High-Risk PML Patients Switching from Natalizumab to Alemtuzumab: an Observational Study

A safety review of current monoclonal antibodies used to treat multiple sclerosis

INTRODUCTION

Multiple sclerosis (MS) is an autoimmune disease affecting the central nervous system. Monoclonal antibodies (mAbs) have shown efficacy in reducing MS relapse rates, disease progression, and brain lesion activity.

AREAS COVERED

This article reviews the literature on the use of mAbs for the treatment of MS, including their mechanisms of action, clinical trial data, safety profiles, and long-term outcomes. The review focuses on the three main categories of mAbs used in MS: alemtuzumab, natalizumab, and anti-CD20 drugs. A literature search was conducted using relevant keywords and guidelines and reports from regulatory agencies were reviewed. The search covered studies published from inception to 31 December 202231 December 2022. The article also discusses the potential risks and benefits of these therapies, including their effects on infection rates, malignancies, and vaccination efficacy.

EXPERT OPINION

Monoclonal antibodies have revolutionized the treatment of MS, but safety concerns must be considered, particularly with regards to infection rates, malignancy risk, and vaccination efficacy. Clinicians must weigh the potential benefits and risks of mAbs on an individual patient basis, taking into account factors such as age, disease severity, and comorbidities. Ongoing monitoring and surveillance are essential to ensure the long-term safety and effectiveness of monoclonal antibody therapies in MS.

Consensus statement on the use of alemtuzumab in daily clinical practice in Spain

INTRODUCTION

Alemtuzumab is a highly effective drug approved by the European Medicines Agency as a disease-modifying drug for the treatment of relapsing-remitting multiple sclerosis.

OBJECTIVE

A consensus document was drafted on the management of alemtuzumab in routine clinical practice in Spain.

DEVELOPMENT

A group of multiple sclerosis specialists reviewed articles addressing treatment with alemtuzumab in patients with multiple sclerosis and published before December 2017. The included studies assessed the drug's efficacy, effectiveness, and safety; screening for infections and vaccination; and administration and monitoring aspects. The initial proposed recommendations were developed by a coordinating group and based on the available evidence and their clinical experience. The consensus process was carried out in 2 stages, with the initial threshold percentage for group agreement established at 80%. The final document with all the recommendations agreed by the working group was submitted for external review and the comments received were considered by the coordinating group.

CONCLUSION

The present document is intended to be used as a tool for optimising the management of alemtuzumab in routine clinical practice.

Product review on MAbs (alemtuzumab and ocrelizumab) for the treatment of multiple sclerosis

Traditionally, the management of active relapsing remitting MS was based on the, so-called, maintenance therapy, which is characterized by continuous treatment with particular disease modifying therapy (DMT), and a return of disease activity when the drug is discontinued. Another approach is characterized by a short treatment course of a DMT, which is hypothesized to act as an immune reconstitution therapy (IRT), with the potential to protect against relapses for years after a short course of treatment. Introduction of monoclonal antibodies in the treatment of MS has revolutionized MS treatment in the last decade. However, given the increasingly complex landscape of DMTs approved for MS, people with MS and neurologists are constantly faced with the question which DMT is the most appropriate for the given patient, a question we still do not have an answer to. In this product review, we will discuss the first DMT that acts as IRT, an anti-CD52 monoclonal antibody alemtuzumab and an anti CD20 monoclonal antibody, ocrelizumab that has the potential to act as an IRT, but is administered continuously. Special emphasis will be given on safety in the context of COVID-19 pandemics and vaccination strategies.

How to switch disease-modifying treatments in multiple sclerosis: Guidelines from the French Multiple Sclerosis Society (SFSEP)

BACKGROUND

Today, there are no recommendations on switching disease-modifying treatments (DMTs) in multiple sclerosis (MS).

OBJECTIVES

To establish guidelines on switching DMTs MS.

METHODS

A Steering Committee composed of seven MS experts from the French Group for Recommendations in Multiple Sclerosis (France4MS) defined 15 proposals. These proposals were then submitted to a Rating Group, composed of 48 French MS experts, for evaluation. The proposals were classified as 'appropriate', 'inappropriate' or 'uncertain'.

