Neuromyelitis Optica

Neuromyelitis Optica is an autoimmune disease of the central nervous system characterized by selective inflammation of the optic nerves and spinal cord. The primary pathogenic mechanism involves autoimmunity against aquaporin-4 (AQP4), an astrocytic water channel protein. AQP4-IgG autoantibodies bind to AQP4 on astrocyte foot processes, triggering complement-mediated destruction of astrocytes and oligodendrocytes, leading to demyelination and axonal loss. This explains the selective involvement of astrocyte-rich tissues (gray matter of spinal cord, optic nerve head). About 80% of NMO patients are AQP4-IgG seropositive; 10% have anti-myelin oligodendrocyte glycoprotein (MOG) antibodies; and 10% are seronegative. NMO attacks involve inflammation of optic nerves causing acute vision loss and eye pain, and inflammation of spinal cord causing acute motor, sensory, and autonomic symptoms. Unlike multiple sclerosis which shows gradual progressive disability, NMO causes disability primarily through recurrent attacks with incomplete recovery. Recurrent attacks progressively damage neural tissue, leading to cumulative disability. The disease can be monophasic with a single attack or relapsing with multiple attacks. Early recognition and initiation of immunosuppression is critical to prevent relapse and reduce disability accumulation. Long-term immunosuppression or anti-complement therapies aim to prevent relapses.