Using instrumental variables to correct for bias in real-world cohort studies of the effects of disease-modifying treatment in MS.

BACKGROUND: Estimating the effect of disease-modifying treatment of MS in observational studies is impaired by bias from unmeasured confounders, in particular indication bias. OBJECTIVE: To show how instrumental variables (IVs) reduce bias. METHODS: All patients with relapsing onset of MS 1996-2010, identified by the nationwide Danish Multiple Sclerosis Registry, were followed from onset. Exposure was treatment index throughout the first 12 years from onset, defined as a cumulative function of months without and with medium- or high-efficacy treatment, and outcomes were hazard ratios (HRs) per unit treatment index for sustained Expanded Disability Scale Score (EDSS) 4 and 6 adjusted for age at onset and sex, without and with an IV. We used the onset cohort (1996-2000; 2001-2005; 2006-2010) as an IV because treatment index increased across the cohorts. RESULTS: We included 6014 patients. With conventional Cox regression, HRs for EDSS 4 and 6 were 1.15 [95% CI: 1.13-1.18] and 1.17 [1.13-1.20] per unit treatment index. Only with IVs, we confirmed a beneficial effect of treatment with HRs of 0.86 [0.81-0.91] and 0.82 [0.74-0.90]. CONCLUSION: The use of IVs eliminates indication bias and confirms that treatment is effective in delaying disability. IVs could, under some circumstances, be an alternative to marginal structural models.

Torben Fog - A Danish pioneer in a multi-faceted spectrum of multiple sclerosis research.

Torben Fog was committed to multiple sclerosis (MS) research for more than four decades, starting before the defence of his thesis in 1948 and lasting until his death in 1987. His research was multi-facetted, making him one of the great pioneers in the study of essential parts of the pathology, immunology and treatment of MS. He has contributed with meticulous studies of the MS plaques, documenting the perivenous distribution of plaques in the spinal cord. He constructed a scoring system for the disability in MS and used a computer programme to calculate a total neurological deficit. Together with his co-workers, Fog in 1972 was the first to report the association between MS and the human leukocyte antigen system. Fog can be considered as the father of immunomodulatory therapy in MS, treating MS patients with the first transfer factor, and as early as 1980, he was the first to treat MS with intramuscular natural interferon.

A wearable device perspective on the standard definitions of disability progression in multiple sclerosis.

INTRODUCTION: Multiple sclerosis (MS) is a leading cause of disability among young adults, but standard clinical scales may not accurately detect subtle changes in disability occurring between visits. This study aims to explore whether wearable device data provides more granular and objective measures of disability progression in MS. METHODS: Remote Assessment of Disease and Relapse in Central Nervous System Disorders (RADAR-CNS) is a longitudinal multicenter observational study in which 400 MS patients have been recruited since June 2018 and prospectively followed up for 24 months. Monitoring of patients included standard clinical visits with assessment of disability through use of the Expanded Disability Status Scale (EDSS), 6-minute walking test (6MWT) and timed 25-foot walk (T25FW), as well as remote monitoring through the use of a Fitbit. RESULTS: Among the 306 patients who completed the study (mean age, 45.6 years; females 67%), confirmed disability progression defined by the EDSS was observed in 74 patients, who had approximately 1392 fewer daily steps than patients without disability progression. However, the decrease in the number of steps experienced over time by patients with EDSS progression and stable patients was not significantly different. Similar results were obtained with disability progression defined by the 6MWT and the T25FW. CONCLUSION: The use of continuous activity monitoring holds great promise as a sensitive and ecologically valid measure of disability progression in MS.

Early history of the European Journal of Neurology. A mirror of the evolution of Europe after 1989.

This paper retraces the early history of the European Journal of Neurology (EJN), as it is about to enter its 30th year. It describes how our discipline organized itself during the latter part of the 20th century in Europe. In some ways, the creation and the evolution of the journal parallel the process of unification of Europe in its current form in the late 1980s and early 1990s. It started as a new journal with no impact factor and no indexation. It grew progressively thanks to the support of the European Federation of Neurological Societies (EFNS) and from the European scientific community The progressive merging of EFNS with the European Society of Neurology and the creation of the European Academy of Neurology were essential for reaching the current prominence of EJN within neurological publishing and for making it the widely heard official voice of European neurology.

Heterogeneity on long-term disability trajectories in patients with secondary progressive MS: a latent class analysis from Big MS Data network.

