Multiple sclerosis is a condition of the central nervous system (CNS), which includes the brain, spinal cord, and optic nerve.
Nerves communicate with each other and with the rest of the body by sending electrical and chemical signals.
To understand how your nerves work, think about how they’re similar to electrical cables. Nerves consist of a “wire,” which we call the axon. The axon is covered by an insulating material called myelin.
MS damages the myelin so that the nerve’s ability to conduct electrical signals is slowed and uncoordinated. If the axon is also damaged, the electrical signal may be blocked entirely. When this happens, the nerve can’t send appropriate information. This produces symptoms.
- If a muscle doesn’t receive sufficient nerve input, there’s weakness.
- If the part of the brain that’s responsible for coordination is damaged, this can cause tremors or loss of balance.
- Lesions, or areas of nerve damage, in the optic nerve may result in vision loss.
- Spinal cord damage is usually associated with decreased mobility, impaired or abnormal sensations, and impaired genitourinary (genital and urinary) function.
When it comes to the brain, changes due to MS can contribute to fatigue and other symptoms. Brain lesions can produce difficulty with thinking and memory. MS brain changes may also contribute to mood disorders such as depression.
MS is widely believed to be an autoimmune process. In other words, the immune system, which normally protects your body, goes “rogue” and begins to attack parts of your body.
In MS, the immune system attacks nerves in the CNS.
The Food and Drug Administration (FDA) has approved more than 20 different medications — known as disease-modifying therapies (DMTs) — that can limit the number of new lesions due to MS.
The most important strategies that have been documented for reducing future nerve damage are early diagnosis and timely treatment with these medications.
Lifestyle habits such as exercising regularly, not smoking, and maintaining a moderate body weight are also important.
MS produces damage in the more heavily myelinated regions of the brain, known as white matter. MS has also been shown to affect the less myelinated regions closer to the surface of the brain, known as cortical gray matter.
Damage to both white matter and gray matter structures are linked to cognitive impairment. Damage to specific brain regions can produce difficulty with specific cognitive skills.
The rate of brain atrophy, or shrinkage, in people with MS has been shown to be
People with MS who smoke tobacco have been
There are also reports that people with MS who are more physically active have less atrophy than people who are less physically active.
The cognitive difficulties that are most common in people with MS tend to be related to memory and speed of information processing.
There may also be problems with:
- sustained memory and concentration
- decision making
Additionally, difficulty with verbal fluency, especially word finding — the feeling that “the word is on the tip of my tongue” — is common.
Cognitive difficulties may be a direct result of lesions. Cognition may also be impaired by one or more of these contributing factors:
- poor sleep
- the effects of medication
Some cognitive functions are more likely than others to remain healthy. General intelligence and information, and understanding of words, tend to be preserved.
Different cognitive functions tend to be associated with different parts of the brain, although there’s a lot of overlap.
So-called “executive functions” — such as multitasking, prioritizing, and decision making — are most associated with the frontal lobes of the brain.
Many memory functions occur in a gray matter structure called the hippocampus. Its name comes from the Greek word for seahorse.
Damage to the corpus callosum, a very heavily myelinated bundle of nerves that connects the two hemispheres of the brain, is also associated with cognitive impairment.
MS commonly affects all of these areas.
Overall brain atrophy and loss of brain volume are also highly correlated with cognitive function issues.
There are short tests of specific cognitive functions that can be easily and quickly administered in a doctor’s office. These can help screen for evidence of cognitive impairment. For example, one such test is called the Symbol Digit Modalities Test (SDMT).
If a screening test suggests cognitive problems, your doctor may recommend a more in-depth assessment. This would usually be formally done with tests that are collectively referred to as neuropsychological testing.
It’s recommended that people with MS be assessed for cognitive function at least once per year.
When addressing cognitive impairment in people with MS, it’s important to identify any contributing factors, such as fatigue or depression, that may worsen cognitive problems.
People living with MS may have untreated sleep disorders such as sleep apnea. This can also affect cognition. When these secondary factors are treated, cognitive function often improves.
Research has shown that targeted cognitive rehabilitation strategies are beneficial. These strategies address specific domains — such as attention, multitasking, processing speed, or memory — using techniques such as computer training.
A growing body of literature suggests that regular physical exercise may improve cognitive function in people with MS.
While no diet has been shown to affect cognition in people with MS per se, a heart-healthy diet may reduce the risk of comorbidities (other diseases) that can contribute to cognitive impairment.
A heart-healthy diet is generally one that primarily contains lots of fruits and vegetables, lean proteins, and “good” fats such as olive oil. The diet should also limit saturated fats and refined sugars.
Following this type of eating plan may limit comorbidities such as vascular disease, type 2 diabetes, or high blood pressure. All of these conditions can contribute to cognitive impairment and disability in people with MS.
Smoking is a risk factor for brain atrophy, so quitting smoking may help to limit further atrophy.
It’s also important to stay mentally active and socially connected.
Editor’s note: This article was originally published on June 12, 2019. Its current publication date reflects a medical review.
Barbara S. Giesser, MD received her medical degree from the University of Texas Health Science Center at San Antonio, and completed neurology residency training and MS fellowship at the Montefiore Medical Center (NY) and Albert Einstein College of Medicine. She’s specialized in the care of persons with MS since 1982. She’s currently Professor of Clinical Neurology at the David Geffen UCLA School of Medicine and Clinical Director of the UCLA MS program.
Dr. Giesser has conducted peer-reviewed research into the effects of exercise in persons with MS. She’s also created educational curricula for national organizations such as the National MS Society and the American Academy of Neurology. She’s active in advocacy efforts to promote access to care and medications for persons with MS and other neurologic diseases.