Types of studies

We assessed RCTs and quasi‐RCTs. Quasi‐RCTs are trials in which allocation of participants is partly systematic (e.g. by medical record number or by alternation). We included quasi‐RCTs because of the paucity of studies in this area. We reported other studies, including observational studies, in the Discussion. We have considered adverse events taking observational studies into account in the Discussion. We also planned to discuss economic issues in the 'Discussion', but there was insufficient information in the included studies.

We considered published or unpublished studies in any language.

Types of participants

We included adults or children who presented with an idiopathic facial palsy which was diagnosed as Bell's palsy. We excluded those who were diagnosed as having herpes zoster, those who had a traumatic aetiology, or other identified aetiology from the review. This included any cases of recurrent and familial Bell's palsy or Melkersson‐Rosenthal syndrome.

Types of interventions

We included any surgical intervention carried out for Bell's palsy. We compared these interventions to no treatment, later treatment (beyond three months), sham treatment, other surgical treatments or medical treatment. Where concomitant treatment was given, this was the same in both treatment and comparator groups. For this review, 'early' surgical intervention was defined as operations occurring within three months of facial paralysis onset, and 'late' surgical intervention was defined as operations occurring later than three months after facial paralysis onset. A time frame of three months or less was decided upon as throughout literature, there has been inconsistent reporting of the effects of decompression surgery in relation to specific time points, as explored in How the intervention might work. Given the fact that studies have reported cases with facial nerve inflammation as late as three to four months post onset (via gadolinium enhancement on MRI and intraoperative oedematous swelling) and that no high‐quality evidence currently exists to discredit operating within a shorter timeframe, we decided studies investigating facial nerve decompression within three months should not be excluded from our analysis. Furthermore, the variability in facial nerve segments decompressed and surgical approaches used makes it more difficult to evaluate the efficacy of certain time points for establishing inclusion criteria. Therefore, we excluded studies where participants were operated on during the later stages of their recovery (after more than three months). In cases where studies reported outcomes from both early and late operations, we included the early treatment arm as the intervention group and the late treatment arm as a comparator.

Should future studies report on surgery within earlier time frames (immediately after onset, within two weeks of onset, etc.), these studies will be considered for inclusion of subsequent review updates.

Types of outcome measures

We did not use measurement of the review outcomes to determine study eligibility.

Electronic searches

The Cochrane Neuromuscular Information Specialist searched the following databases for this update:

• the Cochrane Neuromuscular Specialised Register via the Cochrane Register of Studies (CRS‐Web; 20 March 2020; Appendix 1);

• the Cochrane Central Register of Controlled Trials (CENTRAL) via the Cochrane Register of Studies (CRS‐Web; 20 March 2020; Appendix 2);

• MEDLINE OvidSP (1946 to 19 March 2020; Appendix 3);

• Embase OvidSP (1974 to 2020 week 11; Appendix 4);

• US National Institutes of Health Ongoing Trials Register ClinicalTrials.gov (20 March 2020; www.clinicaltrials.gov; Appendix 1); and

• the World Health Organization International Clinical Trials Registry Platform (20 March 2020; www.who.int/ictrp/en/; Appendix 2).

Searching other resources

We reviewed the bibliographies of all trials identified.

We performed a handsearch of the following conference abstracts:

• American Academy of Otolaryngology – Head and Neck Surgery Annual Meeting 2006 and 2007; and

• British Academic Conference in Otolaryngology and ENT Expo Birmingham, UK, both 2006.

Selection of studies

Two review authors (DW and KA) independently reviewed titles and abstracts identified by the search strategy. For a 2020 top‐up search, an Information Specialist performed an initial screen of titles and abstracts for RCTs. The review authors obtained the full text of all relevant studies and assessed them independently. Three review authors (DW, KA and IM) assessed whether each trial met the inclusion criteria. They resolved any disagreements by discussion with the lead author (IM) where required. We included a PRISMA flow chart to illustrate the study selection process (Figure 1; Moher 2015).

Figure 1

---

---

Study flow diagram.

