Bilateral optic neuritis preceding a Baló concentric sclerosis lesion: A case report and literature review.

Baló's concentric sclerosis (BCS) is a rare inflammatory demyelinating disorder characterised by a pathologic appearance of concentric layers of demyelinated and partially myelinated fibres, with a distinctive "onion bulb" pattern on magnetic resonance imaging (MRI). Due to its rarity and overlapping features with multiple sclerosis and neuromyelitis optica spectrum disorder (NMOSD), diagnosis is challenging. We report the case of a 60-year-old male with hypertension who presented with acute bilateral painless vision loss, absent pupillary light reflex, and marked photophobia. Initial brain and orbital MRI were normal, but cervical spine MRI revealed a demyelinating lesion from C5 to C6. Cerebrospinal fluid (CSF) showed type 1 oligoclonal bands and negative anti-aquaporin 4 and anti-myelin oligodendrocyte glycoprotein antibodies. The patient was initially diagnosed with seronegative NMOSD and treated with intravenous methylprednisolone without improvement. One month later, he developed spastic dysarthria and dysphagia; brain MRI showed a right pre-Rolandic lesion with concentric rings associated with the previously reported demyelinated lesion in the cervical spinal cord and other demyelinated lesions in the brainstem. CSF analysis during relapse revealed hyperproteinorrhachia and mild hypoglycorrhachia without infectious or autoimmune markers. Plasmapheresis led to the resolution of bulbar symptoms. Given clinical relapse and lesion progression, rituximab therapy was initiated, achieving clinical stability. This case illustrates the diagnostic complexity of BCS, the importance of integrating imaging and immunological findings, and the potential role of B-cell-depleting therapy in preventing new relapses.