The Future of Progressive Multiple Sclerosis Therapies
Introduction: Multiple sclerosis (MS) affects more than a million people in the US. A considerable portion of these patients either begin with primary progressive disease or eventually transition to secondary progressive MS. A progressive disease course is the most critical factor affecting disability accumulation. The relatively recent development of treatments for relapsing multiple sclerosis has had a profound impact on the disease course for many with MS. Unfortunately, therapies for progressive MS have not had the same degree of advancement in general. New insights into the pathophysiology of progressive MS may lead to new treatments.
Observations: In this review, we identify some of the significant challenges encountered in the development of therapies for progressive MS, assess the evidence for use of currently approved therapies for patients with progressive MS, identify some of the current therapies in development from progressive MS, and consider the role for discontinuing therapy in certain patients.
Conclusions: Developing effective disease modifying therapies that slow or stop the gradual accumulation of neurologic disability in progressive MS represents a critical unmet need. As the understanding of the inflammatory and neurodegenerative aspects of MS are better elucidated there may be opportunity for advancement in the treatment of progressive MS.
Discontinuing DMT
In the early 1990s, the successful development of immune modulating therapies that reliably reduced disease activity in RRMS led to widespread initiation in patients with relapsing disease. However, guidance on when or if to discontinue DMT, even in those who have transitioned to SPMS, remains largely absent at this time. Requests to discontinue DMT may come from patients weary of taking medication (especially injections), bothered by AEs, or those who no longer perceive efficacy from their treatments. Clinicians also may question the benefit of immune modulation in patients with longstanding freedom from relapses or changes in MRI lesion burden.
To inform discussion centered on treatment discontinuation, a clinical trial is currently underway to better answer the question of when and how to withdraw MS therapy. Discontinuation of Disease Modifying Therapies in Multiple Sclerosis (DISCO-MS) is a prospective, placebo-controlled RCT and its primary endpoint is recurrence of disease activity over a 2 year follow-up period.37 Eligibility requirements for the trial include age > 55 years, 5-year freedom from relapses, and 3-year freedom from new MRI lesions (criteria informed by progressive MS cohort studies).31 In addition to demonstrating the active disease recurrence rates in this patient population, the trial also aims to identify risk factors for recurrent disease activity among treated MS patients.37 DISCO-MS builds upon a series of retrospective and observational studies that partially answered these questions, albeit in the context of biases inherent in retrospective or observational studies.
A Minneapolis MS Treatment and Research Center single-center study identified 77 SPMS patients with no acute CNS inflammatory events over 2 to 20 years and advised these patients to stop taking DMT.32 In this group, 11.7% of subjects experienced recurrent active disease. Age was the primary discriminating factor. The mean age of those who experienced disease activity was 56 years vs 61 years those who did not. A second observational study from France found that among 100 SPMS patients treated either with interferon β or glatiramer acetate for at least 6 months, 35% experienced some form of inflammatory disease upon discontinuation.38 Sixteen patients relapsed and 19 developed gadolinium-enhancing MR lesions after DMT discontinuation. However, the age of the cohort was younger than the Minneapolis study (47.2 years vs 61 years), and reasons for discontinuation (eg, AEs or lack of disease activity) were not considered in the analysis.
Other studies examining the safety of DMT discontinuation have not considered MS subtype or excluded patients with progressive subtypes of MS. The largest studies to date on DMT discontinuation utilized the international MSBase global patient registry, which identified nearly 5,000 patients who discontinued interferons (73%), glatiramer acetate (18%), natalizumab (6%), or fingolimod (3%), without specifying the reasons for discontinuation.39 Despite these shortcomings, data reveal trends that are helpful in predicting how MS tends to behave in patients who have discontinued therapy. Not surprisingly, disability progression was most likely among patients already characterized as having a progressive phenotype, while relapses were less likely to occur among older, progressive patients.
Although clinicians may be increasingly willing to discuss DMT discontinuation with their patients, at least 1 study exploring patient perspectives on stopping treatment suggests widespread reluctance to stop treatment. A survey conducted with participants in the North American Research Committee on Multiple Sclerosis patient-report registry found that among survey respondents, only 11.9% would discontinue their MS medication if deemed stable, while 66.3% stated they were unlikely to stop treatment.40
These results suggest that before clinicians incorporate DMT discontinuation into the normal course of discussion with patients, they should be prepared to provide both education (on the wisdom of stopping under the right circumstances) and evidence to support when and how to make the recommendation. Based on existing evidence, criteria for recommending treatment discontinuation might include prolonged freedom from disease activity (≥ 5 years), age > 55 years or 60 years, and a progressive disease course. Thus far, no combination of factors has been shown to completely predict an event-free transition off of medicine. Since no fixed algorithm yet exists to guide DMT stoppage in MS, reasonable suggestions for monitoring patients might include surveillance MRIs, more frequent clinic visits, and possible transitional treatment for patients coming off of natalizumab or fingolimod, since these drugs have been associated with rebound disease activity when discontinued.41,42
Clinicians wishing to maximize function and quality of life for their patients at any age or stage of disease should look to nonpharmacologic interventions to lessen disability and maximize quality of life. While beyond the scope of this discussion, preliminary evidence suggests multimodal (aerobic, resistance, balance) exercise may enhance endurance and cognitive processing speed, and that treatment of comorbid diseases affecting vascular health benefits MS. 43
