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Risk of Multiple Sclerosis in Optic Neuritis – Association with Neuromyelitis Optica – Optic Neuritis Symptoms, Diagnosis, Treatment, and Prognosis
Optic neuritis causes loss of vision, more commonly in one eye, due to demyelination in the optic nerve(s). Demyelination is caused by an autoimmune attack against some unknown component of the optic. The attack causes of damage to the myelin and, to some extent, to the nerve fibers. Optic neuritis is highly associated with multiple sclerosis and neuromyelitis optica.
Other reasons for optic nerve disorders, such as genetics, drug side effects, toxic chemicals, infections, strokes and cancers, are not discussed in this article. The most common causes of demyelinating optic neuritis are idiopathic optic neuritis, multiple sclerosis, and neuromyelitis optica.
Symptoms and Signs of Optic Neuritis
Typical optic neuritis causes progressive loss of vision over hours to 10 days. Deviation from this time frame points to some other cause of the disease.
Only 10% have involvement of both eyes simultaneously or over a short period of time. Involvement of both eyes is more common in children and in Asians.
Complaints of blurred vision and loss of central portion of the visual field (black spot) are the most typical. Although, almost any type of visual field defect may occur.
Another common complaint is a disproportional loss of color saturation perception (relative to visual acuity trouble). Colors look dull and washed out compared to the normal eye.
In about 11% formal testing reveals 20/20 vision. Only 3% have blindness to the point of light perception loss.
Pain in the eyeball, orbit or temple is almost universal. It is dull and achy in quality. The pain is exacerbated by eye movements.
Eye movements may bring up perception of sparkling or flickering lights.
Diagnostic Testing in Optic Neuritis
MRI of Brain and Orbits with Gadolinium
MRI allows confirmation of optic neuritis and assessment of prognosis as well as risk of multiple sclerosis in the future. Inflammation (contrast enhancement on the MRI) can be confirmed in 95% of patients with optic neuritis. Finding of brain lesions increases the chance of MS in the future.
Spinal Tap (Lumbar Puncture)
Classical cases of optic neuritis do not require a spinal tap. It is usually reserved for children, involvement of both eyes, or when infection is suspected. Elevated cell count and protein are expected. Presence of oligoclonal bands is associated with MS.
Visual Evoked Potentials (VEP)
VEP has minimal diagnostic value when obvious symptoms of optic neuritis are present. It is more useful for assessment of prior optic nerve involvement as a part of work up for multiple sclerosis.
Fundoscopy (examination of the back of the eye) is normal in two thirds of the patients. This is because the portion of the optic nerve involved is somewhat distant from the eyeball. Swollen optic disc is seen in one third of the patients. Visualization of optic nerve swelling on the examination lowers the risk of MS.
Color perception with Ishihara plates and visual fields assessments with perimetry are normally performed. Examination also reveals, so called, afferent pupillary defect. The pupil does not constrict in response to light directed to the sick eye. It does react, however, when the light beam is pointed to the other, normal, side.
Blood test for Aquaporin-4 antibodies is indicated in recurrent optic neuritis, especially with normal brain MRI. Positive test indicates a high probability of neuromyelitis optica.
Prognosis in Optic Neuritis
Vision recovery starts in a few weeks and normally continues for about 6 months. Majority of patients experience substantial vision improvement. Full recovery is not the rule, though. Even in “full” recovery there is some loss of contrast sensitivity and color depth perception on special testing.
Severe vision loss after one month and evidence of extensive optic nerve involvement on MRI are poor prognostic signs.
Severe vision loss at presentation does not always predict a poor outcome. According to ONTT study 64% of patient with severe vision loss at presentation recover to at least 20/40 or better. Whites and children have generally better prognosis.
Residual optic nerve atrophy is often seen on the eye examination in spite of even 20/20 vision. It may be explained by the fact that we need only about 50% of the nerve fiber to achieve normal vision.
Increased body temperature may lead to temporarily worsening of vision (Uhthoff’s phenomenon). It has nothing to do with recurrence of optic neuritis, but it often generates fear and anxiety.
Within 10-year period optic neuritis will recur in 35% of cases. Relapses are not side specific. Recurrent optic neuritis may involve the same, the other, or both sides. Relapse of optic neuritis increases the chance of multiple sclerosis and also requires diagnostic testing for neuromyelitis optica.
Risk of Multiple Sclerosis
After a single optic neuritis attack the risk of multiple sclerosis is 30% after 5 years and 50% at 15 years. The probability is slightly less in children. Women are twice as likely to develop MS as men.
Presence of white matter lesions on the MRI at the time of optic neuritis increases the chance of MS after 15 years threefold. Patients without lesions have 25% chance of MS. Presence of one or more lesions raises the chance to 72%.
There is no risk of MS after 10 years, when lack of brain lesions is combined with atypical features for optic neuritis, such as lack of pain, lack of light perception at presentation, or severe disc swelling.
Recurrent optic neuritis increases the chance of MS and neuromyelitis optica. Presence of AQP-4 autoantibodies in the blood is diagnostic for the latter.
Treatment of Optic Neuritis
High dose of IV Methylprednisolone for three days with or without a few days of oral Prednisone is a standard approach. It improves the speed of vision recovery and slightly decreases the chance of recurrent optic neuritis. There is no effect on the final outcome.
High dose steroids decrease the chance of MS over the 2-year period, but they do not affect the chance of MS long-term. Basically, high dose steroid treatment may only delay the first MS attack.
Patients at high risk of multiple sclerosis, based on abnormal brain MRI, statistically benefit from long-term immunomodulatory treatment. Studies prove a significant reduction of MRI brain lesions and the chance of MS attacks on interferon and Copaxone, treatment over 5 years.
Starting chronic immunomodulatory treatment in high risk optic neuritis patients is a common practice nowadays.