The true incidence of severe chronic neutropenia is now known, but these are rare hematological disorders. Based on case findings in the Puget Sound area of western Washington in the US, it is estimated that there is approximately one case per 100,000 population (Dale, unpublished observations). Cyclic neutropenia is probably the rarest syndrome, with an estimated frequency of one per million. Congenital and idiopathic neutropenia are more common, with an estimated frequency of one per 200,000 population. Estimates in other regions suggest perhaps a somewhat lower incidence. Mild neutropenia is more common in certain racial and ethnic groups; it is not known if severe chronic neutropenia is more common in these populations.
Severe chronic neutropenia is most frequently encountered as a pediatric problem. Children born with severely reduced neutrophils have a great predilection for infections, due to the combination of the reduced neutrophils and immaturity of a variety of the components of the host’s defense system. Across the spectrum of these patients, clinical symptoms tend to diminish with increasing age, despite persistence of low neutrophil counts.
Congenital, cyclic and chronic idiopathic neutropenia are primarily attributed to impaired neutrophil production.