheochromocytoma. In: Kasper DL, Fauci AS, Longo DL, eds. Harrison’s Principles of Internal Medicine. New York. 16th ed. McGraw-Hill. 2005; 2148-2150.