BACKGROUND: Over the decades, several natural history studies on patients with primary (PPMS) or secondary progressive multiple sclerosis (SPMS) were reported from international registries. In PPMS, a consistent heterogeneity on long-term disability trajectories was demonstrated. The aim of this study was to identify subgroups of patients with SPMS with similar longitudinal trajectories of disability over time. METHODS: All patients with MS collected within Big MS registries who received an SPMS diagnosis from physicians (cohort 1) or satisfied the Lorscheider criteria (cohort 2) were considered. Longitudinal Expanded Disability Status Scale (EDSS) scores were modelled by a latent class growth analysis (LCGA), using a non-linear function of time from the first EDSS visit in the range 3-4. RESULTS: A total of 3613 patients with SPMS were included in the cohort 1. LCGA detected three different subgroups of patients with a mild (n=1297; 35.9%), a moderate (n=1936; 53.6%) and a severe (n=380; 10.5%) disability trajectory. Median time to EDSS 6 was 12.1, 5.0 and 1.7 years, for the three groups, respectively; the probability to reach EDSS 6 at 8 years was 14.4%, 78.4% and 98.3%, respectively. Similar results were found among 7613 patients satisfying the Lorscheider criteria. CONCLUSIONS: Contrary to previous interpretations, patients with SPMS progress at greatly different rates. Our identification of distinct trajectories can guide better patient selection in future phase 3 SPMS clinical trials. Additionally, distinct trajectories could reflect heterogeneous pathological mechanisms of progression.

The peripheral endocannabinoid system and its association with biomarkers of inflammation in untreated patients with multiple sclerosis.

BACKGROUND AND PURPOSE: The endocannabinoid system (ECS) has been found altered in patients with multiple sclerosis (MS). However, whether the ECS alteration is present in the early stage of MS remains unknown. First, we aimed to compare the ECS profile between newly diagnosed MS patients and healthy controls (HCs). Next, we explored the association of the ECS, biomarkers of inflammation, and clinical parameters in newly diagnosed MS patients. METHODS: Whole blood gene expression of ECS components and levels of endocannabinoids in plasma were measured by real-time quantitative polymerase chain reaction and ultra-high-pressure liquid chromatography-mass spectrometry, respectively, in 66 untreated MS patients and 46 HCs. RESULTS: No differences were found in the gene expression or plasma levels of the selected ECS components between newly diagnosed MS patients and HCs. Interferon-γ, encoded by the gene IFNG, correlated positively (ρ = 0.60) with the expression of G protein-coupled receptor 55 (GPR55), and interleukin1ß (IL1B) correlated negatively (ρ = -0.50) with cannabinoid receptor 2 (CNR2) in HCs. CONCLUSIONS: We found no alteration in the peripheral ECS between untreated patients with MS and HC. Furthermore, our results indicate that the ECS has a minor overall involvement in the early stage of MS on inflammatory markers and clinical parameters when compared with HCs.

Short-Term versus Long-Term Mentalization-Based Therapy for Borderline Personality Disorder: A Randomized Clinical Trial (MBT-RCT).

INTRODUCTION: Borderline personality disorder (BPD) is a severe and prevalent psychiatric disorder. Mentalization-based therapy (MBT) is an evidence-based intervention for BPD, and several countries offer treatment programs for BPD lasting for years, which is resource demanding. No previous trial has compared short-term with long-term MBT. OBJECTIVE: The aim of the study was to assess the efficacy and safety of short-term versus long-term MBT for outpatients with BPD. METHODS: Adult outpatients (≥18 years) with subthreshold or diagnosed BPD were randomly assigned (1:1) to short-term MBT (5 months) or long-term MBT (14 months). The primary outcome was BPD symptoms assessed with the Zanarini Rating Scale for Borderline Personality Disorder. Secondary outcomes were functional impairment, quality of life, global functioning, and severe self-harm. All outcomes were primarily assessed at 16 months after randomization. This trial was prospectively registered at ClinicalTrials.gov, NCT03677037. RESULTS: Between October 4, 2018, and December 3, 2020, we randomly assigned 166 participants to short-term MBT (n = 84) or long-term MBT (n = 82). Regression analyses showed no evidence of a difference when assessing BPD symptoms (MD 0.99; 95% CI: -1.06 to 3.03; p = 0.341), level of functioning (MD 1.44; 95% CI: -1.43 to 4.32; p = 0.321), quality of life (MD -0.91; 95% CI: -4.62 to 2.79; p = 0.626), global functioning (MD -2.25; 95% CI: -6.70 to 2.20; p = 0.318), or severe self-harm (RR 1.37; 95% CI: 0.70-2.84; p = 0.335). More participants in the long-term MBT group had a serious adverse event compared with short-term MBT (RR 1.63; 95% CI: 0.94-3.07; p = 0.088), primarily driven by a difference in psychiatric hospitalizations (RR 2.03; 95% CI: 0.99-5.09; p = 0.056). CONCLUSION: Long-term MBT did not lead to lower levels of BPD symptoms, nor did it influence any of the secondary outcomes compared with short-term MBT.

