What Is SPMS (Secondary Progressive Multiple Sclerosis)?

SPMS stands for secondary progressive multiple sclerosis, a phase of MS in which disability accumulates gradually and steadily rather than arriving in the distinct flare-ups that characterize the earlier relapsing-remitting stage. Most people with MS start with that relapsing-remitting pattern, and roughly half transition to SPMS within twenty years of their initial diagnosis.¹ The shift is not a sudden event but a slow drift, often recognized only in hindsight, and it changes both the daily experience of living with MS and the treatment strategies that are likely to help.

How SPMS Differs From Relapsing-Remitting MS

In relapsing-remitting MS (RRMS), the disease shows up as episodes: a person might develop blurred vision, numbness, or difficulty walking for days or weeks, then recover partially or fully before the next episode. Between relapses, the disease can appear stable. SPMS is what happens when that pattern gives way to a slow, continuous worsening of neurological function that is independent of individual relapses.² A person with SPMS may still have occasional relapses on top of that steady decline, but the defining feature is disability progression that marches on regardless of whether a relapse has occurred.

This distinction matters for treatment. Most of the disease-modifying therapies that work well for RRMS target the immune system’s episodic attacks on myelin, the protective sheath around nerve fibers. In SPMS, the damage increasingly comes from smoldering neurodegeneration inside the brain and spinal cord, processes that those same drugs have limited power to slow.³

Why It Takes So Long to Diagnose

One of the most frustrating aspects of SPMS is that it is almost always diagnosed after the fact. There is no single blood test, brain scan, or clinical marker that definitively announces the transition from RRMS to SPMS. Instead, a neurologist looks backward at a patient’s records and realizes that disability has been creeping upward for months or years without being driven by clear relapses.⁴ Diagnosis is often delayed by about three years from when the transition actually began, partly because the early signs of progression are subtle and partly because there are no agreed-upon diagnostic criteria.⁵

That delay has real consequences. Treatments that target the progressive phase work best when started early, and a three-year lag means people may spend years on therapies better suited to the relapsing phase while the window for more appropriate intervention narrows.

What Is Happening Inside the Brain

The biology of SPMS looks quite different from what drives RRMS. In the relapsing phase, waves of immune cells breach the blood-brain barrier and attack myelin in distinct, focal lesions. In SPMS, the inflammation becomes more compartmentalized: it settles behind the blood-brain barrier and becomes harder to reach with conventional immune-suppressing drugs. A key finding in post-mortem brain studies is that the meninges, the membranes surrounding the brain, harbor clusters of B cells and T cells. In one study, follicle-like B-cell structures were found in the inflamed meninges of over half of SPMS cases examined, and their presence tracked with more severe cortical thinning and neuron loss in the underlying brain tissue.⁶

That meningeal inflammation sets off a cascade. Microglia, the brain’s resident immune cells, become chronically activated, and the damage they inflict on neurons and their connections drives much of the progressive disability. Research has shown that the density of activated microglia rises in a gradient from the surface of the brain inward, suggesting the inflammation in the meninges is directly seeding damage deeper in the cortex.⁷ This smoldering process explains why brain atrophy, meaning measurable shrinkage of brain tissue, accelerates in SPMS compared to the relapsing phase.

Active Versus Non-Active SPMS

Neurologists now classify SPMS into subtypes based on whether there is ongoing inflammatory activity. “Active” SPMS means the person still has relapses or new/enlarging lesions visible on MRI, on top of the steady progression. “Non-active” SPMS means progression continues without those inflammatory flare-ups. You might expect active SPMS to move faster, since there seems to be more disease happening at once. But data from a large Italian registry study found that the rates of disability progression independent of relapses were similar in both groups: about 27% of active and 30% of non-active SPMS patients showed confirmed disability worsening at two years.⁸

The practical takeaway is that the underlying progressive mechanism grinds on at a roughly consistent pace regardless of whether inflammatory attacks are still happening. The active subtype does matter for treatment decisions, though, since some therapies specifically target the inflammatory component and may reduce relapses even if they do not halt the progressive decline.

Emerging Ways to Spot the Transition Earlier

Because the retrospective nature of diagnosis is such a problem, researchers have been working to find objective markers that could flag the transition to SPMS in real time. Two main avenues are showing promise: advanced brain imaging and blood-based biomarkers.

On the imaging side, MRI techniques are now sensitive enough to detect features closely associated with SPMS, including slowly expanding lesions (existing lesions that gradually grow at their edges), iron rim lesions (chronic lesions surrounded by iron-laden activated microglia), gray matter atrophy, and overall brain volume loss.⁹ The presence of slowly expanding lesions on MRI, along with thinning of retinal layers seen on optical coherence tomography, has been identified as a helpful diagnostic indicator for SPMS.¹⁰

On the blood side, a protein called GFAP (glial fibrillary acidic protein) is drawing attention. GFAP is released by astrocytes, the brain’s support cells, when they are under stress. Researchers found that higher serum GFAP levels were linked to a higher risk of confirmed disability progression in people with progressive MS, with a hazard ratio of about 1.7. The association was even stronger in patients whose disease showed low inflammatory activity, suggesting GFAP reflects the smoldering, non-relapse-driven damage that defines SPMS.¹¹ GFAP appears to be complementary to another well-known biomarker, neurofilament light chain (NfL), which is more closely tied to the acute nerve damage that happens during relapses and new lesion formation.¹²

Cognitive Effects

Physical disability is what most people associate with MS progression, but cognitive decline in SPMS is common and can be just as disabling. In one study of SPMS patients, the frequency of measurable cognitive decline was 80%.¹³ The cognitive domains most affected tend to be information processing speed, working memory, verbal fluency, and episodic verbal memory, and the severity of these problems is generally worse in SPMS than in RRMS.¹⁴

