Progressive multifocal leukoencephalopathy as the initial manifestation of relapsed lymphoma: a case report.

Progressive multifocal leukoencephalopathy (PML) is a rare and often fatal demyelinating disease of the central nervous system (CNS) caused by the reactivation of the JC polyomavirus (JCPyV). While PML is a known complication of hematological malignancies, it is exceedingly rare for it to manifest as the initial neurological symptom of a relapsed lymphoma, occurring even before the start of new systemic chemotherapy. We present a case of a 22-year-old male with a history of lymphoma who presented with progressive neurological deficits. The patient's symptoms, including right-sided hemiparesis and aphasia, were initially mistaken for a CNS lymphoma relapse. Subsequent chemotherapy led to a rapid and severe clinical deterioration. Cerebrospinal fluid testing detected a high viral load of JCPyV. The patient underwent a brain biopsy, which revealed inflammatory changes consistent with the pathological changes of PML. This case highlights a critical diagnostic challenge and underscores the need for a high index of suspicion for PML in any immunocompromised patient with new-onset neurological symptoms, regardless of whether they have commenced new immunosuppressive therapy. It also serves as a poignant reminder of the potential for chemotherapy to exacerbate an underlying viral pathology.