MYELODYSPLASTIC
SYNDROMES (MDS)
The
MDSs are a group of disorders of the myeloid stem cell that cause dysplasia (abnormal development) in one
or more types of cell lines. The most common feature of MDS—dysplasia of the
RBCs—is manifested as a macrocytic anemia; however, the WBCs (myeloid cells,
particularly neutrophils) and platelets can also be affected. Although the bone
marrow is actually hypercel-lular, many of the cells within it die before being
released into the circulation. Therefore, the number of affected cells in the
circula-tion is typically lower than normal. In addition to the quantitative
defect (ie, fewer cells than normal), there is also a qualitative de-fect: the
cells are not as functional as normal. The neutrophils have diminished ability
to destroy bacteria by phagocytosis; platelets are less able to aggregate and
are less adhesive than usual. The result of these qualitative defects is an
increased risk for infection and bleeding, even when the actual number of
circulating cells may not be excessively low. A significant proportion of MDS
cases evolve into acute myeloid leukemia (AML); this type of leukemia tends to
be nonresponsive to standard therapy.
Primary
MDS tends to be a disease of the elderly; more than 80% of patients with MDS
are older than 60 years of age. Sec-ondary MDS may occur at any age and results
from prior toxic exposure to chemicals, including chemotherapeutic medications
(particularly alkylating agents). Secondary MDS tends to have a poorer
prognosis than does primary MDS.
The
manifestations of MDS can vary widely. Many patients are asymptomatic, with the
illness being discovered incidentally when a CBC is performed for other
purposes. Other patients have profound symptoms and complications from the
illness. Fa-tigue is often present, at varying levels. Neutrophil dysfunction
renders the person at risk for infection; recurrent pneumonias are not
uncommon. Because platelet function can also be altered, bleeding can occur.
These problems may persist in a fairly steady state for months, even years.
They may also progress over time; as the dysplasia evolves into a leukemic
state, the complications increase in severity.
The
CBC typically reveals a macrocytic anemia; WBC and platelet counts may be
diminished as well. Serum erythropoietin levels may be inappropriately low, as
is the reticulocyte count. As the disease evolves into AML, more immature blast
cells are noted on the CBC.
With
the exception of allogeneic bone marrow transplantation (BMT), there is no
known cure for MDS. Chemotherapy has been used, particularly in patients with
more aggressive forms of the illness, typically with disappointing results
(Deeg & Applebaum, 2000; Beran, 2000). However, patients with mild
cytopenias (low blood counts) actually require no therapy. For most patients
with MDS, transfusions of RBCs are required to control the anemia and its
symptoms. These patients can develop signif-icant problems with iron overload
from the repeated transfusions; this problem can be diminished with prompt
initiation of chela-tion therapy to remove the excess iron (see Nursing
Management). In some patients, the use of erythropoietin can be successful in
reducing the need for transfusions and their attendant complica-tions. Some
patients may also require ongoing platelet transfusions to prevent significant
bleeding. Infections need to be managed aggressively and promptly.
Administration of growth factors, par-ticularly granulocyte colony-stimulating
factor (G-CSF), eryth-ropoietin, or both, has been successful in increasing
neutrophils and diminishing anemia in certain patients; however, these agents
are expensive and the effect is lost if the medications are stopped. Because
MDS tend to occur in elderly people, other chronic con-ditions may limit
treatment options. Secondary MDS and MDS that evolves into AML tend to be much
more refractory to con-ventional therapy for leukemia.
Caring
for patients with MDS can be challenging because the ill-ness is unpredictable.
As with other hematologic conditions, some patients (especially those with no
symptoms) have difficulty per-ceiving that they have a serious illness that can
place them at risk for life-threatening complications. At the other extreme,
many pa-tients have tremendous difficulty coping with the uncertain trajec-tory
of the illness and fear that the illness will evolve into AML at a time when
they are feeling very well physically.
Patients
with MDS need extensive instruction about infection risk, measures to avoid it,
signs and symptoms of developing in-fection, and appropriate actions to
initiate should such symptoms occur. Instruction should also be given regarding
the risk for bleeding. Patients with MDS who are hospitalized may require
neutropenic precautions.
Laboratory
values need to be monitored closely to anticipate the need for transfusion and
to determine response to treatment with growth factors. Patients with chronic
transfusion require-ments usually benefit from a vascular access device for
this pur-pose. Patients receiving growth factors or chelation therapy must be
educated about these medications, their side effects, and ad-ministration
techniques.
Chelation
therapy is a process that is used to remove excess iron acquired from chronic
transfusions. Iron is bound to a sub-stance, the chelating agent, and then
excreted in the urine. Oral forms of chelating agents have not been successful
(due to either diminished efficacy or excessive toxicity). Chelation therapy is
most effective as a subcutaneous infusion administered over 8 to 12 hours; most
patients prefer to do this at night. Because chela-tion therapy removes only a
small amount of iron with each treat-ment, patients with chronic transfusion
requirements (and iron overload) need to continue chelation therapy as long as
the iron overload exists, potentially for the rest of their lives. Patients who
are embarking on chelation therapy must be highly motivated and need
instruction in the subcutaneous infusion technique, in-fusion pump maintenance,
and side effect management. Local erythema at the injection site is the most
common reaction and typically requires no intervention. Patients should have
baseline and annual auditory and eye examinations, because hearing loss and
visual changes can occur with treatment.
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