MS is an autoimmune disease with an unknown etiology, or "cause". It is believed that some type of environmental factor (a virus, maybe) can provoke the immune system to start creating antibodies against the myelin covering of the nerves and nerve tracts, thus the onset of MS. Brain plaques are places that experience destruction of the nerves’ coverings, or sheath. Most often during MS, the vision is affected in a condition that doctors have called "retro-bulbar neuritis" In fact, retro-bulbar neuritis is the most common manifestation of MS. Urinary incontinency is a rarely a manifestation of MS. Plaques during MS can be seen via CT-scan or MRI. Other than plagues, a person also experiences an increased amount of immunoglobulins in the cerebrospinal liquid. MS is mainly a progressive disease with incomplete remissions.

Meningitis, on the other hand, is an inflammation of the brain coverings. Viral meningitis is not so severe a disease as the bacterial variety. Viral meningitis is rarely accompanied with brain inflammation (meningoencephalitis).

Encephalitis is a severe acute inflammation of the brain or spinal cord (myelitis) caused by viruses or an allergic reaction to some types of infections. Viruses that can cause encephalitis could be: arbo-viruses, polio, ECHO, and rabies A so called "secondary post-infective encephalitis" also exists which is due to an allergic reaction to infections with other viruses such as measles, chickenpox, smallpox, influenza, mumps, or herpes simplex. Similar occurrences of encephalitis can occur after vaccination against smallpox or rabies. These types of encephalitis cause demyelinization (damaging the myelin nerves’ covering) that are also present during multiple sclerosis.