AQP4 and leptomeningeal metastasis: Among them, the following patient groups had mean CSF neopterin levels higher than 23.93 pmol/mL, which was the mean + 2 standard deviations (SD) of the CSF neopterin level in the control group: the septic meningitis, aseptic meningitis, fungal meningitis, rheumatoid meningitis, encephalitis, hypertrophic pachymeningitis, AQP4-IgG-positive NMOSD, MOGAD, myelitis, HAM, HIV, neuro-Behçet’s disease, neuropsychiatric SLE, neuro-sarcoidosis, neuro-Sjögren’s syndrome, CNS lymphoma, spinal cord tumor, and meningeal carcinomatosis groups.