Outcome Reporting Bias in Clinical Trials Researching Disease-Modifying Therapy in Patients With Multiple Sclerosis

BACKGROUND AND OBJECTIVES: Outcome reporting bias occurs when publication of trial results is dependent on clinical significance, thereby threatening the validity of trial results. Research on immunomodulatory drugs in multiple sclerosis has thrived in recent years. We aim to comprehensively examine to what extent outcome reporting bias is present in these trials and the possible underlying factors.

METHODS: We identified clinical trials evaluating the efficacy and safety of immunomodulatory drugs in patients with multiple sclerosis (MS) registered in ClinicalTrials.gov after September 2007 and completed before the end of 2018. Information about study design, type of funding, and primary and secondary outcome measures was extracted from the registry. Timing of registration in relation to study initiation and subsequent amendments to the planned outcomes were reviewed. Publications related to these trials were identified in several bibliographic databases using the trial registration number. Registered primary and secondary outcomes were recorded for each trial and compared with outcomes in the publication describing the main outcomes of the trial.

RESULTS: A search of ClinicalTrials.gov identified 535 eligible registered clinical trials; of these, 101 had a matching publication. Discrepancies between registered and published primary and secondary outcomes were found in 95% of the trials, including discrepancies between the registered and published primary outcomes in 26 publications. Forty-four percent of the published secondary outcomes were not included in the registry. A similar proportion of registered and nonregistered reported primary efficacy outcomes were positive (favoring the intervention). Nonindustry-funded and open-label trials in MS were more prone to selective primary outcome reporting, although these findings did not reach statistical significance. Only two-thirds of the trials were registered in ClinicalTrials.gov before the trial start date, and 62% of trials made amendments in registered outcomes during or after the trial period.

DISCUSSION: Selective outcome reporting is prevalent in trials of disease-modifying drugs in people with MS. We propose methods to diminish the occurrence of this bias in future research.