Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune neuroinflammatory disorder of the central nervous system that very rarely may be a paraneoplastic phenomenon. We describe the case of a woman with a longitudinally extensive transverse myelitis (LETM). We identified a previously undiagnosed, follicular lymphoma and she was treated with the immunochemotherapy regime (obinutuzumab, cyclophosphamide, vincristine and prednisolone; O-CVP) for paraneoplastic NMOSD. Following two cycles, there was almost complete radiological remission of the myelitis and the patient showed some improvement in her neurological function. This case illustrates the heterogeneous aetiology that LETM may have and that O-CVP may be used as therapeutic option in patients with NMOSD driven by follicular lymphoma.