"Mast Cell Disorders" 

Hematology/Oncology Clinics of North America Vol 14 No. 3 June 2000. It is written by Robert I Parker, MD

This chapter discusses three areas in which blood system abnormalities may be seen in systemic mast cell disease. These are: bone marrow, peripheral
blood, and functional abnormalities (bleeding problems).

Bone marrow changes:
In general, patients with an abnormally high number of cells in their marrow are more likely to show some kind of "proliferative" abnormality in their blood, including some immature blood cells, and some investigators believe this correlates with a poorer prognosis. In patients without this high number of cells in their marrow, the various kinds of blood cells in the
marrow usually mature normally. An increase in eosinophils spread throughout the marrow is frequently seen when the bone marrow is involved in
systemic disease.

The progression of marrow involvement in adults with SM is not known. Because many patients have been shown to have stable or possibly decreasing
marrow involvement in the face of progressive clinical disease, the clinical significance of the marrow burden of mast cells in SM is unclear. Studies of children with SM have yet to include enough children or to extend over long enough a period of time to allow any statements to be made regarding the progression of marrow disease or the prognostic significance of marrow involvement in these children.

The overall incidence of marrow involvement in SM is probably over-estimated, because many investigators require the presence of marrow disease for the diagnosis of systemic mastocytosis. Clusters of mast cells in lesions have been reported in the marrow in up to 90% of adults with SM. In reported groups of patients, almost all with SM showed either clusters of
mast cells or a diffuse increaseof mast cells in the marrow.

The typical bone marrow lesion consists of small areas of spindle-shaped mast cells in marrow that is fibrous. Usually abundant eosinophils and lymphocytes (two kinds of white blood cells) are mixed in with the mast
cells. Characteristic mast cell lesions are seen less often in bone marrow of children with SM. In the only such study to date, they were found in only 10 of 17 patients.

Other disorders in which mast cells are increased in the aspirate includes aplastic anemia and myelodysplasia.

A diagnosis of SM should not be made on marrow findings alone; diagnosis requires clinical symptoms appropriate for that diagnosis.

Peripheral blood abnormalities in SM

The most common abnormality noted in the peripheral blood in patients with SM is a mild to moderate anemia that occurs in one third to one half of
patients. Other abnormalities frequently noted in the CBC are a decrease in platelets, and an increase in eosinophils, which occur in up to 25% of patients.

Various malignant or premalignant hematologic syndromes have been identified in groups of patients with SM. The blood count may be consistent with
chronic myeloid leukemia or chronic myelomonocytic leukemia and are associated with poorer survival. A secondary acute leukemia can develop in these patients. A very few patients have been described with what seems to be primary acute mast cell leukemia.

SM has also been reported in conjunction with Hodgkin's lymphoma, Castleman's disease, multiple myeloma and other disorders. In most of these
cases, a direct connection between the hematologic disorder and SM was not demonstrated.

Bleeding disorders:
Clinically significant bleeding has been reported in some patients with SM. Mast cells contain heparin which is secreted on stimulation of the mast
cell. Consequently, high levels of heparin can collect in areas of dense mast cell accumulation.

Malabsorption of Vitamin K as a consequence of the GI manifestations of SM may also contribute to a systemic bleeding picture. A decrease in platelets
caused by an enlarged or overactive spleen and increased portal vein pressures as a consequence of liver infiltration may also contribute to GI bleeding in patients with SM. 


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