The difference between shorter- versus longer-term psychotherapy for adult mental health disorders: a systematic review with meta-analysis.

BACKGROUND: The optimal psychotherapy duration for mental health disorders is unclear. Our aim was to assess the beneficial and harmful effects of shorter- versus longer-term psychotherapy for adult mental health disorders. METHOD: We searched relevant databases and websites for published and unpublished randomised clinical trials assessing different durations of the same psychotherapy type before June 27, 2022. Our methodology was based on Cochrane and an eight-step procedure. Primary outcomes were quality of life, serious adverse events, and symptom severity. Secondary outcomes were suicide or suicide-attempts, self-harm, and level of functioning. RESULTS: We included 19 trials randomising 3,447 participants. All trials were at high risk of bias. Three single trials met the required information size needed to confirm or reject realistic intervention effects. One single trial showed no evidence of a difference between 6 versus 12 months dialectical behavioral therapy for borderline personality when assessing quality of life, symptom severity, and level of functioning. One single trial showed evidence of a beneficial effect of adding booster sessions to 8 and 12 weeks of internet-based cognitive behavioral therapy for depression and anxiety when assessing symptom severity and level of functioning. One single trial showed no evidence of a difference between 20 weeks versus 3 years of psychodynamic psychotherapy for mood- or anxiety disorders when assessing symptom severity and level of functioning. It was only possible to conduct two pre-planned meta-analyses. Meta-analysis showed no evidence of a difference between shorter- and longer-term cognitive behavioural therapy for anxiety disorders on anxiety symptoms at end of treatment (SMD: 0.08; 95% CI: -0.47 to 0.63; p = 0.77; I2 = 73%; four trials; very low certainty). Meta-analysis showed no evidence of a difference between shorter and longer-term psychodynamic psychotherapy for mood- and anxiety disorders on level of functioning (SMD 0.16; 95% CI -0.08 to 0.40; p = 0.20; I2 = 21%; two trials; very low certainty). CONCLUSIONS: The evidence for shorter versus longer-term psychotherapy for adult mental health disorders is currently unclear. We only identified 19 randomised clinical trials. More trials at low risk of bias and at low risk of random errors assessing participants at different levels of psychopathological severity are urgently needed. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42019128535.

Automatic Assessment of the 2-Minute Walk Distance for Remote Monitoring of People with Multiple Sclerosis.

The aim of this study was to investigate the feasibility of automatically assessing the 2-Minute Walk Distance (2MWD) for monitoring people with multiple sclerosis (pwMS). For 154 pwMS, MS-related clinical outcomes as well as the 2MWDs as evaluated by clinicians and derived from accelerometer data were collected from a total of 323 periodic clinical visits. Accelerometer data from a wearable device during 100 home-based 2MWD assessments were also acquired. The error in estimating the 2MWD was validated for walk tests performed at hospital, and then the correlation (r) between clinical outcomes and home-based 2MWD assessments was evaluated. Robust performance in estimating the 2MWD from the wearable device was obtained, yielding an error of less than 10% in about two-thirds of clinical visits. Correlation analysis showed that there is a strong association between the actual and the estimated 2MWD obtained either at hospital (r = 0.71) or at home (r = 0.58). Furthermore, the estimated 2MWD exhibits moderate-to-strong correlation with various MS-related clinical outcomes, including disability and fatigue severity scores. Automatic assessment of the 2MWD in pwMS is feasible with the usage of a consumer-friendly wearable device in clinical and non-clinical settings. Wearable devices can also enhance the assessment of MS-related clinical outcomes.

Cardiovascular Safety of Degarelix Versus Leuprolide in Patients With Prostate Cancer: The Primary Results of the PRONOUNCE Randomized Trial.