RESULTS

Switching from a first-line therapy to another first-line therapy or a second-line therapy could be done without a washout period. Switching from a second-line therapy to a first-line therapy could be done without a washout period with fingolimod or natalizumab, after 3 months with ocrelizumab or mitoxantrone, and, if disease activity occurs with alemtuzumab or cladribine. The switch from a second-line therapy to another second-line therapy could be done after a washout period of 1 month with fingolimod or natalizumab, after 3 months with ocrelizumab, after 6 months with mitoxantrone, and, if disease activity occurs, with alemtuzumab or cladribine.

CONCLUSION

This expert consensus approach provides physicians with some guidelines on optimizing the benefit/risk ratio when switching DMTs in patients with MS.

Effect of switching from natalizumab to moderate- vs high-efficacy DMT in clinical practice

Objective

To assess the real-world comparative effectiveness of switching from natalizumab (NTZ) to a moderate-efficacy (Mod) disease-modifying therapy (DMT) vs high-efficacy therapy (HET) in patients with multiple sclerosis (MS).

Methods

Patients discontinuing NTZ at two MS centers (n = 556) who switched to Mod DMT (n = 270) vs HET (n = 130) were assessed using propensity score (PS) weighting. PS model covariates included demographics and baseline clinical and MRI characteristics. All outcomes were reported as Mod DMT vs HET.

Results

Of the patients included in the study, 48.6% switched to Mod DMT (dimethyl fumarate, n = 130; fingolimod, n = 140) vs 23.4% who switched to HET (ocrelizumab, n = 106; rituximab, n = 17; alemtuzumab, n = 7). Within the first 6 months post-NTZ, switchers to Mod DMT experienced comparable relapses (odds ratio [OR] = 1.36, 95% confidence interval [CI] [0.72-1.66], p = 0.724), although they had increased MRI activity on treatment (OR = 2.59, 95% CI [1.09-3.57], p = 0.037). By 24 months post-NTZ, there was no difference in the annualized relapse rate (OR = 1.44, 95% CI [0.69-1.59], p = 0.334) or time to first clinical relapse (HR = 2.12, 95% CI [0.87-5.17], p = 0.090), although switchers to Mod DMT had higher gadolinium-enhancing (GdE) lesions (OR = 3.62, 95% CI [1.56-5.21], p = 0.005), earlier time to first GdE lesion (HR = 6.67, 95% CI [2.06-9.16], p = 0.002), lower proportion with the absence of disease activity (OR = 0.41, 95% CI [0.21-0.71], p = 0.004), and higher risk of disability progression on T25FW (OR = 1.83, 95% CI [1.06-3.02], p = 0.043) and 9-HPT (OR = 1.81, 95% CI [1.05-3.56], p = 0.044).

Conclusion

Patients switching from NTZ to Mod DMT vs HET were at relatively increased risk of disease activity within the first 6 months of NTZ withdrawal that was sustained at 24 months, yielding greater disability progression.

[Monoclonal antibody therapies for rapidly progressive and highly active multiple sclerosis in the era of the COVID-19 pandemic]

As the COVID-19 pandemic continues, reducing the risk of infection for immunocompromised patients remains an important issue. Patients with aggressive multiple sclerosis (MS) require immunosuppressive therapy in order to control the overactive autoimmune response. Preliminary international and national trials demonstrate that older age, higher disability status and progressive MS are generally associated with a more severe clinical course of COVID-19. However, uncertainty remains about the effect of disease-modifying therapies on the COVID-19 clinical presentation. In this article, we pay special attention to monoclonal antibodies used for immune reconstitution therapy, which results in significant changes to the T-cell and/or B-cell repertoire. Based on the published data from registries in different countries, we attempted to estimate the benefits and risks of these therapies in a complicated epidemiological setting.

Newly approved agents for relapsing remitting multiple sclerosis: how real-world evidence compares with randomized clinical trials?

INTRODUCTION

In recent years, many treatment options have become available for relapsing remitting MS. Randomized clinical trials and real-world studies are complementary sources of information, and together have the potential to offer a comprehensive understanding of the safety and efficacy profiles of each drug, a critical factor for a personalized management of the disease.

AREAS COVERED

In this review, the authors provide an up-to-date review of both RCTs and real-world studies assessing the safety and efficacy profiles of recently developed disease-modifying drugs for relapsing remitting MS. These include fingolimod, teriflunomide, dimethyl fumarate, alemtuzumab and ocrelizumab.

