Primary progressive multiple sclerosis to be treated with ocrelizumab: a mistaken case of cobalamin deficiency.

Cobalamin (vitamin B12) deficiency often manifests with neurologic symptoms and may rarely mimic multiple sclerosis (MS) among other neurological disorders. However, MRI changes associated with cobalamin deficiency are typically spinal predominant and distinct from MS-related changes. We report a case of a patient with cobalamin deficiency who was recommended by her primary neurologist to commence treatment with ocrelizumab, a potent anti-CD20 B-cell depleting monoclonal antibody, after being diagnosed with primary progressive MS. However, cervical spine MRI demonstrated changes classical of cobalamin deficiency including 'inverted V sign' signal hyperintensity and following parenteral cobalamin supplementation her neurological symptoms quickly and dramatically improved.