Understanding PIRA in Multiple Sclerosis

Progression independent of relapse activity, commonly known as PIRA in multiple sclerosis, represents a crucial challenge in modern neurotherapeutics. Historically, clinicians viewed relapsing-remitting multiple sclerosis primarily as an episodic condition driven by acute inflammatory relapses. However, cumulative clinical evidence demonstrates that insidious neurodegeneration occurs simultaneously alongside inflammatory activity from the earliest disease stages. Consequently, silent disability accumulation frequently proceeds even when patients remain entirely free from acute clinical relapses. This covert progression gradually erodes functional reserves across motor, sensory, and cognitive neurological domains. Furthermore, standard platform disease-modifying therapies, such as interferon beta, glatiramer acetate, dimethyl fumarate, and teriflunomide, primarily suppress peripheral inflammatory mechanisms. Because these classic platform agents effectively reduce focal relapses, clinicians often assumed they might also mitigate long-term progressive decline. Nevertheless, comparative real-world evidence assessing how individual platform therapies influence relapse-independent progression has remained sparse. Therefore, understanding whether specific platform agents provide superior neuroprotection has emerged as a fundamental clinical question. Evaluating these therapeutic differences ensures that neurologists establish realistic expectations and optimize long-term treatment strategies for relapsing disease.

Evaluating Platform Therapies from the Italian MS Registry

To address this knowledge gap, investigators analyzed extensive longitudinal data from the Italian MS Registry. This multicenter study evaluated 1,910 eligible patients with relapsing-remitting multiple sclerosis treated continuously for at least five years. Researchers examined two widely prescribed oral therapies, dimethyl fumarate and teriflunomide, alongside two established injectable options, interferon beta and glatiramer acetate. Furthermore, the investigators defined disability progression as confirmed functional worsening on the Expanded Disability Status Scale sustained for twelve months or longer without relapses. To prevent baseline selection bias, researchers executed rigorous 1:1 propensity score matching. Specifically, the analysis yielded 174 matched pairs comparing dimethyl fumarate against teriflunomide. Similarly, the study created 404 matched pairs comparing interferon beta against glatiramer acetate. Statistical models utilized negative binomial regression to quantify cumulative progression events over the follow-up period. Additionally, Cox proportional hazards regression assessed the time to the first confirmed progression event. Through these robust methodological controls, the study produced highly comparable treatment cohorts. Consequently, the research provides a reliable, real-world comparative assessment of whether platform disease-modifying therapies exert divergent protective effects against insidious functional decline.

Comparative Findings Across Oral and Injectable Modalities

The statistical findings revealed remarkably comparable outcomes across all matched treatment cohorts. When comparing oral treatments directly, teriflunomide demonstrated no significant difference against dimethyl fumarate regarding cumulative progression incidence, yielding a rate ratio of 0.82 with a 95% confidence interval of 0.47 to 1.40. Similarly, time to first confirmed progression did not diverge between these oral therapies, displaying a hazard ratio of 0.81 and a 95% confidence interval of 0.47 to 1.37. In the injectable comparison, glatiramer acetate showed equivalent outcomes to interferon beta. The cumulative risk ratio reached 1.04 with a 95% confidence interval of 0.74 to 1.45, while the hazard ratio was 0.86 with a confidence interval of 0.63 to 1.17. Furthermore, the researchers conducted a pooled analysis comparing all injectable therapies against oral agents. This pooled synthesis also demonstrated no statistically significant differences in cumulative progression risk (rate ratio 0.79, 95% confidence interval 0.52 to 1.19) or time to first event (hazard ratio 1.06, 95% confidence interval 0.71 to 1.58). Therefore, these empirical data demonstrate that platform therapies provide comparable protection against relapse-independent disability accumulation over long-term follow-up.