EXPERT OPINION

From the authors' review of the literature, the efficacy profiles resulted from RCTs were confirmed by observational studies with regard to the disease-modifying drugs considered. The magnitude of the effects on annualized relapse rates and MRI active lesions was generally even larger in the observational studies compared to RCTs. From the safety point of view, observational studies revealed new adverse events, mostly in the area of bacterial and opportunistic infections, not seen in the relative registration programme. This is a very important gain because it allows to elaborate appropriate strategies to prevent and handle the risks.

The use of alemtuzumab in patients with relapsing-remitting multiple sclerosis: the Gulf perspective

Over the past decade, the development of high-efficacy disease-modifying therapies (DMTs) has been responsible for more effective management of relapsing-remitting multiple sclerosis (RRMS). However, the gaps in optimal care for this complex disease remain. Alemtuzumab (Lemtrada®) is a highly efficacious DMT that shows better patient outcomes and therapeutic benefits, but its use is under-recognized in the Gulf region. Experts in the care of multiple sclerosis shared their opinions based on study data and daily clinical experience in identifying the appropriate patient profile suitable for alemtuzumab's therapeutic benefits. Age, disease activity and severity, disability status, physician experience, and economic condition are some of the key indicators for alemtuzumab use.

Harmonization of real-world studies in multiple sclerosis: Retrospective analysis from the rirems group

BACKGROUND

Worldwide multiple sclerosis (MS) centers have coordinated their efforts to use data acquired in clinical practice for real-world observational studies. In this retrospective study, we aim to harmonize outcome measures, and to evaluate their heterogeneity within the Rising Italian Researchers in MS (RIReMS) study group.

METHODS

RIReMS members filled in a structured questionnaire evaluating the use of different outcome measures in clinical practice. Thereafter, thirty-four already-published papers from RIReMS centers were used for heterogeneity analyses, using the DerSimonian and Laird random-effects method to compute the between-study variance (τ²).

RESULTS

Based on questionnaire results, we defined basic modules for diagnosis and follow-up, consisting of outcome measures recorded by all participating centers at the time of diagnosis, and, then, at least annually; we also defined more detailed/optional modules, with outcome measures recorded less frequently and/or in the presence of specific clinical indications. Looking at heterogeneity, we found 5-year variance in age at onset (ES=27.34; 95%CI=26.18, 28.49; p<0.01; τ²=4.76), and 7% in female percent (ES=66.42; 95%CI=63.08, 69.76; p<0.01; τ²=7.15). EDSS variance was 0.2 in studies including patients with average age <36.1 years (ES=1.96; 95%CI=1.69, 2.24; p<0.01; τ²=0.19), or from 36.8 to 41.1 years (ES=2.70; 95%CI=2.39, 3.01; p<0.01; τ²=0.18), but increased to 3 in studies including patients aged >41.4 years (ES=4.37; 95%CI=3.40, 5.35; p<0.01; τ²=2.96). The lowest variance of relapse rate was found in studies with follow-up duration ≤2 years (ES=9.07; 95%CI=5.21, 12.93; p = 0.02; τ²=5.53), whilst the lowest variance in EDSS progression was found in studies with follow-up duration >2 years (ES=5.41; 95%CI=3.22, 7.60; p = 0.02; τ²=1.00).

DISCUSSION

We suggest common sets of biomarkers to be acquired in clinical practice, that can be used for research purposes. Also, we provide researchers with specific indications for improving inclusion criteria and data analysis, ultimately allowing data harmonization and high-quality collaborative studies.

Clinical outcomes in patients who discontinue natalizumab therapy after 2 years in the Tysabri® Observational Program (TOP)

BACKGROUND

Natalizumab is a highly efficacious therapy for relapsing-remitting multiple sclerosis (RRMS). Patients who discontinue natalizumab may experience return of MS disease activity.

OBJECTIVE

The aim of this study was to analyze predictors of post-natalizumab disease activity return.

METHODS

The Tysabri^® Observational Program (TOP) is an ongoing observational study of natalizumab-treated RRMS patients. Patients discontinuing natalizumab are encouraged to remain in TOP.

