Neuromyelitis optica spectrum disorder as a paraneoplastic syndrome: a rare and challenging diagnosis.

Neuromyelitis optica spectrum disorder (NMOSD) is an uncommon antibody-mediated disease of the central nervous system, often associated with aquaporin-4 antibodies (AQP4-Ab). NMOSD may present as a subacute myelopathy, progressing over days with MRI revealing a contiguous inflammatory lesion of the spinal cord, ≥3 vertebral segments, a longitudinally extensive transverse myelitis. We describe an unusual paraneoplastic form of AQP4-Ab NMOSD that developed in a patient with an advanced diffuse large B-cell lymphoma. The patient had an unusual hyperacute onset, reaching a clinical nadir within hours.