Summary

Myelofibrosis, either primary or resulting from essential thrombocythemia or polycythemia vera, may present with highly variable white blood cell counts, including progressive leukopaenia with its associated risk of infections. Medications have been developed to reduce splenomegaly and other symptoms, but there are no reports of improved white blood cell counts. We report a case of primary myelofibrosis with marked improvement in leukopaenia and reduced recurrent infections, in addition to reduction in spleen size and improvement in disease-associated symptoms, within 20 weeks after using low-dose ruxolitinib. Although reduction of splenomegaly in myelofibrosis patients is the anticipated benefit of ruxolitinib, the drug may also have the potential to improve leukopaenia if used at a low dose.