Bone marrow granulocyte reserve in chronic benign idiopathic neutropenia

Fifteen patients with chronic benign idiopathic neutropenia (CBIN) with neutrophil counts less than 1.0 X 10(9)/1 have been studied. The mean age was 33 years (range 23-50) comprising 11 females and 4 males. Bone marrow cellularity was normal except in two patients who showed slight reduction and one who had a slight increase. Bone marrow differential counts were normal apart from a small increase in the percentage of promyelocytes and reduction in the myeloid/erythroid ratio in some patients. Peripheral blood counts showed no 'compensatory' monocytosis. Epinephrine stimulation tests showed no evidence of excess neutrophil margination. After endotoxin administration there was a one- to two-fold increase in neutrophil counts in three patients, a three-fold increase in three patients and a greater than four-fold increase in the remaining nine patients. The findings suggest that the benign course of CBIN is not due to excess neutrophil margination nor to compensatory monocytosis, but that at least one mechanism includes a functionally adequate release of neutrophils to the peripheral blood under conditions of stress with subnormal delivery of neutrophils under basal conditions. The variability in responses to endotoxin suggests that CBIN is not entirely homogeneous with respect to mechanism. The findings of relatively normal bone marrow cellularity and differential counts and a normal or substantial neutrophil response to endotoxin appear characteristic. They may help predict a benign clinical course in neutropenic patients and assist diagnosis of the CBIN variant of idiopathic neutropenia.