RESULTS

Analyses included 3221 TOP patients. After ⩾2 years on natalizumab, relapse risk was twice as high for patients who switched to an oral therapy (n = 660, hazard ratio (HR) = 2.18, p < 0.001) and three times as high for patients who switched to an injectable therapy (n = 95, HR = 3.02, p < 0.001) as for those who stayed on natalizumab (n = 2466). Relapse rates after switching remained below pre-natalizumab rates. In patients who switched to an oral therapy, higher relapse risk was predicted by longer washout time, more pre-natalizumab relapses, higher Expanded Disability Status Scale score at natalizumab initiation, and shorter natalizumab treatment duration.

CONCLUSION

Patients who stayed on natalizumab had better clinical outcomes than those who switched to an oral or injectable therapy after ⩾2 years on natalizumab. These results highlight modifiable risk factors for disease activity return (e.g. natalizumab treatment duration and washout duration) to consider when making treatment decisions.

Monoclonal Antibody Therapies for Multiple Sclerosis and Neuromyelitis Optica Spectrum Disorder

Considerable progress has been made in treatments for multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) over the last several decades. However, the present treatments do not show satisfactory efficacy or safety in a considerable proportion of patients, who experience relapse or disability progression despite receiving treatment and suffer from side effects, which can be severe. Improvements in the understanding of the pathophysiologies of MS and NMOSD have led to numerous therapeutic approaches being proposed and developed. Monoclonal antibodies (mAbs) are receiving increasing attention because of their specificity of action and likelihood of high efficacy with fewer side effects. Many mAbs have been evaluated, and some have been approved for MS or NMOSD treatment. This article reviews the use of mAbs for treating MS and NMOSD, including summarizing their mechanisms of action, efficacy, and safety profiles.

Alemtuzumab treatment of multiple sclerosis in real-world clinical practice: A report from a single Italian center

BACKGROUND

Alemtuzumab, is a compound approved for highly active MS, and, in Europe, employed after the use of other disease-modifying treatments (DMTs) with an escalation approach or used as a first therapeutic option. The occurrence of secondary autoimmune adverse events and or infections can differ depending on the employed approach.

OBJECTIVE

To evaluate the efficacy and safety of alemtuzumab in real-world MS population that encompassed patients previously treated with other DMTs.

METHODS

35 patients, treated with alemtuzumab in a single MS Center, were followed for at least 36 months. The study investigated the prevalence of patients reaching the phase of the non-active disease (NEDA-3). All the adverse events were also reported, and correlations assessed.

RESULTS

At the 36-month follow-up, 66,7% of patients achieved the NEDA-3 status, 90,5% of the patients were relapse-free, 85,7% showed no signs of disability progression, nor signs of MRI activity. Adverse events were observed in 45,7% of the patients and ranked as severe in 23% of them. Cases of autoimmune hemolytic anemia (AIHA), pancytopenia, viral hepatitis E, and noninfectious meningo-encephalomyelitis were found and reported. For these complications, the post hoc analysis showed possible interactive factors and causality related to previous DMT treatments.

CONCLUSIONS

In a real-world MS population like the one investigated in our study, alemtuzumab was found to be an effective treatment when employed as an escalation or rescue therapy. The compound exhibits a variable safety profile and frequent adverse events that are likely depending on previous treatments and their impact on the immune system.

Post-natalizumab disease reactivation in multiple sclerosis: systematic review and meta-analysis

Background

Natalizumab (NTZ) is sometimes discontinued in patients with multiple sclerosis, mainly due to concerns about the risk of progressive multifocal leukoencephalopathy. However, NTZ interruption may result in recrudescence of disease activity.

Objective

The objective of this study was to summarize the available evidence about NTZ discontinuation and to identify which patients will experience post-NTZ disease reactivation through meta-analysis of existing literature data.

Methods

PubMed was searched for articles reporting the effects of NTZ withdrawal in adult patients (⩾18 years) with relapsing-remitting multiple sclerosis (RRMS). Definition of disease activity following NTZ discontinuation, proportion of patients who experienced post-NTZ disease reactivation, and timing to NTZ discontinuation to disease reactivation were systematically reviewed. A generic inverse variance with random effect was used to calculate the weighted effect of patients' clinical characteristics on the risk of post-NTZ disease reactivation, defined as the occurrence of at least one relapse.