BACKGROUND: The relative cardiovascular safety of gonadotropin-releasing hormone (GnRH) antagonists compared with GnRH agonists in men with prostate cancer and known atherosclerotic cardiovascular disease remains controversial. METHODS: In this international, multicenter, prospective, randomized, open-label trial, men with prostate cancer and concomitant atherosclerotic cardiovascular disease were randomly assigned 1:1 to receive the GnRH antagonist degarelix or the GnRH agonist leuprolide for 12 months. The primary outcome was the time to first adjudicated major adverse cardiovascular event (composite of death, myocardial infarction, or stroke) through 12 months. RESULTS: Because of slower-than-projected enrollment and fewer-than-projected primary outcome events, enrollment was stopped before the 900 planned participants were accrued. From May 3, 2016, to April 16, 2020, a total of 545 patients from 113 sites across 12 countries were randomly selected. Baseline characteristics were balanced between study groups. The median age was 73 years, 49.8% had localized prostate cancer; 26.3% had locally advanced disease, and 20.4% had metastatic disease. A major adverse cardiovascular event occurred in 15 (5.5%) patients assigned to degarelix and 11 (4.1%) patients assigned to leuprolide (hazard ratio, 1.28 [95% CI, 0.59-2.79]; P=0.53). CONCLUSIONS: PRONOUNCE (A Trial Comparing Cardiovascular Safety of Degarelix Versus Leuprolide in Patients With Advanced Prostate Cancer and Cardiovascular Disease) is the first, international, randomized clinical trial to prospectively compare the cardiovascular safety of a GnRH antagonist and a GnRH agonist in patients with prostate cancer. The study was terminated prematurely because of the smaller than planned number of participants and events, and no difference in major adverse cardiovascular events at 1 year between patients assigned to degarelix or leuprolide was observed. The relative cardiovascular safety of GnRH antagonists and agonists remains unresolved. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02663908.

Role of B Cells in Multiple Sclerosis and Related Disorders.

The success of clinical trials of selective B-cell depletion in patients with relapsing multiple sclerosis (MS) and primary progressive MS has led to a conceptual shift in the understanding of MS pathogenesis, away from the classical model in which T cells were the sole central actors and toward a more complex paradigm with B cells having an essential role in both the inflammatory and neurodegenerative components of the disease process. The role of B cells in MS was selected as the topic of the 27th Annual Meeting of the European Charcot Foundation. Results of the meeting are presented in this concise review, which recaps current concepts underlying the biology and therapeutic rationale behind B-cell-directed therapeutics in MS, and proposes strategies to optimize the use of existing anti-B-cell treatments and provide future directions for research in this area. ANN NEUROL 2021;89:13-23.

The risk of infections for multiple sclerosis and neuromyelitis optica spectrum disorder disease-modifying treatments: Eighth European Committee for Treatment and Research in Multiple Sclerosis Focused Workshop Review. April 2021.

Over the recent years, the treatment of multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) has evolved very rapidly and a large number of disease-modifying treatments (DMTs) are now available. However, most DMTs are associated with adverse events, the most frequent of which being infections. Consideration of all DMT-associated risks facilitates development of risk mitigation strategies. An international focused workshop with expert-led discussions was sponsored by the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) and was held in April 2021 to review our current knowledge about the risk of infections associated with the use of DMTs for people with MS and NMOSD and corresponding risk mitigation strategies. The workshop addressed DMT-associated infections in specific populations, such as children and pregnant women with MS, or people with MS who have other comorbidities or live in regions with an exceptionally high infection burden. Finally, we reviewed the topic of DMT-associated infectious risks in the context of the current SARS-CoV-2 pandemic. Herein, we summarize available evidence and identify gaps in knowledge which justify further research.

Treating Avoidant Personality Disorder With Combined Individual Metacognitive Interpersonal Therapy and Group Mentalization-Based Treatment: A Pilot Study.

ABSTRACT: Avoidant personality disorder (AvPD) is a severe but understudied condition. The current pilot project reports data on acceptability and outcomes of a novel treatment combining biweekly individual metacognitive interpersonal therapy (MIT) and weekly mentalization-based therapy (MBT) group therapy. A total of 30 patients with AvPD were consecutively included in the program. The primary outcome was AvPD-specific personality functioning measured by self-report after treatment. Secondary outcomes were symptom distress, interpersonal problems, quality of life, and psychosocial functioning. Twenty-two patients completed treatment, with a mean duration of 13 months. On the primary outcome, effect sizes were generally moderate to large (effect size range: 0.59-1.10). On secondary outcomes, effect sizes were large (effect size range: 0.77-2.3). Both in terms of acceptability and outcomes, results are promising for the combination of MIT and MBT for AvPD. The approach is a strong candidate for further investigation in future large-scale randomized controlled trial.

