Impact of methodological choices in comparative effectiveness studies: application in natalizumab versus fingolimod comparison among patients with multiple sclerosis

Background

Natalizumab and fingolimod are used as high-efficacy treatments in relapsing–remitting multiple sclerosis. Several observational studies comparing these two drugs have shown variable results, using different methods to control treatment indication bias and manage censoring. The objective of this empirical study was to elucidate the impact of methods of causal inference on the results of comparative effectiveness studies.

Methods

Data from three observational multiple sclerosis registries (MSBase, the Danish MS Registry and French OFSEP registry) were combined. Four clinical outcomes were studied. Propensity scores were used to match or weigh the compared groups, allowing for estimating average treatment effect for treated or average treatment effect for the entire population. Analyses were conducted both in intention-to-treat and per-protocol frameworks. The impact of the positivity assumption was also assessed.

Results

Overall, 5,148 relapsing–remitting multiple sclerosis patients were included. In this well-powered sample, the 95% confidence intervals of the estimates overlapped widely. Propensity scores weighting and propensity scores matching procedures led to consistent results. Some differences were observed between average treatment effect for the entire population and average treatment effect for treated estimates. Intention-to-treat analyses were more conservative than per-protocol analyses. The most pronounced irregularities in outcomes and propensity scores were introduced by violation of the positivity assumption.

Conclusions

This applied study elucidates the influence of methodological decisions on the results of comparative effectiveness studies of treatments for multiple sclerosis. According to our results, there are no material differences between conclusions obtained with propensity scores matching or propensity scores weighting given that a study is sufficiently powered, models are correctly specified and positivity assumption is fulfilled.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12874-022-01623-8.

Natalizumab Versus Fingolimod in Patients with Relapsing-Remitting Multiple Sclerosis: A Subgroup Analysis From Three International Cohorts

INTRODUCTION

Natalizumab has proved to be more effective than fingolimod in reducing disease activity in relapsing-remitting multiple sclerosis (RRMS). Whether this association is universal for all patient groups remains to be determined.

OBJECTIVE

The aim of this study was to compare the relative effectiveness of natalizumab and fingolimod in RRMS subgroups defined by the baseline demographic and clinical characteristics of interest.

METHODS

Patients with RRMS who were given natalizumab or fingolimod were identified in a merged cohort from three international registries. Efficacy outcomes were compared across subgroups based on patients' sex, age, disease duration, Expanded Disability Status Scale (EDSS) score, and disease and magnetic resonance imaging (MRI) activity 12 months prior to treatment initiation. Study endpoints were number of relapses (analyzed with weighted negative binomial generalized linear model) and 6-month confirmed disability worsening and improvement events (weighted Cox proportional hazards model), recorded during study therapy. Each patient was weighted using inverse probability of treatment weighting based on propensity score.

RESULTS

A total of 5148 patients (natalizumab 1989; fingolimod 3159) were included, with a mean ± standard deviation age at baseline of 38 ± 10 years, and the majority (72%) were women. The median on-treatment follow-up was 25 (quartiles 15-41) months. Natalizumab was associated with fewer relapses than fingolimod (incidence rate ratio [IRR]; 95% confidence interval [CI]) in women (0.76; 0.65-0.88); in those aged ≤ 38 years (0.64; 0.54-0.76); in those with disease duration ≤ 7 years (0.63; 0.53-0.76); in those with EDSS score < 4 (0.75; 0.64-0.88), < 6 (0.80; 0.70-0.91), and ≥ 6 (0.52; 0.31-0.86); and in patients with pre-baseline relapses (0.74; 0.64-0.86). A higher probability of confirmed disability improvement on natalizumab versus fingolimod (hazard ratio [HR]; 95% CI) was observed among women (1.36; 1.10-1.66); those aged > 38 years (1.34; 1.04-1.73); those with disease duration > 7 years (1.33; 1.01-1.74); those with EDSS score < 6 (1.21; 1.01-1.46) and ≥ 6 (1.93; 1.11-3.34); and patients with no new MRI lesion (1.73; 1.19-2.51).

