Hematologic aspects of mastocytosis: I: Bone marrow pathology in adult and pediatric systemic mast cell disease.

The typical bone marrow lesions seen in adults with systemic mast cell disease (SMCD) are foci of spindle-shaped mast cells in a fibrotic matrix and are found in up to 90% of adults with SMCD. Lymphocytes and eosinophils frequently are admixed with the mast cells, forming the classic MEL lesion. The mast cell lesions can be found in perivascular, peritrabecular or intertrabecular locations and may on occasion completely replace intratrabecular regions of the marrow. In contrast, the mast cell lesions found in children with cutaneous mast cell disorders are uniformly small and subtle and are most frequently located perivascularly. Lymphocytes, eosinophils, and early myeloid elements may be associated with these lesions. Of perhaps greater specificity for SMCD is the finding of confluent clusters of mast cells on the marrow aspirates; such clusters are noted in up to 30% of patients with SMCD.