Fitbeat: COVID-19 estimation based on wristband heart rate using a contrastive convolutional auto-encoder.

This study proposes a contrastive convolutional auto-encoder (contrastive CAE), a combined architecture of an auto-encoder and contrastive loss, to identify individuals with suspected COVID-19 infection using heart-rate data from participants with multiple sclerosis (MS) in the ongoing RADAR-CNS mHealth research project. Heart-rate data was remotely collected using a Fitbit wristband. COVID-19 infection was either confirmed through a positive swab test, or inferred through a self-reported set of recognised symptoms of the virus. The contrastive CAE outperforms a conventional convolutional neural network (CNN), a long short-term memory (LSTM) model, and a convolutional auto-encoder without contrastive loss (CAE). On a test set of 19 participants with MS with reported symptoms of COVID-19, each one paired with a participant with MS with no COVID-19 symptoms, the contrastive CAE achieves an unweighted average recall of 95.3 % , a sensitivity of 100 % and a specificity of 90.6 % , an area under the receiver operating characteristic curve (AUC-ROC) of 0.944, indicating a maximum successful detection of symptoms in the given heart rate measurement period, whilst at the same time keeping a low false alarm rate.

A clinical illustration of short-term mentalization-based therapy for borderline personality disorder.

OBJECTIVE: Mentalization-based therapy (MBT) is an evidence-supported, long-term psychotherapy program developed to treat borderline personality disorder (BPD). A short-term, 20-week adaptation to the original MBT format including case formulation, psychoeducation, and group and individual therapy has recently been proposed. The current case material will illustrate how the recent adaptation to the mentalization-based practice can enhance personality functioning using a short-term format. METHODS: Case material is presented to demonstrate the clinical application of short-term MBT in the treatment of a young woman diagnosed with BPD who has a history of failed treatment attempts and who showed signs of affective dysregulation, unstable relationships, and intense abandonment anxiety. RESULTS: The case illustration shows how short-term MBT can facilitate improvement in personality functioning, specifically targeting situations in which the patient lost her temper and became overwhelmed by abandonment anxiety. By continuously employing therapeutic shifts toward greater autonomy and agency, and by maintaining a balanced empathetic therapeutic stance, the therapists were able to enhance the patients mentalizing and personality functioning. CONCLUSIONS: Short-term MBT can be effectively implemented to enhance the mentalizing capacity and personality functioning in outpatients with BPD.

Highly effective disease-modifying treatment as initial MS therapy.

PURPOSE OF REVIEW: Using highly effective (HE) compounds right from the beginning of disease-modifying immunotherapy (DMT) in people with multiple sclerosis (pwMS) has gained popularity among clinicians and pwMS alike. We discuss the most recent evidence supporting this approach, and whether any of the associated risks should stop us adopting it as a default strategy. RECENT FINDINGS: With the addition of injectable ofatumumab, and the two oral sphingosine one phosphate modulators siponimod and ozanimod, ten HE DMTs are now available for pwMS, though variation in licensing status and cost may limit their use in some healthcare environments. Real World evidence based on large MS registry data suggests the superiority of early HE DMT over a slow treatment escalation approach; delaying HE DMT leads to more rapid and often irreversible disability accrual. Mechanistically, B-cell depletion, particularly memory B-cell suppression, is a common denominator closely associated with DMT efficacy. SUMMARY: The concept that HE DMTs are necessarily associated with a high risk of adverse effects, is no longer supported by the evidence. The rather predictable and manageable risk profile of most HE DMTs should lower the threshold for clinicians to discuss such treatment with pwMS as a first line approach.

Effect of lateral therapy switches to oral moderate-efficacy drugs in multiple sclerosis: a nationwide cohort study.

