[Progressive multifocal leukoencephalopathy developed 3 years after related HLA-haploidentical peripheral blood stem cell transplantation].

The patient was a 22-year-old man. 8 years ago, he developed T-cell lymphoblastic lymphoma and relapsed during treatment. He underwent HLA-haploidentical peripheral blood stem cell transplantation (PBSCT) from a related donor and achieved remission. After transplantation, he developed severe chronic graft-versus-host disease (GVHD) with systemic involvement, requiring long-term administration of several immunosuppressive drugs. About 3 years and 9 months after the transplant, he was experiencing depression, anorexia, and weight loss. Brain MRI showed hyperintense lesions in T2-weighted imaging extending from the right cerebellar hemisphere to the middle cerebellar peduncle with slight enhancement, and lymphoma recurrence was also suspected. Finally, a quantitative real-time PCR test was positive for JC virus (JCV) in the cerebrospinal fluid (CSF) at 61 copies/ml, leading to a diagnosis of progressive multifocal leukoencephalopathy (PML). We considered the patient to have prolonged secondary immunodeficiency after transplantation, and gradually reduced his immunosuppressive drugs. After that, the JCV in CSF became less sensitive to detection. This case highlights the importance of monitoring for PML as a potential late complication after hematopoietic stem cell transplantation, and provides the valuable insight that improvement was achieved only through dose reduction and discontinuation of immunosuppressive drugs.