Pathophysiologic mechanisms, clinical features and treatment of idiopathic neutropenia.

The term idiopathic neutropenia describes a benign disorder of granulopoiesis characterized by the unexplained reduction in the absolute neutrophil count below the lower limit of the normal range for a prolonged period. Recent studies have provided evidence that this neutropenic condition comprises two distinct disease entities on the basis of the underlying pathogenetic mechanisms: first, the primary autoimmune neutropenia mediated by autoantibodies against mature neutrophils and/or their bone marrow progenitor/precursor cells; and second, the previously named chronic idiopathic neutropenia, that might now be called chronic immunologic neutropenia, characterized by T-cell- and cytokine-mediated suppression of granulopoiesis. Despite the differences in the bone marrow granulocytic progenitor cell reserves that actually reflect the differences in the implicated pathophysiologic mechanisms, both disease entities usually display an uncomplicated clinical course with minimal symptoms. Treatment decisions should be individualized on the basis of patients' clinical course and the indicated therapies are analyzed in this review. The clinical and laboratory data characterizing these neutropenic conditions and the available in vitro data that have led to remarkable progress in the understanding of the pathophysiology of both disorders are also summarized.