Data extraction and management

For the previous version of the review, two review authors (DW and KA) independently extracted the data and entered them onto a specifically designed form. The extracted data included characteristics of study participants, methods, interventions used, outcomes and results. Two review authors (DW and KA) entered the data for Mechelse 1971 into Review Manager 5. For the update, IM and an independent systematic reviewer independently extracted data from the newly included study and documented differences between the extractions. IM entered data into Review Manager 5, checked outcome data entry and spot‐checked characteristics of studies data. Differences were resolved via discussion between IM and a third review author (KM) who had not extracted data. For the update, we extracted additional characteristics of studies data (e.g. funding sources and conflicts of interest). For studies written in languages other than English, translators provided us with a translation for us to perform a data extraction. The lead author (IM) checked extracted numerical data against the trial report, as far as possible. For future updates, we will adapt the data extraction form as necessary and pilot it among review authors before use.

Assessment of risk of bias in included studies

Three review authors (IM, DW and KM) independently assessed the risk of bias across seven 'Risk of bias' domains: sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective outcome reporting and 'other sources of bias'. We judged each study in relation to each domain, as at a high, low or unclear risk of bias. We resolved any disagreement by discussion with the lead author (IM). When considering treatment effects, three review authors (IM, DW and KM) considered the risk of bias for the studies that contributed to that outcome. The review authors made summary assessments for the 'Risk of bias' for each important outcome (across domains), according to the criteria outlined in Table 1 (Higgins 2011).

Measures of treatment effect

There were insufficient studies to enable any statistical analysis. If in future updates statistical analysis is possible, we will enter data into the Review Manager 5 when available and analyse the data using the standard statistical methods (Review Manager 2014). For continuously measured outcomes, we will use means to obtain mean differences (MDs) with 95% confidence intervals (CIs), or standardised mean differences for results across studies with outcomes that are conceptually the same but measured in different ways. For dichotomous outcome data, we will estimate the pooled risk ratio (RR) with 95% CI within Review Manager 5. We will calculate the number needed to treat for an additional beneficial effect (NNTB) or for an additional harmful effect (NNTH) if possible.

Unit of analysis issues

Where multiple trial arms are reported in a single trial, we included only the treatment arms relevant to the review topic, but list them all in the Characteristics of included studies table. The Li 2016a study had multiple eligible arms.

We describe the approach to unit‐of‐analysis issues in meta‐analysis in Appendix 3.

Dealing with missing data

The review authors did not contact trial authors for additional data or to verify study characteristics.

Assessment of heterogeneity

We did not assess heterogeneity due to lack of data. See Appendix 3 for planned methods.

Assessment of reporting biases

There were insufficient studies to enable any statistical analyses or to allow use of funnel plots.

If searches had identified trial protocols, clinical trial registrations or abstracts indicating the existence of unpublished studies, we would have attempted to determine their status by contacting the investigators and would have reported on potential unpublished studies in the review.

We would also have considered the effects of reporting biases – whether of studies or selective outcome reporting – on our findings, during the GRADE assessment.

Data synthesis

We would have considered different types of surgery separately, other than minor variations in technique, such as within the retro‐auricular/transmastoid. We considered different comparators separately, assessing the components of any comparator interventions (e.g. 'usual care' or 'standard care') to determine whether they were sufficiently similar for pooling to be feasible.

There were insufficient studies to enable any statistical analyses. We reported methods to be used if meta‐analysis is possible in future in Appendix 3.

This review has a published protocol (Swan 2008). We have documented changes from the protocol in Differences between protocol and review.

Subgroup analysis and investigation of heterogeneity

We did not perform subgroup analyses or investigate heterogeneity for lack of data. See Appendix 3 for planned methods.

Sensitivity analysis

We did not perform sensitivity analyses for lack of data. See Appendix 3 for planned methods.

Summary of findings and assessment of the certainty of the evidence

We selected the following outcomes for presentation in 'Summary of findings' tables.

• Recovery of facial nerve function at 12 months.

• Side effects and complications of treatment.

We used Review Manager 5 to create a 'Summary of findings' table (Review Manager 2014).

We used the five GRADE considerations (study limitations, consistency of effect, imprecision, indirectness and publication bias) to assess the certainty of a body of evidence (studies that contributed data for the prespecified outcomes). We used methods and recommendations described in Chapters 11 and 12 of the Cochrane Handbook for Systematic Reviews of Interventions (Schünemann 2020a; Schünemann 2020b). We considered RCTs as high‐certainty evidence if the five factors above were not present to any serious degree. We downgraded the certainty of evidence once if there were any individual GRADE considerations present to a serious degree and twice if very serious, to produce judgements of moderate, low or very low certainty. We justified all decisions to downgrade or upgrade the certainty of evidence using footnotes. Table 1 outlines our approach for summary assessments of the risk of bias for each important outcome (across domains) within and across studies (Higgins 2011).