BACKGROUND: Switching between first-line disease-modifying therapies in patients with clinically stable relapsing-remitting multiple sclerosis (RRMS) due to reasons other than disease activity is frequent, but evidence on the effect of this practice is limited. We investigated the effect of switching patients with stable RRMS on occurrences of disability accumulation, relapses and future treatment discontinuation. METHODS: Using the Danish Multiple Sclerosis Registry, we identified patients with RRMS without disease activity who either (1) stayed on injectable platform therapy (interferon-ß or glatiramer acetate) or (2) switched to dimethyl fumarate (DMF) or teriflunomide (TFL) and compared treatment outcomes using propensity-score-based methods and marginal structural models (MSM). RESULTS: We included 3206 patients in the study. We found no change in risk of 6-month confirmed Expanded Disability Status Scale score worsening in patients switching to DMF (HR: 1.15, 95% CI 0.88 to 1.50) or TFL (HR: 1.16, 95% CI 0.92 to 1.46). The risk of suffering any relapse tended to decrease when switching to DMF (HR: 0.73, 95% CI 0.51 to 1.04) and tended to increase when switching to TFL (HR: 1.25, 95% CI 0.96 to 1.63). Absolute risk differences were small. MSM analyses showed similar results but did not find an increased relapse risk in TFL switchers. CONCLUSION: Switching from injectable platform therapies to oral first-line therapies in patients with clinically stable RRMS does not increase the risk of disability accumulation. While the postswitch risk of relapses trended towards marginally higher on TFL, this trend was eliminated by adjustment for time-variant confounders.

The introduction of new medications in pediatric multiple sclerosis: Open issues and challenges.

Disease-modifying drugs (DMDs) for multiple sclerosis (MS) have been evaluated in pediatric patients in observational studies demonstrating a similar, even better clinical effect compared to adults, with a similar safety. Only fingolimod has been tested in a randomized controlled trial (RCT) and is approved for pediatric multiple sclerosis (ped-MS). Numerous methodological, practical, and ethical issues underline that RCTs are difficult to conduct in ped-MS. This also creates a lack of safety information. To facilitate the availability of new agents in ped-MS, we encourage to develop a different approach based on pharmacokinetic/pharmacodynamic studies to yield information on optimal doses and implementation of obligatory registries to obtain information on safety as primary endpoint.

Early treatment delays long-term disability accrual in RRMS: Results from the BMSD network.

BACKGROUND: The optimal timing of treatment starts for achieving the best control on the long-term disability accumulation in multiple sclerosis (MS) is still to be defined. OBJECTIVE: The aim of this study was to estimate the optimal time to start disease-modifying therapies (DMTs) to prevent the long-term disability accumulation in MS, using a pooled dataset from the Big Multiple Sclerosis Data (BMSD) network. METHODS: Multivariable Cox regression models adjusted for the time to first treatment start from disease onset (in quintiles) were used. To mitigate the impact of potential biases, a set of pairwise propensity score (PS)-matched analyses were performed. The first quintile, including patients treated within 1.2 years from onset, was used as reference. RESULTS: A cohort of 11,871 patients (median follow-up after treatment start: 13.2 years) was analyzed. A 3- and 12-month confirmed disability worsening event and irreversible Expanded Disability Status Scale (EDSS) 4.0 and 6.0 scores were reached by 7062 (59.5%), 4138 (34.9%), 3209 (31.1%), and 1909 (16.5%) patients, respectively. The risk of reaching all the disability outcomes was significantly lower (p < 0.0004) for the first quintile patients' group. CONCLUSION: Real-world data from the BMSD demonstrate that DMTs should be commenced within 1.2 years from the disease onset to reduce the risk of disability accumulation over the long term.

Exposure to passive smoking during adolescence is associated with an increased risk of developing multiple sclerosis.

BACKGROUND: Environmental factors are associated with acquiring multiple sclerosis (MS) particularly in adolescence. OBJECTIVE: To test for association between MS and exposure to passive smoking at the age of 10-19. METHODS: A total of 919 patients from the Danish MS Registry and Biobank and 3419 healthy blood donors who had not smoked before the age of 19 were targeted. We analyzed separately for each sex and for those never-smokers (cohort 1) and active smokers above the age of 19 (cohort 2). All participants completed standardized questionnaires about smoking and lifestyle. We matched cases and controls in the ratio of 1:2 by propensity scores discarding unmatchable individuals and used logistic regression adjusted for all covariates and interactions. RESULTS: After matching, we included 110/213 male cases/controls and 232/377 female case/controls in cohort 1. In cohort 2, the numbers were 160/320 and 417/760, respectively. Among women in cohort 1, the odds ratio (OR) for MS by passive smoking at the age of 10-19 was 1.432 (p = 0.037) but in men it was 1.232 (p = 0.39). Among men in cohort 2, OR was 1.593 (p = 0.022) but among women it was only 1.102 (p = 0.44). CONCLUSION: Among never smokers, female MS cases were more often than female controls reported with passive smoking between the age of 10 and 19, and among smokers above the age of 19, male MS patients were more often than male controls reported with passive smoking.