How Multiple Sclerosis Impacts the Brain and Cognitive Function

What Is Multiple Sclerosis?

Multiple sclerosis (MS) is a chronic disease of the central nervous system (CNS) that affects the brain, spinal cord, and optic nerves. It can produce a wide range of physical and cognitive symptoms.

How MS Damages Nerve Fibers

Neurons transmit signals through an axon, which is insulated by a fatty sheath called myelin. In MS the immune system mistakenly attacks myelin, slowing or blocking electrical signals. When the axon itself is injured, signal transmission can stop completely.

Neurological Symptoms Linked to Lesion Location

• Damage to motor areas → muscle weakness.
• Involvement of cerebellar pathways → tremor, loss of balance.
• Optic‑nerve lesions → blurred vision or vision loss.
• Spinal‑cord injury → reduced mobility, abnormal sensations, and bladder or sexual dysfunction.

Cognitive and Mood Effects

Brain lesions often lead to fatigue, memory problems, slowed information processing, and difficulty multitasking. Mood disorders such as depression are also common.

Underlying Autoimmune Process and Approved Therapies

MS is considered an autoimmune disease: the immune system “goes rogue” and attacks CNS myelin. The U.S. Food and Drug Administration has approved more than 20 disease‑modifying therapies (DMTs) that reduce the formation of new lesions. Early diagnosis and timely treatment are the most effective ways to limit nerve damage.

White‑Matter vs. Gray‑Matter Damage

MS primarily targets heavily myelinated white‑matter tracts, but it also affects cortical gray matter near the brain’s surface. Injury to both tissue types is associated with cognitive decline, especially in language, calculation, memory, and attention.

Brain Atrophy and Modifiable Risk Factors

People with MS experience faster brain‑volume loss than age‑matched controls. Smoking accelerates atrophy, whereas regular physical activity and some DMTs may slow it. Maintaining a healthy weight and avoiding tobacco are therefore crucial.

Common Cognitive Challenges

• Reduced processing speed and memory.
• Difficulty with multitasking, prioritizing, and decision‑making.
• Poor sustained attention and organization.
• Word‑finding problems (“tip‑of‑the‑tongue” phenomenon).

Fatigue, poor sleep, depression, and medication side‑effects can worsen these issues, while intelligence and basic language comprehension are usually preserved.

Assessment and Monitoring

Brief office‑based tests such as the Symbol Digit Modalities Test (SDMT) can screen for cognitive impairment. If a problem is detected, a full neuropsychological evaluation is recommended. Annual cognitive screening is advised for all people with MS.

Management Strategies

• Targeted cognitive rehabilitation (computer‑based training for attention, memory, processing speed).
• Regular aerobic exercise, which has been shown to improve cognition.
• A heart‑healthy diet rich in fruits, vegetables, lean protein, and unsaturated fats to reduce vascular comorbidities.
• Smoking cessation to limit further brain atrophy.
• Maintaining social connections and mental engagement.

Prognosis

Modern therapies have narrowed the life‑expectancy gap. A 60‑year longitudinal study (2017) reported a median lifespan of 74.7 years for people with MS versus 81.8 years for the general population. Men with MS lived a median of 72.2 years, women 77.2 years.

Treatment Options

• Injectable DMTs (e.g., beta‑interferons).
• Oral agents such as cladribine (Mavenclad) or fingolimod (Gilenya).
• Infusion therapies including ocrelizumab (Ocrevus) or natalizumab (Tysabri).

When to Seek Medical Evaluation

If you experience any combination of the following, contact a neurologist promptly:

• Persistent fatigue or weakness.
• Walking difficulties.
• Sensations of tightness around the torso.
• Muscle stiffness or spasms.
• Vision changes.
• Bladder, bowel, or sexual dysfunction.
• Pain, itching, or emotional/cognitive shifts.

Editor’s note: This article was originally published on June 12, 2019. The current date reflects a recent medical review.

Dr. Barbara S. Giesser, MD, received her medical degree from the University of Texas Health Science Center at San Antonio, completed a neurology residency and MS fellowship at Montefiore Medical Center and Albert Einstein College of Medicine, and has specialized in MS care since 1982. She is a Professor of Clinical Neurology at UCLA David Geffen School of Medicine and Clinical Director of the UCLA MS program. Dr. Giesser’s research focuses on exercise effects in MS, and she has contributed to educational curricula for the National MS Society and the American Academy of Neurology, as well as advocacy for access to care.