Aplastic
AnemiaThis normocytic, normochromic anemia develops as a result of a loss
of precursor cells in the bone marrow. Among the various forms of anemias this
is quite rare. It occurs as two major forms, the more common defect of all the
cell precursors (affecting white blood cell, thrombocyte and red blood cell production);
the other less common form affects only RBC production (=erythroblastopenia).
50% of the cases are without any known causes (=idiopathic aplastic anemia), the
others are due to genetic factors (below) or secondary to a variety of causes,
chemicals (benzene, inorganic arsenic), radiation or medication (the antibiotic
chloramphenicol, non steroidal anti-inflammatories used for arthritis, anticonvulsants,
gold salts, penicillamine etc.). It is thought that some people are born with
a selective hypersensitivity of the bone marrow to some of these causes. Two
congenital forms of aplastic anemia are sometimes encountered. 1. Fanconi’s
anemia: This genetic syndrome combines aplastic anemia with bone deformities,
hypogonadism, small head size (microcephaly), 80% café-au-lait spots (skin pigmentations)
and others listed
in the link. It may go undetected until the child gets an infection
or an inflammatory condition at which time the blood tests reveal the aplastic
anemia (a combination of low white blood cells, thrombocytopenia and anemia).
When the acute precipitating condition has recovered, the blood tests normalize,
although the bone marrow still shows a reduction of the precursor cells. 2.
Diamond-Blackfan anemia: This is a congenital form of aplastic
anemia This anemia affects the red blood cell precursors in the bone marrow
and tends to occur in infancy or childhood for the first time. Short stature and
thumb abnormalities can be associated with this genetic syndrome. The diagnosis
is made by the presence of a very low or absent reticulocyte count in the blood
(immature red blood cells, stained) and an abnormal bone marrow biopsy showing
an absence of the red blood cell line. Treatment is by blood
transfusions and sometimes prednisone.
Here is a link about
general info
regarding Diamond-Blackfan anemia.
Diagnostic tests
The complete blood count in patients with aplastic anemia shows a “pancytopenia”
meaning that there is a profound absence of the granulocytes among the white blood
cells, a thrombocytopenia (platelet count far below 50,000 per micro liter), missing
red blood cells and low or missing reticulocytes. The serum iron level is high.
The bone marrow shows a lack of blood cell precursor cells of all lines except
for the pure red blood cell aplasia where the other cell lines are present and
the white blood cell and platelet counts in the blood are normal. Treatment
Treatment for aplastic anemia is by a combination of an equine anti thymocyte
globulin given as an infusion intravenously. It is based
on a trial, which showed the best survival. This infusion is given
on 10 consecutive days and combined with high corticosteroid doses starting on
day 7 to 10 and given for 10 days. About 50% of cases will respond to this; the
treatment failures are treated with cyclosporine and about 50% of these will respond
again. Combined cyclosporine and anti thymocyte globulin is effective as well.
Sometimes cytokines are used by the hematologist (erythropoietin to stimulate
RBC precursors, colony-stimulating factor to stimulate granulocyte growth etc.).
When all else fails, the final option would be a bone marrow or stem cell transplant.
The problem for this is that it has to be histocompatibility-antigen (HLA) matched.
The best tissue match is from identical twins, or from an HLA matched sibling.
Some patients have a thymus tumor that produces autoimmune antibodies. These patients
tend to get a pure RBC aplasia and respond usually well to the surgical removal
of this tumor (=thymectomy). Otherwise patients with a pure RBC aplasia of no
identifiable cause will respond to immune suppressants like cyclosporine, prednisone
or cyclophosphamide.
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