A rare case of systemic lupus erythematosus‐associated neuromyelitis optica spectrum disorder with cystic lesions and dual seropositivity for anti‐<scp>AQP4</scp> and anti‐<scp>MOG</scp> antibodies

Key Clinical Message In patients with SLE, concurrent NMOSD can manifest with optic neuritis and transverse myelitis. AQP‐4 antibody positivity confirms the diagnosis. Prompt treatment is critical to manage the acute symptoms and prevent relapses, as highlighted by a young patient's case with optic neuritis and extensive spinal cord lesions. Abstract Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune disorder of the central nervous system that affects the optic nerve and spinal cord. It is associated with autoantibodies against aquaporin‐4 (AQP‐4) and/or myelin oligodendrocytes glycoproteins. It is diagnosed based on clinical, radiological, and serological criteria, and treated with immunosuppressants in the acute phase. Long‐term immunosuppression is essential to prevent potential relapses. In this case report, we present the case of a 19‐year‐old female patient with systemic lupus erythematosus (SLE), who presented with blurriness and loss of vision in her left eye. Optical coherence tomography was normal, but a gadolinium‐enhanced cervico‐dorsal MRI showed multiple lesions extending from the brainstem to the C7‐T1 junction suggestive of longitudinally extensive transverse myelitis (LETM), the largest of which was a cystic lesion at the cervico‐spinal junction. A contrast injection also revealed left optic neuritis. Cerebrospinal fluid analysis showed elevated IgG and red blood cell count, but no oligoclonal bands. The patient tested positive for AQP‐4 autoantibodies, confirming the diagnosis of NMOSD. Treatment with intravenous methylprednisolone led to partial improvement, but the patient experienced a relapse with severe neurological symptoms, including tetraplegia and bladder and bowel dysfunction. This case illustrates the importance of considering NMOSD in the differential diagnosis of patients with SLE who present with optic neuritis and/or myelitis, especially when MRI findings are suggestive of LETM. Early diagnosis and adherence to treatment are crucial to prevent further relapses and deleterious sequelae.