Neuromyelitis Optica

Neuromyelitis Optica (NMO) is a rare relapsing autoimmune disorder that preferentially causes inflammation in the optic nerve and spinal cord.  It is characterized by longitudinally extensive transverse myelitis (LETM, myelitis which is 3 vertebral segments in length or greater), which can leave one quite debilitated at presentation, and unilateral or bilateral optic neuritis.  It was once thought of as a variant of Multiple Sclerosis (MS), and is still oftentimes misdiagnosed as MS.  However, several factors differentiate it from MS: 1) it does not often involve the brain, especially early in the disease, 2) the severity of attacks is more robust as compared to MS, and 3) the pathophysiology differs from MS – whereas MS is thought to largely be a T-cell mediated disease, NMO is mediated by anti-aquaporin 4 antibodies.  Blood testing includes an anti-aquaporin-4 antibody (NMO-IgG) test, which is highly specific (>99%) and its sensitivity ranges from 48-72%, depending on the assay used. Treatment for this disease involves acute management with therapies, including IV methylprednisolone and plasma exchange (PLEX), and prevention of future attacks with immunosuppressants, including mycophenolate mofetil or rituximab, and aggressive rehabilitation.

EPIDEMIOLOGY

NMO can affect children as young as 3 years and adults as old as 90 years. While MS is more prevalent among Caucasians, NMO disproportionately affects those of African descent.  It is more common in women, particularly the relapsing form of NMO. Seventy percent of NMO patients have relapses after their initial symptoms.  The onset of NMO varies from childhood to adulthood, and the age of onset is about 40.  In a more recent study published by Mealy et al, of the cohort of 187 patients from three academic centers in the United States, there were 14 patients with onset as a minor, with only 5-8 being pre-menses in their development.  Children are more likely to be NMO IgG seronegative. Typically, the average age of onset is about 10 years later than that of MS.