Marked Thrombocytosis in Chronic Eosinophilic Pneumonia and Analysis of Cytokine Mechanism

A 47-year-old woman with marked thrombocytosis of 1,650 × 10(9)/L was diagnosed with chronic eosinophilic pneumonia (CEP) based on imaging of the lung and abundant eosinophils in bronchoalveolar lavage fluid. Known gene abnormalities that cause eosinophilia were not detected in bone marrow cells. Treatment with oral prednisolone at 20 mg/day relieved the CEP and resolved the laboratory abnormalities, including eosinophilia and thrombocytosis. Serum concentrations of interleukin (IL)-5 and IL-6 were elevated to 9.6 and 14.0 pg/mL, respectively. The megakaryocyte-potentiating activity of IL-6 and possibly, that of IL-1β, which is known to be secreted by activated eosinophils, may have caused the marked thrombocytosis in this patient.