Observational Cohort Study of Chronic Viral Infection in the Central Nervous System

Inclusion Criteria: 1. Age \> 14 years old. 2. Confirmed diagnosis of chronic viral infection of the central nervous system (CNS). 3. Signed informed consent. The diagnosis of Progressive Multifocal Leukoencephalopathy (PML) shall meet one of the following criteria:(1) Neuropathological diagnosis: Pathological examination of brain tissue shows demyelination, bizarre astrocytes, and enlarged oligodendroglial nuclei; immunohistochemical detection of JC virus (JCV) antigen.(2) Clinical + imaging + cerebrospinal fluid (CSF) diagnosis: Clinical manifestations of progressive neurological dysfunction; neuroimaging shows single or multiple asymmetric white matter lesions with large volume, mostly involving the U-fibers, and rare mass effect; detection of JC virus DNA in cerebrospinal fluid. Specific reference shall be made to the 2013 American Academy of Neurology (AAN) diagnostic criteria. For the diagnosis of other chronic viral infections of the central nervous system, the clinical manifestations shall be consistent with the characteristics of the relevant diseases, and the relevant viral DNA shall be detected in the cerebrospinal fluid. The diagnosis of all cases must be independently confirmed by two physicians from the Encephalitis Professional Group, Department of Neurology, Peking Union Medical College Hospital, with consistent diagnostic results, to be included in the study. For cases with inconsistent diagnoses, the two physicians shall conduct consultations to reach a consensus. Patients with unreached diagnostic consensus shall not be included in the study. Exclusion Criteria: 1. Presence of lumbar puncture contraindications, making it impossible to collect cerebrospinal fluid. 2. The attending physician and the researcher consider that the detection of virus in cerebrospinal fluid cannot explain the patient's clinical manifestations. 3. Inability to complete 1-year follow-up.