Best Practices
The Multiple Sclerosis Centers of Excellence: A Model of Excellence in the VA
The MS Centers of Excellence at the VA improves the consistency and quality of care for veterans with MS.
Multiple sclerosis (MS) is the most common demyelinating disease of the central nervous system, with recent estimates of around 1 million people living with MS in the US.1 In many countries, MS is a leading cause of disability among young adults, second only to trauma.2 Clinically, neurologic worsening (ie, disability) in MS can occur in the relapsing-remitting (RRMS) phase of disease due to incomplete recovery from neuroinflammatory relapses. However, in the 15% of patients with a progressive course from onset (PPMS), and in those with RRMS who transition to a secondary progressive phenotype (SPMS), neurologic worsening follows a slowly progressive pattern.3 A progressive disease course—either PPMS at onset or transitioning to SPMS—is the dominant factor affecting MS-related neurologic disability accumulation. In particular, epidemiologic studies have shown that, in the absence of transitioning to a progressive disease course, < 5% of individuals with MS will accumulate sufficient disability to necessitate use of a cane for ambulation.4-6 Therefore, developing disease modifying therapies (DMTs) that are highly effective at slowing or stopping the gradual accumulation of neurologic disability in progressive MS represent a critical unmet need.
Research into the development of DMTs for progressive MS has been hindered by a number of factors. In particular, the clinical definition and diagnosis of progressive MS has been an evolving concept. Diagnostic criteria for MS, which help facilitate the enrollment of appropriate subjects into clinical trials, have only recently clarified the current consensus definition for progressive MS—steadily increasing neurologic disability independent of clinical relapses. Looking back to the Schumacher criteria in 1965 and Poser criteria in 1983, it was acknowledged that neurologic symptoms in MS may follow a relapsing-remitting or progressive pattern, but little attempt was made to define progressive MS.7,8 The original McDonald criteria in 2001 defined diagnostic criteria for progressive MS.9 These criteria continued to evolve through subsequent revisions (eg, cerebrospinal fluid [CSF] specific oligoclonal bands no longer are an absolute requirement), and only in the 2017 revision was it emphasized that disability progression must occur independent of clinical relapses, concordant with similar emphasis in the 2013 revision of MS clinical course definitions.3,10
The interpretation of prior clinical trials of DMT for progressive MS must consider this evolving clinical definition. The US Food and Drug Administration (FDA) approved mitoxantrone in 2000—making it the first DMT to carry an approved label for SPMS. While achieving significant clinical efficacy, it is clear from the details of the trial that the enrolled subjects had a high degree of inflammatory disease activity, which suggests that mitoxantrone treats neuroinflammation and not relapse-independent worsening. More recently, disparate results were seen in the anti-CD20 (rituximab, ocrelizumab) and S1P receptor modulator (fingolimod, siponimod) trials targeted at patients with primary and secondary progressive MS.11-14 Although there are differences between these therapies, they are more similar than not within the same therapeutic class. Taken together, these trials illustrate the critical impact the narrower inclusion/exclusion criteria (namely age and extent of inflammatory activity) had on attaining positive outcomes. Other considerations, such as confounding illness, also may impact trial recruitment and generalizability of findings.
The lack of known biological targets in progressive MS, which is a complex disease with an incompletely understood and heterogeneous pathology, also hinders DMT development. Decades of research has characterized multifocal central nervous system (CNS) lesions that exhibit features of demyelination, inflammation, reactive gliosis, axonal loss, and neuronal damage. Until recently, however, much of this research focused on the relapsing phase of disease, and so the understanding of the pathologic underpinnings of progressive disease has remained limited. Current areas of investigation encompass a broad range of pathological processes, such as microglial activation, meningeal lymphoid follicles, remyelination failure, vulnerability of chronically demyelinated axons, oxidative injury, iron accumulation, mitochondrial damage, and others. There is the added complication that the pathologic processes underlying progressive MS are superimposed on the CNS aging process. In particular, the transition to progressive MS and the rate of disability accumulation during progressive MS show strong correlation with age.6,15-17
Finally, DMT development for progressive MS also is hindered by the lack of specific surrogate and clinical outcome measures. Trials for relapsing MS have benefited greatly from the relatively straightforward assessment of clinical relapses and inflammatory disease activity on magnetic resonance imaging (MRI). With the goal of developing DMTs that are highly effective at slowing or stopping the gradual accumulation of neurologic disability in progressive MS, which by definition occurs independent of clinical relapses, these measures are not directly relevant. The longitudinal clinical disability outcome measures change at a slower rate than in early, relapsing disease. The use of standardized scales (eg, the Expanded Disability Status Scale [EDSS]), lower limb function, upper limb function, cognition, or a combination is a subject of ongoing debate. For example, the ASCEND and IMPACT trials (placebo-controlled trials for SPMS with natalizumab and interferon β-1a, respectively) showed no significant impact in EDSS progression—but in both of these trials, the 9-hole peg test (9-HPT), a performance measure for upper limb function, showed significant improvement.10,18 Particularly in those with an EDSS of > 6.5, who are unlikely to have measurable EDSS progression, functional tests such as the 9-HPT or timed 25-foot walk may be more sensitive as measures for disability progression.11 MRI measures of brain atrophy is the current gold standard surrogate outcome for clinical trials in progressive MS, but others that may warrant consideration include optical coherence tomography (OCT) or CSF markers of axonal degeneration.