Primary central nervous system T cell lymphoma involving multiple brain and spinal cord lesions with SETD2 mutation.

Primary central nervous system lymphoma (PCNSL) is a rare extranodal lymphoma, with diffuse large B cell lymphoma accounting for most cases. T cell variants are uncommon and associated with poor outcomes. We report a case of primary CNS T cell lymphoma with simultaneous brain and spinal cord involvement. A 37-year-old Japanese man presented with impaired consciousness, and brain magnetic resonance imaging revealed multiple contrast-enhancing parenchymal lesions. Histopathological examination of a brain biopsy specimen demonstrated medium- to large-sized atypical lymphoid cells, leading to a diagnosis of peripheral T cell lymphoma, not otherwise specified (PTCL-NOS). Comprehensive systemic evaluation showed no extracranial disease; however, contrast-enhanced spinal magnetic resonance imaging revealed extensive lesions from the cervical spinal cord to the thoracic spinal cord. Next-generation sequencing analysis identified a mutation in SETD2, possibly contributing to the aggressive disease behavior. The patient received methotrexate, procarbazine, and vincristine as first-line therapy and achieved an initial radiological complete response. However, rapid disease relapse occurred with newly developed lesions in the pineal gland and cranial nerves, and the patient died shortly after initiation of consolidation therapy. This case highlights the aggressive clinical course of primary CNS T cell lymphoma with spinal cord involvement and underscores the importance of molecular genetic profiling in this rare entity.