A 53-year-old man presented with a 1-week history of headaches, new-onset insomnia, anxiety and fevers but without other neurological or systemic symptoms. There was no infectious prodrome or medical history of note. Initial neurological examination, including funduscopy, was normal. Cerebrospinal fluid (CSF) analysis showed normal glucose of 2.7 mmol/L, with elevated protein at 1.33 g/L. There were 798 leucocytes, with 776 monocytes and 22 polymorphs. Extensive infectious studies were negative, including PCR and culture of viral, bacterial and mycobacterial organisms. Fevers resolved quickly, though headaches continued for some weeks. Repeat CSF was done on several occasions. Opening pressure was always normal, as was glucose. There was a persistently elevated protein and a reducing mononuclear-predominant pleocytosis. Extensive antibody tests, including anti-NMDA and AQP4, were all negative. CSF oligoclonal bands were positive. Metagenomic next generation sequencing testing for infectious organisms (at UCSF) was negative. Imaging of the brain and spinal cord with contrast on several occasions was unremarkable, though with questionable perivascular radial enhancement. There was no leptomeningeal enhancement (). Flow cytometry, however, showed a persistent small monoclonal B cell population (0.3% of lymphocytes), expressing CD19, CD20 and kappa light chains, though the most recent CSF analysis did not show this and cytology was always normal. Peripheral blood flow cytometry, moreover, was normal. CT imaging of the body was normal. Bone marrow biopsy was not performed. This was thought not to be significant given low number and resolution. The patient’s headaches resolved, although there was some persistent insomnia. An examination 1 month later showed asymptomatic optic disc swelling and haemorrhages. CSF pressure at this time remained normal, as was repeat imaging of the brain and orbits. For this reason, anti-MOG (flow cytometry live cell-based assay, Children’s Hospital Westmead, Sydney, Australia) and anti-GFAP antibodies (alpha cell-based assay, Mayo Clinic) were tested and found to be positive in CSF. They were not tested in serum. The titre was not available. The patient had made a full recovery, with resolution of papillitis, and therefore no immunotherapy was commenced. He remains well 5 months later.