To highlight an unusual clinical phenotype in a patient with Myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), negative for MOG-IgG in serum but positive in CSF.

MOGAD) is a distinct autoimmune demyelinating disease. Diagnosis relies on a core demyelinating event , MOG-IgG positivity and exclusion of a better explanation. Multiple cranial neuropathies are rare in MOGAD (1-5%). Serum is optimal for MOG-IgG testing but isolated CSF MOG-IgG cases are reported.

Case report

A 28-year-old man with hypertension presented with a one-week history of bilateral vision loss, occipital headaches, and ataxia. Examination revealed severe bilateral vision loss and multidirectional nystagmus. Initial MRI of the brain, orbits, and spine were unremarkable. CSF showed lymphocytic pleocytosis (96/µL), elevated protein (175 mg/dL), positive kappa free light chains, and negative serum aquaporin-4-IgG and MOG-IgG. After three days of high-dose methylprednisolone, vision improved but relapsed upon steroid cessation. Two weeks later, he was admitted to our institution, and his neurological examination was significant for visual acuity of 20/400 OD and 20/100 OS, without optic disc edema. Repeat brain MRI revealed non-longitudinal bilateral intracanalicular optic nerve, confirming bilateral optic neuritis and cisternal trigeminal and oculomotor enhancement. Repeat lumbar puncture showed lymphocytosis (80/µL), and positive oligoclonal bands. Infectious testing, neural antibody testing, and PET/CT were negative. CSF MOG-IgG by live cell-based assay was positive at high titer (1:512[normal, <1:2]) allowing fulfillment of 2023 MOGAD diagnostic criteria (Optic neuritis, CSF MOG-IgG positive, negative aquaporin-4-IgG, and supporting features present, no alternative better explanation). The patient received high-dose steroids and plasmapheresis, and a slow prednisone taper, with a plan to consider monthly IVIg. At four weeks of follow-up, visual acuity improved to 20/40 OD and 20/25 OS. 

CSF MOG-IgG testing may be helpful in patients suspected of MOGAD who are negative for MOG-IgG in serum and may inform diagnosis and therapeutic approach.