CONCLUSIONS

Overall, in women, younger patients, those with shorter disease durations, and patients with pre-treatment relapses, natalizumab was associated with a lower frequency of multiple sclerosis relapses than fingolimod. It was also associated with an increased chance of recovery from disability among most patients, particularly women and those with no recent MRI activity.

[Fampridine and multiple sclerosis]

The background for the use of fampridine, the indications, contraindications, side effects, and recommendations for Danish patients with multiple sclerosis are reviewed.

[Diagnosis of multiple sclerosis--the 2010 revision of the McDonald criteria]

The 2010 revision of the McDonald diagnostic criteria for multiple sclerosis is reviewed. The diagnostic criteria have been simplified, which allows earlier diagnosis and treatment of multiple sclerosis.

[Magnetic resonance imaging in the diagnosis and follow-up of multiple sclerosis]

The use of MRI in MS diagnosis and follow-up is reviewed. The acquirements to the MRI protocol given by the revised McDonald diagnostic criteria are discussed.

[Diagnosis of multiple sclerosis: revision of the McDonald criteria]

The 2005 revision of the McDonald diagnostic criteria for multiple sclerosis is reviewed. A standard clinical approach to the diagnosis of multiple sclerosis, including the use of a standard MRI protocol, VEP, CSF evaluation and other paraclinical tests is suggested.

[Functional magnetic resonance imaging in multiple sclerosis]

The use of functional magnetic resonance imaging (fMRI) in multiple sclerosis (MS) is reviewed. fMRI is an efficient method to map brain activity non-invasively and has shown that adaptive cortical changes take place as a consequence of demyelination and tissue loss in MS. These changes may help to maintain normal function in the course of MS, and to some extent they might explain the moderate correlation between conventional MRI findings and disability. fMRI can provide information about brain plasticity and thus improve our understanding of the disease.

Neutralizing antibodies hamper IFN bioactivity and treatment effect on MRI in patients with MS

We measured neutralizing antibodies (NABs) and the in vivo biologic response to interferon-beta on neopterin and beta(2)-microglobulin blood levels. All NAB-negative patients had an in vivo biologic response (full or partial), whereas all high-level positive patients had no response. High-level NAB patients had more MRI activity than NAB-negative patients (p = 0.031). Patients with a full response had less MRI activity than patients without biologic response (p = 0.032).

The relationship between MRI and PET changes and cognitive disturbances in MS

Cognitive dysfunction in multiple sclerosis (MS) is present in approximately 50% of the patients. Only moderate correlations have been found between cognitive dysfunction and T(2) lesion load, black holes or atrophy. Cognitive dysfunction in MS is probably related to the overall disease burden of the brain including abnormalities in normal appearing white matter (NAWM) and cortical grey matter, which is undetected with conventional magnetic resonance imaging (MRI). Hence, imaging techniques that embrace such abnormalities are needed to achieve better correlation with cognitive dysfunction. MR spectroscopy (MRS) performed with multi-slice echo planar spectroscopic imaging (EPSI) and PET measurements of brain metabolism as the cortical cerebral metabolic rate of glucose are imaging methods that are able to provide information on axonal loss or dysfunction in both MS lesions and in NAWM and cortical grey matter. Measurements of global NAA using multi-slice EPSI is a new promising method for measurement of the global neuron capacity and can be repeated with only little discomfort and without any risk for the patient.

Correlation of Global N-Acetyl Aspartate With Cognitive Impairment in Multiple Sclerosis

BACKGROUND

Whole-brain N-acetyl aspartate (NAA), a measure of neuronal function, can be assessed by multislice echo-planar spectroscopic imaging.

OBJECTIVE

To test the hypothesis that the global brain NAA/creatine (Cr) ratio is a better predictor of cognitive dysfunction in multiple sclerosis than conventional magnetic resonance imaging measures.

DESIGN

Survey.

SETTING

Research-oriented hospitals.

