Cyclic neutropenia is another inherited type of neutropenia or in very rare cases it may be acquired. As the name indicates, in this disease neutrophil counts show a cyclic pattern with a typical cycle length of 21 days. These cycles vary from patient to patient. Some individuals remain neutropenic during the whole cycle while others have low neutrophil counts for only a few days and normal blood counts during the rest of the cycle. The frequency of bacterial infections depends on the length of the neutropenic period that the patient experiences. Those who have a longer neutropenic period within the cycle suffer more frequently from infections compared with patients who have only short neutropenic phases. If infections, fever or aphthous stomatitis (inflammation and ulceration of the mouth) occur frequently in approximately three week intervals, a diagnosis of cyclic neutropenia should be considered and serial differential blood counts need to be performed (at least three times per week over six weeks) to search for the cyclical pattern of blood neutrophils in this disease. Almost all patients with cyclic neutropenia have periods of severe neutropenia (ANC less than 200 per mm3 [0.200 x 109/L]) every three weeks with some symptoms almost every cycle, but significant infections (such as pneumonia or bloodstream infection) usually are infrequent. Cyclic neutropenia occurs because of fluctuating rates of cell production by the bone marrow stem cells. In contrast to other causes for neutropenia, in this condition the marrow changes during the cycle, from normal appearance to that of severe maturation arrest of neutrophil production and then back again to normal.
Other blood cells, such as platelets or red cells, can also show oscillations within a cyclical pattern. Cyclic neutropenia can occur sporadically, but there are families in which cyclic neutropenia is inherited with one parent and more than one child affected. Patients with cyclic neutropenia benefit from G-CSF treatment, usually requiring lower doses than those used for severe congenital neutropenia. They appear to be at little or no risk of developing MDS or leukemia.