polycythemia vera A myeloproliferative condi-
tion of the BLOODin which the red BONE MARROW
produces an excessive volume of erythrocytes (red
blood cells), platelets, and neutrophils that results
in increased cell volume and decreased fluid vol-
ume (PLASMA) in the blood. This myeloprolifera-
tion (overproduction by the bone marrow)
thickens the blood (hyperviscosity), making it
more difficult for the cardiovascular system to
transport and increasing the risk for thrombosis
(blood clots). As the myeloproliferation pro-
gresses, the marrow pushes immature, deformed,
and defective cells into the blood that are unable
to perform the normal functions of their cell
types. Polycythemia vera is a chronic and poten-
tially debilitating disorder most commonly diag-
nosed in people age 60 and older.
Symptoms and Diagnostic Path
Symptoms may not appear until the bone marrow
dysfunction is considerably advanced and typically
include
- tiredness and fatigue
- weakness
- HEADACHE
- lightheadedness
- easy bleeding or bruising
- PRURITUS(itching)
- SKINflushing (redness), particularly of the face
The doctor’s examination often reveals an
enlarged SPLEEN(SPLENOMEGALY), a consequence of
the overload on the spleen to remove defective
erythrocytes from the circulating blood or to pro-
duce additional erythrocytes if those in circulation
are too defective to adequately transport oxygen
(ANEMIA). Some people also have an enlarged LIVER
(HEPATOMEGALY), as the liver too has a role in
cleansing dysfunctional erythrocytes from the
blood. Diagnostic blood tests characteristically
show elevated ERYTHROCYTE, neutrophil, and
PLATELETcounts, with the hematocrit (percentage
of erythrocytes in the blood) greater than 54 per-
cent in men or 49 percent in women. The doctor
may also perform a bone marrow biopsy, which
demonstrates clusters of megakaryocytes (the par-
ent cells of platelets) and other characteristic alter-
ations in the marrow’s structure.Treatment Options and Outlook
PHLEBOTOMY(therapeutic withdrawal of blood) is
adequate treatment for many people who have
polycythemia vera, particularly when the diagno-
sis comes early in the condition. The usual thera-
peutic approach is daily phlebotomy to remove
300 to 500 milliliters of blood until the hematocrit
drops to 45 percent. Weekly to monthly phle-
botomy sessions then may keep the condition in
check.
When phlebotomy is not sufficient, substances
to suppress bone marrow function, called myelo-
suppressive therapy, can put the condition in
REMISSIONfor up to several years at a time. Myelo-
suppressive therapy has a high risk for causing
acute myeloid LEUKEMIA, however, so current
treatment protocols call for its use only in people
over age 70.
The most significant and frequent complica-
tions of polycythemia vera are thrombosis (the
formation of blood clots in the blood vessels),
which can lead to HEART ATTACKor STROKE, and
acute myeloid leukemia. Without treatment poly-
cythemia vera is generally fatal within two years.
With treatment, many people enjoy good QUALITY
OF LIFEfor 15 to 20 years beyond diagnosis.Risk Factors and Preventive Measures
Because researchers do not know what causes
polycythemia vera, there are no known preven-
tive measures. The condition is uncommon, and
more likely to occur in men than women. Poly-
cythemia vera is unusual in a person under age- Early diagnosis and treatment improves qual-
ity of life and outlook.
See also HEMOCHROMATOSIS; MYELOFIBROSIS;
THROMBOCYTHEMIA; THROMBOCYTOPENIA.
164 The Blood and Lymph