Results

The original search identified 205 publications. Thirty-five articles were included in the systematic review. We found a high level of heterogeneity across studies in terms of sample size (10 to 1866 patients), baseline patient characteristics, follow up (1-24 months), outcome measures (clinical and/or radiological), and definition of post-NTZ disease reactivation or rebound. Clinical relapses were observed in 9-80% of patients and peaked at 4-7 months, whereas radiological disease activity was observed in 7-87% of patients starting at 6 weeks following NTZ discontinuation. The meta-analysis of six articles, yielding a total of 1183 patients, revealed that younger age, higher number of relapses and gadolinium-enhanced lesions before treatment start, and fewer NTZ infusions were associated with increased risk for post-NTZ disease reactivation (p ⩽ 0.05).

Conclusions

Results from the present review and meta-analysis can help to profile patients who are at greater risk of post-NTZ disease reactivation. However, potential reporting bias and variability in selected studies should be taken into account when interpreting our data.

Post-natalizumab disease reactivation in multiple sclerosis: systematic review and meta-analysis

Background:

Natalizumab (NTZ) is sometimes discontinued in patients with multiple sclerosis, mainly due to concerns about the risk of progressive multifocal leukoencephalopathy. However, NTZ interruption may result in recrudescence of disease activity.

Objective:

The objective of this study was to summarize the available evidence about NTZ discontinuation and to identify which patients will experience post-NTZ disease reactivation through meta-analysis of existing literature data.

Methods:

PubMed was searched for articles reporting the effects of NTZ withdrawal in adult patients (⩾18 years) with relapsing–remitting multiple sclerosis (RRMS). Definition of disease activity following NTZ discontinuation, proportion of patients who experienced post-NTZ disease reactivation, and timing to NTZ discontinuation to disease reactivation were systematically reviewed. A generic inverse variance with random effect was used to calculate the weighted effect of patients’ clinical characteristics on the risk of post-NTZ disease reactivation, defined as the occurrence of at least one relapse.

Results:

The original search identified 205 publications. Thirty-five articles were included in the systematic review. We found a high level of heterogeneity across studies in terms of sample size (10 to 1866 patients), baseline patient characteristics, follow up (1–24 months), outcome measures (clinical and/or radiological), and definition of post-NTZ disease reactivation or rebound. Clinical relapses were observed in 9–80% of patients and peaked at 4–7 months, whereas radiological disease activity was observed in 7–87% of patients starting at 6 weeks following NTZ discontinuation. The meta-analysis of six articles, yielding a total of 1183 patients, revealed that younger age, higher number of relapses and gadolinium-enhanced lesions before treatment start, and fewer NTZ infusions were associated with increased risk for post-NTZ disease reactivation (p ⩽ 0.05).

Conclusions:

Results from the present review and meta-analysis can help to profile patients who are at greater risk of post-NTZ disease reactivation. However, potential reporting bias and variability in selected studies should be taken into account when interpreting our data.

Alemtuzumab as rescue therapy in case of multiple sclerosis rebound following Natalizumab break: Clinical case and literature review

INTRODUCTION

Natalizumab break exposes multiple sclerosis (MS) patients to a high risk of disease reactivation or rebound, whose prevention and treatment constitute a clinical challenge.

CASE PRESENTATION

We describe a dramatic case of MS rebound, characterized by the development of severe neurological and psychiatric symptoms, following natalizumab break. Alemtuzumab rapidly and completely suppressed brain inflammation as demonstrated by clinical and radiological findings.

CONCLUSIONS

Our case further adds to the available literature evidence on Alemtuzumab as first-choice rescue therapy following Natalizumab discontinuation.

Managing the side effects of multiple sclerosis therapy: pharmacotherapy options for patients

INTRODUCTION

Multiple sclerosis (MS) is an immune-mediated and neurodegenerative disease with an unpredictable outcome. Immune-modulatory treatment aims at decreasing long-term disability. With the increasing number of treatment options, it is essential to fully digest the possible side effects of the available therapeutics and to monitor patients is essential.

AREAS COVERED

All approved disease-modifying drugs (DMD) for MS are discussed in this review. Mode of action, adverse effects, reported risks for infections and malignancies, and pregnancy related issues are discussed in the review. The authors also provide suggestions for monitoring therapy. For all approved DMDs the pivotal studies have been included for possible side effects, as well as reports by health authorities. For this manuscript, PubMed was checked for reports on side effects for various drugs.

