Inflammatory Optic Neuritis: From Multiple Sclerosis to Neuromyelitis Optica

Inflammatory optic neuritis represents a frequent clinical situation in neurology and ophthalmology. In those parts of the world where multiple sclerosis is common, it is the condition most discussed as the cause of optic neuritis. However, the risk for conversion from optic neuritis to multiple sclerosis is evaluated at only around 50% after 15 years of follow-up. The risk is higher in cases in whom abnormalities typical of multiple sclerosis are found on magnetic resonance imaging of the brain and oligoclonal bands found on cerebrospinal fluid protein electrophoresis with no corresponding bands in serum. When these investigations are normal, optic neuritis is usually considered as "idiopathic" with a suspected viral aetiology, but in some cases, a systemic disease such as sarcoidosis, systemic lupus erythematosis, or Sjögren syndrome may be diagnosed. In rare cases, either recurrent optic neuritis or myelitis may occur without any evidence for multiple sclerosis. In the first case, it corresponds to a recently characterised disorder referred to as chronic relapsing inflammatory optic neuropathy and in the second case to a recently better identified entity, neuromyelitis optica. In the present paper, the differential diagnosis of inflammatory optic neuritis is presented from multiple sclerosis to infectious optic neuritis, systemic disease, and neuromyelitis optica.