Protocol and registration
The study protocol was approved by the Ethics Committee of the Ahvaz Jundishapur University of Medical Sciences (IR.AJUMS.REC.1399.466), and it has been reported in the International Prospective Register of Systematic Reviews (PROSPERO) database (ID CRD42020199005).
Identification and selection of studies
The literature was searched for identifying the available research studies that assessed sexual dysfunction in men with multiple sclerosis. We used these criteria to select eligible studies: (1) prevalence of sexual dysfunction was reported and (2) sexual dysfunction was reported separately for men. Studies that reported the indicators without gender segregation and studies that have reported indicators only in women were excluded, because they were not applicable to the scope of the current study. The studies of adult men (over 18 years old) were included. Studies with any form of sexual dysfunction were included (e.g., ED, impotence, retrograde ejaculation, delayed ejaculation). The cross-sectional studies were included. Moreover, original researches in the form of community-based studies, cross-sectional studies, observational cohorts, and case-control studies considering the prevalence of sexual dysfunction in MS patients were considered acceptable for inclusion.
A systematic search of international literature databases and the Iranian literature databases was performed in December 2019 without time limitation with a research librarian. The international databases searched were Web of Science, PubMed, Scopus, and Embase, and the Iranian literature databases searched were Magiran, SID, and Iran Medical Papers Database. The relevant Medical Subject Heading (MeSH) terms and keywords “multiple sclerosis”, “Sexual dysfunctions”, “Men”, “Prevalence”, and their synonyms were used in various combinations using Boolean operators like “OR” or “AND”. The search was limited to papers published in English and Persian and humanities’ subjects because of time and resource limitation. To access more relevant papers, the researchers searched the reference lists of relevant literature manually. References were managed using EndNote X8.1.
All titles, abstracts, and full-text articles were screened by two reviewers independently, MZ and RM. In case of disagreement, it was resolved by discussion, and in case of disagreement, a third independent party (MD) decided as an arbiter.
The items extracted by one reviewer were also checked for accuracy by another reviewer. The items extracted from each article included year of publication, country/city, sample size, response rate, age range and mean age, duration of MS, design of the study, the outcome of study, scale/index, the method of outcome assessment, and prevalence (N of event).
Measure of research quality
The quality assessment was screened by two reviewers independently. In case of disagreement, it was resolved by discussion, and in case of further disagreement, a third independent party decided as an arbiter. We assessed the quality of studies through the “Quality Assessment Checklist for Prevalence Studies.” The total score of 0–3, 4–6, and 7–9 indicate the low, moderate, and high risk of bias, respectively. Based on the checklist, the studies with a high risk of bias were excluded .
Meta-analysis was performed using the random effects model with the inverse variance-weighted method to estimate the overall prevalence of sexual dysfunction in men with MS. I2 was used to assess the studies’ heterogeneity. Therefore, meta-regression was used to determine potential sources of heterogeneity, and items used in the meta-regression included mean age, sample size, mean duration of MS, and the Expanded Disability Status Scale (EDSS) score. Egger’s test was used to evaluate the publication bias. Stata software 12 was used for data analysis.