Familial macrothrombocytopenia with granulocyte inclusion: a clinical and laboratory problem.

The differential diagnosis of familial macrothrombocytopenia and idiopathic thrombocytopenic purpura (ITP) may be difficult owing to the similarities in their clinical and laboratory presentations, but it is important because of dissimilarities in their management and prognosis. We investigated two families with familial macrothrombocytopenia and granulocyte inclusion. The probands of both families presented with mild bleeding tendency, macrothrombocytopenia, normal bone marrow, and increased percentages of platelet-associated immunoglobulin G (IgG) and reticulated platelets. ITP had been misdiagnosed in both patients initially. Both probands failed to respond to steroid therapy. Family study revealed an autosomal dominant pattern of heredity in both families, with absence of Alport's syndrome-like features (hearing impairment, congenital cataract, and interstitial nephritis). All thrombocytopenic family members showed blue cytoplasmic inclusions in neutrophils on peripheral blood smears. Ultrastructurally, distinct granulocyte inclusions comprising clusters of rough endoplasmic reticulum, smooth endoplasmic reticulum, and polysomes were detected, without the presence of parallel filaments. The clinical, laboratory, and hereditary findings were consistent with a diagnosis of Sebastian platelet syndrome in both families. In conclusion, caution should be exercised when interpreting the percentages of platelet-associated IgG in thrombocytopenic patients, as overinterpretation may lead to misdiagnosis of macrothrombocytopenia as ITP. Family history is important, as familial ITP is rare, and careful examination of blood smears is essential.