Here are the most
frequently asked questions about Pheochromocytoma, along with some
information that is important to know.
DIAGNOSIS
How is Pheochromocytoma diagnosed?
If your doctor is
suspicious of pheochromocytoma there are some standard tests that are
initially performed. The 24 hour urine tests for catecholamines,
metanephrines and VMA are fairly standard in the beginning stages of a
diagnosis. These must be performed correctly: the urine specimen must be
kept refrigerated during collection, and an acid preservative added to
the collection bottle. In some cases, unless an individual has an
episode during collection, the urine test could be negative, even with a
pheochromocytoma present. There is a blood test available which tests
Plasma Metanephrines and Catecholamines, which has been approved for
diagnosis of pheochromocytoma. This test is available through the
National Institutes of Health, and commercially through the Mayo Clinic.
Some pheochromocytoma researchers believe that because of the high
sensitivity of the plasma free metanephrines test and the low incidence
of the tumor, that plasma free metanephrines should be carried out as
the first test. If that is not available, then the next best test is
urinary fractionated metanephrines - but not urinary TOTAL
metanephrines. Both tests may be combined with measurements of plasma or
urinary catecholamines.
TREATMENT
How is Pheochromocytoma treated?
Once a diagnosis of
pheochromocytoma has been established and the tumor located, surgical
removal of the tumor is standard treatment if possible. This is not
always as simple as it sounds. Some patients with pheochromocytoma find
that it is difficult for the location of the tumor to be discovered.
There are also cases of "quiet" pheochromocytomas which take longer to
find and remove.
For pheochromocytoma surgery, it is vital to ask your surgeon how many
patients he or she has operated on specifically for this type of tumor.
An experienced surgeon will do no less than 3 to 4 pheochromocytoma
surgeries in a year.
PLASMA METANEPHRINE TEST
What makes the plasma metanephrine test different?
First, the free
metanephrines are produced continuously within pheochromocytoma tumor
cells from catecholamines leaking from storage vesicles within the cell
cytoplasm. Thus, these metabolites are produced
independently of catecholamine released by tumors. This has advantages
since catecholamine release can be episodic or relatively non-existent
in some pheochromocytomas. Second, metanephrines commonly measured in
urine are different metabolites. They are actually sulfate conjugated,
require an additional metabolic step for synthesis and are consequently
produced in different parts of the body than the free metanephrines.
Third, the advantages of a plasma test over a urine test outweigh the
disadvantages. Most urine tests have a lesser accuracy rate, whereas the
plasma metanephrine test has a much higher accuracy rate.
COMPARISON OF ACCURACY
What is the accuracy of the plasma free metanephrines test?
Testing results indicate a
sensitivity of 99% compared to 63% for VMA and 83% to 85% for urinary
or plasma
catecholamines.
INTERFERENCE WITH URINE TEST
What substances interfere with the results of 24 hour urine
tests?
Many drugs can potentially
interfere with assays of catecholamines and any other substances, but
this often depends on the method and laboratory. One facility can have
machines and equipment that vary from that being used by another
facility. Also, whether it is a problem or not depends on the level of
expertise and competency of the operator running the assay. Caffeine,
vanilla, vanilla extract, and bananas are known problems for urine
testing. Listing these interferences is best left up to the individual
laboratory responsible for the test.
INTERFERENCE WITH THE PLASMA METANEPHRINE TEST
What substances interfere with the plasma metanephrine test?
Specifically, caffeine is
a problem both directly and indirectly. Acetaminophen or any drugs
containing acetaminophen can be a problem. No other medicinal source of
interference has been identified. Clonidine or its metabolites show up
in the chromatograms but they aren't a
problem. Again, listing these interferences is best left up to the
individual laboratory responsible for the test being performed. If the
patient is not given a list of known interferences, be sure to insist on
having a copy.
NEGATIVE 24 HOUR CATECHOLAMINE URINE TEST RESULTS
What if the results are negative in the 24 hour
catecholamine urine test?
It is still recommended
that the plasma
metanephrine test be performed to confirm or eliminate the diagnosis of
pheochromocytoma, particularly if the symptoms are episodic. The 24 hour
urine tests are not always successful at picking up intermittently
secreting tumors.
SYMPTOMS
List of symptoms of Pheochromocytoma
Symptoms vary greatly with
each patient.
Sterotyped textbook cases of Pheochromocytoma are rare. Symptoms can
include:
Headaches
Nausea
Vomiting
Weight loss or gain
Hypertension
Hyperglycemia
Diabetes
Diabetes-like symptoms
Palpitations
Angina Chest Pain
Clammy skin Cold skin
Anxiety
Nervousness
Panic
Feeling of impending doom
Rapid pulse
Rapid breathing
Breathing difficulty
Vision disturbance
Impaired vision
Orthostatic hypotension
Fainting
Sweating
Flushing
Abdominal pain
Flank pain
Constipation
Paresthesia (tingling,
prickling, numbness
or burning sensations)
Lenders J.W.M., K. Pacak, M.M. Walther,
W.M. Linehan, M. Mannelli, P. Friberg, H.R. Keiser, D.S. Goldstein and
G.
Eisenhofer. Biochemical diagnosis of pheochromocytoma: Which test is
best?
Journal of the American Medical Association 287: 1427-1434,
2002.
Eisenhofer, G.; Lenders, J.W.M.; Linehan,
W.M.; Walther, M.M.; Goldstein, D.S.; Keiser, H.R. "Plasma
normetanephrine
and metanephrine for detecting pheochromocytoma in Von Hippel-Lindau
disease
and multiple endocrine neoplasia type 2." N.E.J.M. 340:24 (1999)
1872-1879.
Eisenhofer, G; Walther, W.M., et al,
"Plasma Metanephrines: Novel and Cost Effective Test for
Pheochromocytoma,"
Proceedings of the 1st International Meeting on Adrenal Diseases,
Brazilian
Journal of Medical and Biological Research, September 7, 1999.
