Intravascular large B-cell lymphoma mimicking seronegative neuromyelitis optica spectrum disorder.

Intravascular large B-cell lymphoma (IVLBCL) is a rare aggressive extra-nodal lymphoma characterised by malignant B-cells proliferating within small to medium blood vessels. Often termed the 'great mimicker', it can affect almost any organ with heterogeneous clinical features. Up to half of cases have central nervous system involvement, resembling inflammatory, autoimmune or vascular disease. We report a man in his 60s presenting with saddle paraesthesia, faecal incontinence and bilateral foot drop. MR scan of the spine showed longitudinally extensive transverse myelitis, multifocal supratentorial white matter lesions and optic neuritis. He was initially diagnosed with seronegative neuromyelitis optica spectrum disorder (NMOSD), which appeared to respond well to corticosteroids, plasma exchange and rituximab. However, 8 months, later he relapsed with progressive cytopenias, a rising serum lactate dehydrogenase and new cerebral infarcts despite intensified immunosuppression. Random skin biopsies diagnosed IVLBCL. This case shows that IVLBCL can mimic seronegative NMOSD and immunosuppression may mask the true diagnosis.