Relationship between early clinical characteristics and long term disability outcomes: 16 year cohort study (follow-up) of the pivotal interferon ß-1b trial in multiple sclerosis.

BACKGROUND: Evaluating the long term benefit of therapy in multiple sclerosis (MS) is challenging. Although randomised controlled trials (RCTs) demonstrate therapeutic benefits on short term outcomes, the relationship between these outcomes and late disability is not established. METHODS: In a patient cohort from the pivotal interferon ß-1b trial, the value of clinical and MRI measures were analysed, both at baseline and during the RCT, for predicting long term physical and cognitive outcome. RESULTS: Baseline disability correlated with both physical (R(2)=0.22; p<0.0001) and cognitive (R(2)=0.12; p<0.0001) outcome after 16 years. Accrual of disability during the RCT (R(2)=0.12; p<0.0001) and annualised relapse rates during the trial correlated with physical outcome (R(2)=0.12; p<0.0001) but not with cognition. In contrast, baseline MRI measures of atrophy and lesion burden correlated with cognitive (R(2)=0.21; p<0.0001), but not with physical, outcome. Accumulation of plaque burden measured by MRI did not correlate with late physical disability or with cognitive outcome. Multivariate regression analysis using stepwise elimination demonstrated that baseline variables contributed independently to predicting long term outcomes while trial outcome variables contributed little. Overall, and considerably dependent on baseline measures, the models developed by this method accounted for approximately half of the variance in long term cognitive and disability outcome. CONCLUSIONS: Although on-trial change in some short term clinical measures correlated with long term physical and disability outcomes, the proportion of the variance explained by single commonly employed on-study variables was often small or undetectable. Better correlations were observed for several baseline measures, suggesting that long term outcome in MS may be largely determined early in the disease course. Trial registration number http://Clinical Trials.gov, study registration NCT00206635.

Establishing long-term efficacy in chronic disease: use of recursive partitioning and propensity score adjustment to estimate outcome in MS.

CONTEXT: Establishing the long-term benefit of therapy in chronic diseases has been challenging. Long-term studies require non-randomized designs and, thus, are often confounded by biases. For example, although disease-modifying therapy in MS has a convincing benefit on several short-term outcome-measures in randomized trials, its impact on long-term function remains uncertain. OBJECTIVE: Data from the 16-year Long-Term Follow-up study of interferon-beta-1b is used to assess the relationship between drug-exposure and long-term disability in MS patients. DESIGN/SETTING: To mitigate the bias of outcome-dependent exposure variation in non-randomized long-term studies, drug-exposure was measured as the medication-possession-ratio, adjusted up or down according to multiple different weighting-schemes based on MS severity and MS duration at treatment initiation. A recursive-partitioning algorithm assessed whether exposure (using any weighing scheme) affected long-term outcome. The optimal cut-point that was used to define "high" or "low" exposure-groups was chosen by the algorithm. Subsequent to verification of an exposure-impact that included all predictor variables, the two groups were compared using a weighted propensity-stratified analysis in order to mitigate any treatment-selection bias that may have been present. Finally, multiple sensitivity-analyses were undertaken using different definitions of long-term outcome and different assumptions about the data. MAIN OUTCOME MEASURE: Long-Term Disability. RESULTS: In these analyses, the same weighting-scheme was consistently selected by the recursive-partitioning algorithm. This scheme reduced (down-weighted) the effectiveness of drug exposure as either disease duration or disability at treatment-onset increased. Applying this scheme and using propensity-stratification to further mitigate bias, high-exposure had a consistently better clinical outcome compared to low-exposure (Cox proportional hazard ratio = 0.30-0.42; p<0.0001). CONCLUSIONS: Early initiation and sustained use of interferon-beta-1b has a beneficial impact on long-term outcome in MS. Our analysis strategy provides a methodological framework for bias-mitigation in the analysis of non-randomized clinical data. TRIAL REGISTRATION: Clinicaltrials.govNCT00206635.

Long-term follow-up of the original interferon-beta1b trial in multiple sclerosis: design and lessons from a 16-year observational study.

OBJECTIVE: This article describes the design of and difficulties inherent in the execution of a long-term, observational trial that sought to assess the validity of short-term measures of multiple sclerosis (MS) (eg, relapse rate, inflammatory lesions) for long-term disease outcomes. METHODS: In the original double-blind, placebo-controlled interferon (IFN)-p1b study, 372 patients with relapsing-remitting MS (Expanded Disability Status Scale score 0.0-5.5) were randomly assigned to IFN-beta1b 50 ug (n = 125), IFN-beta1b 250 microg (n = 124), or placebo (n = 123) for 2 years. These patients were recruited 16 years later for participation in this long-term follow-up (LTF) study, which had no exclusion criteria or drug interventions. RESULTS: The 11 centers identified 88.2% (328/372) of the original study patients at LTF; however, 10.8% (n = 40) refused to participate and 9.4% (n = 35) were deceased. Detailed evaluations were available for 260 patients, which included 7 deceased patients. No differences in demographic or baseline disease characteristics were found between individuals who did and did not participate in the LTF. More patients randomly assigned to placebo in the original trial were deceased (20/123 [16.3%]) than those assigned to IFN-beta1b 50 microg (9/125 [7.2%]; uncorrected P = 0.044) or IFN-beta1b 250 microg (6/124 [4.8%]; uncorrected P = 0.003). CONCLUSIONS: Although most patients (88.2%) were identified at LTF, ascertainment was incomplete. This was attributable to patients' refusal to participate, loss to follow-up, or death. Delays in the registration of death data and recent privacy legislation provided further barriers. Mortality was lower for patients originally randomized to receive IFN-beta1b rather than placebo. We recommend that all short-term trials on chronic diseases include provisions for LTF.