Mechanisms Underlying Smoldering Pathophysiology

To contextualize these clinical findings, clinicians must examine the underlying pathophysiological processes responsible for insidious disability worsening. Progression independent of relapse activity stems from chronic compartmentalized neuroinflammation and progressive neurodegeneration. In early relapsing disease, focal inflammatory bursts cause acute relapses and visible gadolinium-enhancing lesions on neuroimaging. However, slowly expanding lesions, smoldering microglial activation, and persistent meningeal inflammation operate behind a relatively intact blood-brain barrier. Furthermore, mitochondrial failure, axonal loss, and accelerated cerebral atrophy proceed continuously throughout the disease trajectory. Platform disease-modifying therapies exert their primary pharmacodynamic actions in the peripheral immune compartment. For example, glatiramer acetate shifts helper T cells toward anti-inflammatory profiles, while beta interferons stabilize the vascular endothelium. Teriflunomide inhibits lymphocyte proliferation, and dimethyl fumarate activates cytoprotective antioxidant pathways. While these agents suppress circulating inflammatory cascades effectively, their central nervous system penetration and microglial suppression remain relatively limited. Consequently, none of these platform agents demonstrate a distinct biological advantage in controlling central neuroinflammation. This shared pharmacological limitation explains why the study found equivalent progression rates among all four evaluated therapies.

Clinical Practice Implications and Therapeutic Decisions

Because platform therapies demonstrate equivalent efficacy against relapse-independent progression, clinicians must reconsider their treatment algorithms. Rather than assuming that switching between platform options will halt silent deterioration, physicians should prioritize safety profiles, tolerability, and patient preferences. For example, oral agents like dimethyl fumarate or teriflunomide provide convenient administration but require monitoring for gastrointestinal upset, flushing, hepatotoxicity, or lymphopenia. Conversely, injectable treatments avoid systemic organ toxicities but may induce injection-site reactions and injection fatigue. In clinical practice, routine adherence often dictates long-term therapeutic success. When patients maintain good disease control on their current platform therapy, switching to an alternative platform agent to mitigate progression lacks clinical rationale. Instead, clinicians should conduct shared decision-making discussions focusing on tolerability, lifestyle management, and vigilant disease surveillance. If confirmed progression does appear, physicians should evaluate escalation to high-efficacy therapies rather than cycling through equivalent platform drugs. High-efficacy disease-modifying agents, such as anti-CD20 monoclonals, provide greater suppression of neurodegenerative progression. Therefore, safety, tolerability, and individualized patient needs should remain the primary determinants when initiating platform therapies in multiple sclerosis.

Frequently Asked Questions

What is Progression Independent of Relapse Activity?

Progression independent of relapse activity refers to confirmed, sustained disability accumulation that develops in the complete absence of acute clinical relapses. It reflects underlying smoldering neuroinflammation, progressive axonal degeneration, and slowly expanding central lesions. This silent progression represents the primary driver of irreversible, long-term neurological disability in patients with relapsing-remitting multiple sclerosis.

Do oral platform therapies protect against PIRA better than injectables?

Large real-world registry studies show no significant difference in progression protection between oral and injectable platform therapies. Both dimethyl fumarate and teriflunomide demonstrated equivalent rates of progression when compared directly and against injectable interferons and glatiramer acetate. Consequently, treatment choices within platform therapies should depend upon patient tolerance, safety monitoring, and personal lifestyle preferences.

How should clinicians manage patients experiencing PIRA on platform DMTs?

When patients manifest insidious disability worsening without relapses while taking platform therapies, switching between equivalent platform agents provides minimal benefit. Instead, clinicians should conduct comprehensive functional assessments and consider escalating therapy to high-efficacy disease-modifying agents. These advanced therapies demonstrate superior capacity to suppress central smoldering inflammation, reduce accelerated brain volume loss, and slow permanent functional decline.

Disclaimer: This content is for informational and educational purposes only... Refer to the latest local and national guidelines for clinical practice.

References

1. Palazzo L et al. Incidence of Progression Independent of Relapse Activity (PIRA) under platform disease-modifying treatment in multiple sclerosis. J Neurol. 2026 Oct 05. doi: 10.1007/s00415-026-14171-8. PMID: 42831942.


2. Portaccio E, Bellinvia A, Fonderico M, et al. Progression independent of relapse activity in relapsing multiple sclerosis: impact and relationship with secondary progression. J Neurol. 2024;271(8):5487-5496.


3. Müller J, Sharmin S, Lorscheider J, et al. Standardized Definition of Progression Independent of Relapse Activity (PIRA) in Relapsing-Remitting Multiple Sclerosis. JAMA Neurol. 2024;81(7):722-731.