Primary Progressive MS Facts and Statistics: What You Need to Know

Primary progressive multiple sclerosis, or PPMS, is a relatively rare type of multiple sclerosis characterized by slowly worsening symptoms and disability over time. It affects around 10% to 15% of people living with MS.

PPMS tends to involve the spinal cord more than the brain, resulting in leg weakness, walking difficulties, and significant fatigue.

This article will review key facts and statistics about PPMS, a highly variable and unpredictable disease.

Primary Progressive MS Overview

In MS, the immune system malfunctions and damages the fatty myelin sheath covering and protecting nerve fibers within the central nervous system (CNS). The CNS is made up of your brain, spinal cord, and the optic nerves of your eyes.

When myelin is damaged, nerve signaling is interrupted, causing various symptoms like vision changes, numbness, pain, weakness, and muscle stiffness. 

People with PPMS experience worsening neurological symptoms from the onset of their disease. This is in contrast to most others with MS who experience symptom flare-ups (relapses) followed by periods of symptom recovery (remission).

Like other types of MS, PPMS is incurable. Although, an approved disease-modifying therapy (DMT) called Ocrevus (ocrelizumab) can help slow the disease down.

How Common Is PPMS?

The estimated prevalence of MS in the United States is nearly 1 million adults. Since PPMS occurs in around 10% to 15% of people with MS, the approximate prevalence of PPMS in the United States is 100,000 to 150,000 adults.

The estimated number of individuals with MS worldwide is 2.8 million. This has increased from 2.3 million in 2013.

PPMS by Ethnicity

MS, including PPMS, affects most racial and ethnic groups. While believed to most commonly affect people of White northern European backgrounds, emerging research suggests that MS prevalence may be similar in White and Black Americans.

Specifically, one California study reported MS prevalence to be around 0.2% among both Black and White Americans and significantly lower among Hispanic and Asian Americans (0.06% and 0.02%, respectively).

It's unclear if MS rates are increasing in the Black population or if the disease was under-recognized in the past. Understanding racial differences in MS is key to optimizing care for all patients.

PPMS by Age and Gender

PPMS typically manifests at an older age (mid-40s on average) compared to those with relapsing-remitting MS (RRMS).

PPMS can develop in childhood, although this is extraordinarily rare. Only 2%–5% of MS cases are diagnosed before the age of 18 (pediatric MS), and of those, it's believed that less than 1%–7% will develop into PPMS.

Regarding sex differences, PPMS is the only type of MS that is not female predominant. Rather, PPMS affects all sexes equally.

Interestingly, while males are less likely overall to develop MS than females, if they do develop it, they have a higher chance of having PPMS. Males with PPMS, however, do not have a worse disease outlook than females with RRMS.

Causes of PPMS and Risk Factors

As with other types of MS, the precise cause of PPMS remains unknown. Current research suggests that PPMS involves a neurodegenerative ("nerve dying") process driven by malfunctioning B cells.

Specifically, experts suspect that once a certain age threshold is reached, genetically susceptible individuals who were previously infected with the Epstein-Barr virus (EBV) may develop PPMS.

Besides genes, age, and prior EBV infection, other factors or theories that may influence PPMS manifestation include:

• Your gut microbiome (the organisms that live in your digestive tract)
• Iron accumulation in your brain
• Dysfunction of mitochondria (the "powerhouse" or energy-producing parts of cells)

What Are the Mortality Rates for PPMS?

The mortality rate in those with MS is increased compared to people of the same age in the general population.

Compared to those with relapsing-remitting MS, people with PPMS have an even higher mortality rate.

In a 2017 study, investigators found that people with PPMS had around a 10-year shorter life span than the general population. Moreover, the age at which those with PPMS die (called survival age) is six years less than those with relapsing-remitting MS. 

While mortality rates are higher in patients with PPMS, research suggests that only about half of all deaths in patients with MS are related to the disease itself. Many people with MS die from the same causes as those in the general population (e.g., cancer, heart disease, and stroke).

Screening and Early Detection

There is no way to screen for or prevent PPMS. PPMS is a complex disease that likely involves multiple factors out of your control (your genetic makeup, for example). While certain lifestyle factors, notably smoking and obesity, have been found to influence disease activity in people with RRMS, this is not true in individuals with PPMS.  

The criteria for diagnosing PPMS are also different from other forms of MS.

For a diagnosis of PPMS, there must be evidence of disease progression over one year, along with two of the following:  

• A brain MS lesion (area of inflammation related to MS) seen on magnetic resonance imaging (MRI)
• Two or more spinal cord MS lesions seen on MRI
• Evidence of oligoclonal band or an increased IgG (immunoglobulin G) level in the cerebrospinal fluid (both are proteins that indicate inflammation) obtained during a lumbar puncture (also called a spinal tap)
  

Summary

Almost 1 million adults in the United States are living with multiple sclerosis, and around 10% to 15% of those have primary progressive MS (PPMS). PPMS is a unique type of MS associated with worsening neurological symptoms and disability from the start of the disease.

PPMS occurs across most racial and ethnic groups and appears to occur equally in people of all sexes. Like other forms of MS, PPMS is associated with a slightly shorter life span.