MICROMEGAKARYOCYTOSIS AND HEREDITARY THROMBOCYTOPENIA

Abstract

Two sibs (BS and RS) and a first cousin (BT) have been followed for several years for easy bruising, epistaxis, and low platelet counts (BS and RS 12-30,000, BT 30-60,000). BT has an unaffected sibling. Chronic Idiopathic Thrombocytopenic Purpura (ITP) was suspected but the number of raegakaryocytes (megas) seemed decreased. Splenectomy in BT led to a transient rise in platelets (max 90,000) before falling to, and remaining at, pre-operatlve levels. Pre-existing (BS, RS, and 4 normal children) and fresh (BT) marrow samples were Feulgen stained and examined for number, size, ploidy, and maturation (N=300 cells). With Feulgen staining, mega numbers were increased (2x) compared to controls. The mean mega diameter in all three patients was decreased (19 μm vs 26 μ m control). Also, the patients' megas were lower in ploidy.Maturation appeared retarded (Feulgen) but seemed to have an approximate normal distribution with Wright stain. Since mega size is related to levels of ploidy and maturation, the defect in these patients may be due to inadequate ploidization. Actual mega numbers may be increased though micromegakaryocytes may be missed on routine bone marrow smear. This family represents a form of thrombocytopenia that could be confused with chronic ITP and which will probably not respond to splenectomy.