Multiple Sclerosis: Types, EDSS Scale, and DMT Comparison

An Immune System Attacking the Wrong Target

Multiple sclerosis affects approximately 2.8 million people worldwide, with incidence roughly twice as high in women as in men. The disease involves autoreactive T lymphocytes and B cells breaching the blood-brain barrier and attacking the myelin sheaths that insulate central nervous system axons. When myelin is stripped, nerve conduction slows or fails entirely, producing the characteristic episodes of neurological dysfunction — vision loss, limb weakness, sensory disturbances, balance problems — that define the disease. Over time, axonal damage accumulates even during periods of clinical stability, driving irreversible disability.

Geography matters profoundly. MS prevalence exceeds 200 per 100,000 population in northern latitudes (Canada, Scandinavia, northern U.S.) but falls below 5 per 100,000 near the equator. Vitamin D deficiency, latitude-associated sun exposure, and Epstein-Barr virus (EBV) infection are the strongest environmental risk factors identified. A landmark 2022 study in Science by Kjetil Bjornevik et al. using 10 million U.S. military personnel records found that EBV seropositivity preceded MS onset in 32 of 33 cases, supporting a causal link.

MS Subtypes

• Relapsing-remitting MS (RRMS): Affects approximately 85% of patients at diagnosis. Defined by discrete attacks (relapses) with full or partial recovery between episodes. MRI shows new or enlarging T2 lesions and gadolinium-enhancing active lesions during relapses
• Secondary progressive MS (SPMS): Most RRMS patients eventually transition to SPMS, characterized by steady disability worsening independent of clinical relapses. The conversion rate was historically 50% at 10 years, but is lower in the DMT era
• Primary progressive MS (PPMS): Affects ~15% of patients; steady worsening from onset without distinct relapses. Historically had no approved treatments until 2017
• Clinically isolated syndrome (CIS): First demyelinating episode; 50–70% develop MS within 10 years if MRI shows characteristic lesions (McDonald criteria)

The Expanded Disability Status Scale

The EDSS, developed by John Kurtzke in 1983, remains the standard disability measure in MS clinical trials despite well-documented limitations. It runs from 0 (normal neurological exam) to 10 (death due to MS), with half-point increments.

Disease-Modifying Therapy: Three Generations

DMT development has transformed MS management since 1993, when interferon beta-1b became the first approved therapy. The field has since stratified into efficacy tiers, with higher efficacy coming at the cost of greater risk.

Natalizumab and the JC Virus Risk

Natalizumab (Tysabri) blocks the alpha-4 integrin adhesion molecule, preventing lymphocytes from crossing the blood-brain barrier. In the AFFIRM trial it reduced annualized relapse rate by 68% and new MRI lesions by 83% — then the most effective MS therapy. But sustained use reactivates John Cunningham virus (JCV), a common polyomavirus carried latently by 50–60% of adults. Reactivation can cause progressive multifocal leukoencephalopathy (PML), a frequently fatal or severely disabling brain infection.

• PML risk is stratified by JCV antibody index, prior immunosuppressant use, and treatment duration
• Patients negative for JCV antibodies carry very low PML risk (<1:10,000) and can safely use natalizumab
• In JCV-positive patients with index >1.5 treated >24 months, PML risk approaches 1:100
• Extended interval dosing (every 6 weeks instead of 4) reduces PML risk by approximately 94% without substantially compromising efficacy

Ocrelizumab: The PPMS Breakthrough

Ocrelizumab (Ocrevus), a humanized anti-CD20 monoclonal antibody that depletes B cells, received FDA approval in March 2017 for both RRMS and PPMS — the first therapy ever approved for primary progressive disease. In the ORATORIO trial in PPMS, ocrelizumab reduced 12-week confirmed disability progression by 24% relative to placebo. In RRMS, the OPERA I and II trials demonstrated 46–47% relapse rate reduction vs. interferon beta-1a.

The anti-CD20 class has since expanded to include ofatumumab (Kesimpta), a fully human subcutaneous self-injection approved in 2020, and ublituximab (Briumvi), approved in 2022 with a 1-hour infusion time. Long-term concerns center on hypogammaglobulinemia from sustained B-cell depletion, increasing infection risk after cumulative exposure. Recommendations advise completing all vaccinations before starting anti-CD20 therapy, as vaccine responses are markedly blunted during treatment.

This article is for informational purposes only. Consult a qualified healthcare professional.