PATIENTS

Twenty patients, 16 women and 4 men (mean age, 36 years), with early relapsing-remitting multiple sclerosis (mean Expanded Disability Status Scale score, 2.5).

MAIN OUTCOME MEASURES

Correlation between the global NAA/Cr ratio and a cognitive dysfunction factor comprising 16 measures from an extensive neuropsychological test battery that best distinguished patients with multiple sclerosis from healthy control subjects.

RESULTS

A significant partial correlation between the global NAA/Cr ratio and the cognitive dysfunction factor was found (partial r = 0.62, P = .01), and 9 cognitively impaired patients had significantly lower global NAA/Cr ratios than 11 unimpaired patients (P = .04). No significant correlations were found between the cognitive dysfunction factor and conventional magnetic resonance imaging measures (ie, brain parenchymal fraction and lesion volume).

CONCLUSIONS

Multislice echo-planar spectroscopic imaging provides global metabolic measures that distinguish between cognitively impaired and unimpaired patients with multiple sclerosis and correlate with a global cognitive measure. Standardization of the technique is needed, and larger-scale studies that include healthy controls are suggested.

[Proton magnetic resonance spectroscopy in the evaluation of cognitive disturbances]

Magnetic resonance spectroscopy can detect metabolic changes in the brain, including changes in N-acetyl aspartate, a metabolite generally believed to be a marker of neuronal integrity. The correlations between metabolic changes and cognitive status in normal subjects and in a range of neurological and psychiatric disorders are reviewed. Magnetic resonance spectroscopy seems to be a way to monitor the efficacy of existing and new treatments to prevent the development of cognitive deficits in a number of diseases.

Multi-slice echo-planar spectroscopic MR imaging provides both global and local metabolite measures in multiple sclerosis

MR spectroscopy (MRS) provides information about neuronal loss or dysfunction by measuring decreases in N-acetyl aspartate (NAA), a metabolite widely believed to be a marker of neuronal viability. In multiple sclerosis (MS), whole-brain NAA (WBNAA) has been suggested as a marker of disease progression and treatment efficacy in treatment trials, and the ability to measure NAA loss in specific brain regions early in the evolution of this disease may have prognostic value. Most spectroscopic studies to date have been limited to single voxels or nonlocalized measurements of WBNAA only, and longitudinal studies have often been hampered by standardization and reproducibility problems. Multi-slice echo-planar spectroscopic imaging (EPSI) is presented as a promising alternative to single-voxel or nonlocalized spectroscopy for obtaining global metabolite estimates in MS. In the same session, measurements of metabolites in specific brain areas chosen after image acquisition (e.g., normal-appearing white matter (NAWM), gray matter (GM), and lesions) can be obtained. The identification and exclusion of regions that are inadequate for spectroscopic evaluation in global assessments can significantly improve quality and reproducibility, as demonstrated by a low within-subject variance in healthy controls. The reproducibility of the technique makes it a promising tool for future longitudinal spectroscopic studies of MS.

[Magnetic resonance and multiple sclerosis I. Conventional diagnostic techniques]

Conventional magnetic resonance imaging (MRI) is still the standard technique in the diagnosis and follow-up of patients with multiple sclerosis (MS), despite low pathological specificity and poor correlation to the disability. The results of T2- and T1-weighted imaging with and without contrast and the lesion characteristics are presented in this review. The numerous differential diagnoses and the diagnostic MRI criteria are also reviewed.

[Magnetic resonance and multiple sclerosis II. New diagnostic techniques]

Conventional magnetic resonance imaging (MRI) techniques have proved important in the diagnosis and in the follow-up in clinical trials of patients with multiple sclerosis (MS). However, these techniques have low specificity for the pathological changes in the MS lesions, and the correlation between conventional MRI and the disability is poor. The last ten years have seen the development of new techniques with improved sensitivity and increased pathological specificity, such as magnetisation transfer imaging (MTI), magnetic resonance spectroscopy (MRS), diffusion-weighted imaging, and functional magnetic resonance imaging (fMRI). These techniques and their contribution to the knowledge about the pathophysiology of MS are described in this review.