Optic neuritis is a condition that is most commonly associated with multiple sclerosis; however, it has been seen to occur independently. Dr. Alireza Minagar from Shreveport, Louisiana, who has specialized in the field of neurology and neuroimmunology has authored over 200 journals, written multiple textbook chapters, and edited various books including Multiple Sclerosis: A Mechanistic View, and Neuroinflammation, both focusing on the pathophysiology and neuroinflammation involved in MS, as well as focusing on viable therapeutic options in these conditions. He provides a brief overview of Optic Neuritis.
What is Optic Neuritis?
Optic Neuritis (ON) is defined as an inflammatory disease of the optic nerve, and it encompasses 2 different types: typical, and atypical ON. Typical ON refers to ON when it is part of a primary demyelinating disorder such as multiple sclerosis, while atypical ON occurs due to demyelination by other causes and is sometimes be harder to recover from.
In both cases, inflammation causes damage to the optic nerve, which carries signals from your eyes to the visual processing center in the brain allowing you to “see”. When damaged, patients may feel pain and have difficulty seeing out of the affected eye. Dr. Alireza Minagar points out that different parts of the optic nerve can be affected, such as the optic chiasm, which can cause symptoms in both eyes.
Neuromyelitis Optica, presents with similar vision findings, but often with spastic weakness of the lower extremities, as this condition affects the optic nerve and the spinal cord, compared to MS where the brain is involved. ON is sometimes the presenting symptom in those with MS, and Dr. Alireza Minagar emphasizes the importance of visiting a healthcare provider and being tested for MS if symptoms of ON occur.
Similar to MS, ON is generally diagnosed mostly in patients in their 20s and 30s and is more common in women than in men. The hallmark of ON is the loss of vision over a period of about a week, and it is usually associated with pain in the same eye, usually with movement, and most of the time, ON is only present unilaterally (in one eye). Some patients may have complaint of seeing flashes of light, which is not uncommon. If left untreated, vision generally will go back to normal within a few weeks, but it is highly suggested that patients seek care from their healthcare providers immediately, as sometimes intervention can help prevent permanent damage in the future.
In both typical and atypical ON, the offending factor is thought to be due to inflammation caused by an autoimmune reaction leading to demyelination of the optic nerve. Although the exact reason for the reaction is still widely unknown, it has been thought to be due to the exposure to certain viruses. The demyelination of the optic nerves causes the slowing of neural signaling, as myelin usually acts as a great nerve insulator. In MS, with slowing/loss of the nerve, there is dysfunction and eventual neurodegeneration later on in the disease process, however as mentioned, in ON it is generally self-resolving, and it is thought that remyelination occurs to help repair the damaged myelin. However, if left untreated and the patient suffers another attack, there is increased risk of permanent damage in which they could lose their vision.
Relation to Multiple Sclerosis
As a fairly common association, it has been found that those with an initial presentation of ON have up to a 35% risk of developing further MS symptoms and eventually being diagnosed, while a staggering 90% of patients with MS will experience ON at some point throughout their disease course. As both of these disorders follow a neuroinflammatory course, it is not surprising that they are closely related, and that treatment options are very similar.
A majority of ON cases tend to resolve on their own within 6–12 months, with most patients recovering completely. However, studies have found that the use of corticosteroids have helped to speed up the process, although the outcome remains the same. The go to corticosteroid has remained methylprednisolone taper dose for about 2 weeks. Another treatment option for severe cases includes the use of intravenous immune globulin (IVIG), although it is generally reserved for patients who cannot use corticosteroids, as its mechanism of action is still not fully understood, however it is known to help in the functioning of the immune system. The use of interferon-beta has also been published in literature extensively, showing a significant risk reduction in the relapse of MS related symptoms including ON. Dr. Alireza Minagar also points out that there are many novel therapy areas being researched as more information and understanding of MS, ON, and neuroinflammation in general comes out.