Complete remission of pure white cell aplasia associated with thymoma after thymectomy and cyclosporine administration

We present the case of a 63-year-old male with pure white cell aplasia (PWCA), a rare complication of thymoma, who was successfully treated with cyclosporine A (CyA) and thymectomy. The patient presented with high fever and agranulocytosis. Complete blood count revealed a white blood cell count of 0.9 × 10⁹/L (3% neutrophils), a hemoglobin level of 15.8 g/dL, and a platelet count of 308 × 10⁹/L. Bone marrow (BM) aspiration revealed a hypocellular marrow lacking granulocytes. Computed tomography showed a large anterior mediastinal mass, and the patient was diagnosed with PWCA associated with thymoma. Thirteen days after the initiation of CyA treatment, myeloid cells appeared in the BM, and the neutrophil count in peripheral blood started to increase on day 18. Thymectomy was performed 3 months later. Although CyA treatment was discontinued after thymectomy, complete remission has been maintained for over 4 years. In vitro colony-forming unit granulocyte–macrophage (CFU-GM) assay using the patient’s serum showed severe suppression of CFU-GM colonies in the presence of the patient’s serum, suggesting the presence of CFU-GM inhibitor in the patient’s serum. The efficacy of the immunosuppressive therapy and the CFU-GM assay suggests the potential involvement of an immunological mechanism in patients with thymoma-associated PWCA.