EXPERT OPINION

Treatment options in MS are manifold, each carrying different risks. The safety-risk profile for approved agents is favorable. Knowing and monitoring these possible side effects is essential to minimize risks associated with treatment. Presently, the long-term experience for some of these therapies is missing and this must be addressed.

The sequence of disease-modifying therapies in relapsing multiple sclerosis: safety and immunologic considerations

The treatment landscape for relapsing forms of multiple sclerosis (RMS) has expanded considerably over the last 10 years with the approval of multiple new disease-modifying therapies (DMTs), and others in late-stage clinical development. All DMTs for RMS are believed to reduce central nervous system immune-mediated inflammatory processes, which translate into demonstrable improvement in clinical and radiologic outcomes. However, some DMTs are associated with long-lasting effects on the immune system and/or serious adverse events, both of which may complicate the use of subsequent therapies. When customizing a treatment program, a benefit–risk assessment must consider multiple factors, including the efficacy of the DMT to reduce disease activity, the short- and long-term safety and immunologic profiles of each DMT, the criteria used to define switching treatment, and the risk tolerance of each patient. A comprehensive benefit–risk assessment can only be achieved by evaluating the immunologic, safety, and efficacy data for DMTs in the controlled clinical trial environment and the postmarketing clinical practice setting. This review is intended to help neurologists make informed decisions when treating RMS by summarizing the known data for each DMT and raising awareness of the multiple considerations involved in treating people with RMS throughout the entire course of their disease.

Alemtuzumab in the long-term treatment of relapsing-remitting multiple sclerosis: an update on the clinical trial evidence and data from the real world

Alemtuzumab is a humanized monoclonal antibody approved for the treatment of relapsing-remitting multiple sclerosis (RRMS), given as two annual courses on five consecutive days at baseline and on three consecutive days 12 months later. Here we provide an update on the long-term efficacy and safety of alemtuzumab in RRMS, including real-world experience, and advances in our understanding of its mechanism of action. Recent data from the phase II/III extension study have demonstrated that alemtuzumab reduces relapse rates, disability worsening, and the rate of brain volume loss over the long term, with many patients achieving no evidence of disease activity. In high proportions of patients, preexisting disability remained stable or improved. Alemtuzumab is associated with a consistent safety profile over the long term, with no new safety signals emerging and the overall annual incidence of reported adverse events decreasing after the first year on treatment. Acyclovir prophylaxis reduces herpetic infections, and monitoring has been shown to mitigate the risk of autoimmune adverse events, allowing early detection and overall effective management. Data from clinical practice and ongoing observational studies are providing additional information on the real-world use of alemtuzumab. Recent evidence on the mechanism of action of alemtuzumab indicates that in addition to its previously known effects of inducing depletion and repopulation of T and B lymphocytes, it also results in a relative increase of cells with memory and regulatory phenotypes and a decrease in cells with a proinflammatory signature, and may further promote an immunoregulatory environment through an impact on other innate immune cells (e.g. dendritic cells) that play a role in MS. These effects may allow preservation of innate immunity and immunosurveillance. Together, these lines of evidence help explain the durable clinical efficacy of alemtuzumab, in the absence of continuous treatment, in patients with RRMS.

Natalizumab in Multiple Sclerosis: Long-Term Management

Natalizumab is a monoclonal antibody highly effective in the treatment of relapsing remitting multiple sclerosis (RRMS) patients. Despite its effectiveness, there are growing concerns regarding the risk of progressive multifocal leukoencephalopathy (PML), a brain infection caused by John Cunningham virus (JCV), particularly after 24 doses and in patients who previously received immunosuppressive drugs. Long-term natalizumab treated, immunosuppressive-pretreated, and JCV antibody-positive patients are asked to rediscuss natalizumab continuation or withdrawal after 24 doses. Until now, there has not been a clear strategy that should be followed to avoid PML risk and in parallel reduce clinical and radiological rebound activity. In this review, we analyzed the results of clinical trials and case reports in relation to the following situations: natalizumab continuation, natalizumab discontinuation followed by full therapeutic suspension or switch to other first or second line MS treatments. Quitting all MS treatment after natalizumab increases MS activity occurrence. The results regarding the therapeutic switch are not homogeneous, so at the moment there are no established guidelines regarding natalizumab treatment after 24 administrations; the choice is currently based on the professional experience of the neurologist, and on patients' clinical features and preferences.