Encyclopedia of Health and Medicine

152 The Blood and Lymph
See also B-CELL LYMPHOCYTE; CELL STRUCTURE AND
FUNCTION; GRANULOCYTE; HEMATOPOIESIS; LYMPHOMA;
MONOCYTE; MULTIPLE MYELOMA; NATURAL KILLER (NK)
CELL; THYMECTOMY.
lymphocytopenia A decline in the number of
lymphocytes in the BLOOD to fewer than 1,000
lymphocytes per microliter of whole blood. Lymphocytes
circulate in the blood and the LYMPH,
their primary role being to identify and attack
invading pathogens to prevent and fight INFECTION.
Lymphocytopenia often accompanies IMMUNODEFI-
CIENCY disorders, notably HIV/AIDS (in which it may
be one of the earliest indications of infection),
infections such as TUBERCULOSIS and HEPATIS, and
AUTOIMMUNE DISORDERS such as SYSTEMIC LUPUS ERY-
THEMATOSUS (SLE) and MYASTHENIA GRAVIS. Other
causes include RADIATION THERAPY as cancer treatment,
long-term PUVA (psoralen plus ultraviolet
light of A wavelength) PHOTOTHERAPY for treatment
of PSORIASIS, severe stress, and medications such
as CORTICOSTEROID MEDICATIONS. Lymphocytopenia
may be transitory, with the LYMPHOCYTE level
returning to normal when the underlying cause
improves. Depending on the cause, people who
have lymphocytopenia may show few symptoms.
Treatment targets the underlying condition.
The health consequences of lymphocytopenia
vary with the overall status of the IMMUNE SYSTEM.
See also LEUKOPENIA; NEUTROPENIA; THROMBOCY-
TOPENIA.
lymphoma A type of CANCER that affects the
hematopoietic functions of the LYMPH system that
results in the uncontrolled proliferation of lymphocytes,
the type of LEUKOCYTE (white BLOOD cell)
that the lymph tissues primarily produce. The
lymphocytes congregate in the lymph tissues to
form tumors.
LYMPHOMA VS. LEUKEMIA
LEUKEMIA and LYMPHOMA are both cancers that can
affect the lymphocytes. However, leukemia is a
CANCER of the BONE MARROW that alters the development
and proliferation of lymphocytes that
enter the BLOOD circulation. Lymphoma is a cancer
of the lymphatic tissues that produce lymphocytes.
Though there are nearly three dozen identified
types of lymphoma doctors assign them to one of
two major categories, Hodgkin’s lymphoma and
non-Hodgkin’s lymphoma. Doctors diagnose about
60,000 people with lymphoma in the United States
each year. Lymphoma is the fifth most common
kind of cancer among American adults and the
third most common kind of cancer among children.
How Lymphoma Develops
Lymphomas originate in the reticuloendothelial or
clone cells in the lymph structures that produce
lymphocytes, notably the lymph nodes and the
SPLEEN. Most lymphomas affect B-cell lymphocytes
(B-cells) though some affect T-cell lymphocytes
(T-cells). Hodgkin’s lymphoma involves a specific
kind of B-cell called a Reed-Sternberg cell. In all
lymphomas, the affected lymphocytes proliferate
and migrate to lymph tissues, such as lymph
nodes and the spleen. The lymphocytes cluster
into tumorous formations that drain the NUTRIENTS
and other resources healthy cells require, causing
the healthy cells to die and allowing the cancerous
lymphocytes to continue proliferating.
A key marker for the extent and severity of
lymphoma is whether tumors are present on only
one side or on both sides of the DIAPHRAGM. Lymphomas
present only on one side of the
diaphragm (either above or below) tend to be less
aggressive than those that are present in LYMPH
NODE regions on both sides of the diaphragm, as
well as more responsive to treatment (particularly
those above the diaphragm). Cancerous lymphocytes
can also metastasize to other kinds of tissues
throughout the body, primarily traveling through
the lymphatic system. The most common sites for
lymphoma METASTASIS outside the lymphatic system
are the BRAIN, SKIN, BONE, and BONE MARROW.
However, because the lymphatic network extends
throughout the interstitial tissues, metastases in
advanced disease can appear anywhere.
Hodgkin’s Lymphoma
Hodgkin’s lymphoma, also called Hodgkin’s disease,
accounts for about 15 percent of diagnosed
lymphomas. It most commonly affects people
between ages 16 to 34 and over age 55. The presence
of specifically abnormal B-cells, Reed-Sternberg
cells, is the hallmark of Hodgkin’s lymphoma.