These are not the kinds of cognitive lapses everyone experiences with age. Slowed processing speed means conversations move too fast, multitasking becomes genuinely difficult, and tasks at work that used to be routine now require concentrated effort. That same study found that processing speed and memory scores were the strongest predictors of employment status, and that atrophy of the corpus callosum, the thick bundle of nerve fibers connecting the two brain hemispheres, was the MRI feature most tightly linked to those deficits.¹⁵

Treatment Options

For years, there was essentially nothing proven to slow disability progression in SPMS. That changed with the approval of siponimod, a drug that modulates specific receptors on immune cells. In the pivotal EXPAND trial, siponimod reduced the risk of confirmed disability progression over three months by about 21% compared to placebo.¹⁶ Longer-term follow-up data over five years showed a sustained reduction: continuous siponimod cut the risk of six-month confirmed disability progression by about 22% and also slowed brain atrophy and relapse rate.¹⁷

A 21-22% risk reduction is meaningful but modest, and it underscores how hard progressive MS is to treat. Much of the research community’s hope is pinned on a newer class of drugs called BTK inhibitors (Bruton’s tyrosine kinase inhibitors). These drugs can cross the blood-brain barrier and act on microglia and B cells directly inside the central nervous system, which is exactly where the smoldering inflammation in SPMS lives. In animal models that mimic the progressive phase, BTK inhibition reduced disease severity, decreased demyelination, and lowered the number of inflammatory cells in the spinal cord.¹⁸ Several BTK inhibitors are in clinical trials for progressive MS, and results over the next few years should clarify whether this promise translates to human benefit.

Neuropathic pain is a common symptom in SPMS, and managing it remains difficult. A well-designed trial tested three repurposed drugs, fluoxetine, riluzole, and amiloride, for SPMS-associated neuropathic pain and found none of them performed better than placebo.¹⁹ Standard neuropathic pain medications like gabapentin and pregabalin are still used, but the evidence base for their effectiveness specifically in SPMS is thin.

What Influences How Fast SPMS Progresses

Several factors appear to affect both the likelihood of transitioning to SPMS and how quickly disability accumulates once you are in the progressive phase. A long-term study of MS natural history found that male sex, older age at MS onset (over 30), and a high number of relapses in the first few years all predicted a faster transition to SPMS and shorter times to severe disability milestones.²⁰ An interesting nuance from the same study: the duration of the relapsing phase before progression began did not influence how fast the progressive phase itself moved. In other words, whether someone transitions to SPMS after five years or fifteen, the speed of decline once progression starts tends to follow its own trajectory.

Modifiable risk factors also matter. A systematic review of 59 studies found that smoking was associated with faster MS progression, with smokers facing roughly 55% higher risk of disability worsening. Lower vitamin D levels were also consistently linked to higher disability scores.²¹ The smoking risk appears dose-dependent: one study found that smoking more than ten cigarettes a day more than doubled the risk of developing SPMS even after adjusting for age, sex, and relapse rate.²²

The Role of Rehabilitation and Exercise

Physiotherapy and exercise are not going to reverse the neurodegeneration in SPMS, but the evidence suggests they can meaningfully improve function and quality of life. A systematic review of physiotherapy interventions for progressive MS found that almost every study examined produced positive results on at least one outcome measure, including benefits from exercise therapy, multidisciplinary rehabilitation programs, functional electrical stimulation, and body-weight-supported treadmill training.²³ The authors cautioned that most of these studies were small and underpowered, but the consistency of positive signals across different types of interventions is encouraging.

Fatigue is one of the most debilitating symptoms in SPMS, and a small pilot study testing a multimodal intervention that combined dietary changes, exercise, neuromuscular electrical stimulation, and stress management found a substantial drop in fatigue scores over 12 months.²⁴ As a small, uncontrolled study it cannot prove causation, but it points toward an area that deserves larger trials. For people living with SPMS, staying as physically active as possible, with appropriate adaptations, remains one of the most actionable recommendations available.

The Concept of PIRA and Why It Is Reshaping the Field

A concept that has transformed how researchers think about SPMS is PIRA, which stands for progression independent of relapse activity. For a long time, disability worsening in MS was assumed to come from incomplete recovery after relapses. PIRA flips that assumption: it is disability that accumulates without any identifiable relapse driving it. A large study of over 16,000 patients found that among those who experienced sustained PIRA, about 73% eventually transitioned to a formal SPMS diagnosis.²⁵

PIRA is important because it can be detected while a person still carries an RRMS diagnosis. If your disability score keeps ticking upward between relapses, even in small increments, that silent worsening may be a signal that the biology of progression is already active beneath the surface. Identifying PIRA early could shorten that three-year diagnostic lag and open a window for earlier intervention with therapies that target the progressive mechanism.

Financial and Personal Burden

SPMS carries a heavy economic and personal toll. A Spanish study estimated the total annual cost per person with SPMS at roughly €41,500 (about $45,000), with over half of that attributable to indirect costs like lost earnings and caregiver time rather than medical bills. More than 90% of participants were no longer working, and nearly 80% had taken early retirement.²⁶ An Italian study similarly found that healthcare costs for SPMS patients were roughly double those for RRMS patients, whether or not they were on disease-modifying therapy.²⁷

Beyond the numbers, the practical reality is that 80% of people with SPMS in the Spanish cohort needed help with domestic tasks, and nearly half used daycare or rehabilitation center services.²⁸ The burden on informal caregivers, usually family members, is enormous and largely invisible in healthcare budgets. Planning early for workplace accommodations, disability benefits, and home modifications can make the transition more manageable, even though those conversations are difficult to initiate while a person is still functioning well.