Studies were eligible for inclusion where they reported on randomised controlled trials (RCTs), controlled trials (CCTs), and pre-post studies, provided they reported an objectively measured outcome.
The interventions of interest were specified as non-surgical devices (continuous positive airway pressure - CPAP; mandibular advancement splints; tongue retaining devices) or surgical procedures (surgery for coincident nasal obstruction; uvulopalatopharyngoplasty, with or without tonsillectomy; laser-assisted uvulopalatoplasty; uvulopalatal elevation palatoplasty, uvulectomy alone; radio frequency ablation of soft palate or tongue base; palatal stiffening techniques; tongue base suspension procedures).
Comparators could be another of the interventions, placebo, lifestyle modification techniques, or no intervention. Studies assessing adenoidectomy or tonsillectomy, either alone or in combination with each other, were not included.
Adults with non-apnoeic snoring (defined as an apnoea/hypopnoea index score of less than or equal to 5) who were eligible for any of the interventions, providing the diagnosis of obstructive sleep apnoea syndrome had been excluded by sleep study, were eligible for inclusion in the review. Snorers with specific related co-morbidities were also not included.
Studies were required to report one or more of the objective (snoring recording/acoustic analysis, polysomnography (PSG) or oximetry, cephalometric radiographs or MRI scans) or subjective (patient and partner questionnaires relating to symptoms, quality of life or quality of sleep, patient symptom scores) outcome measures of snoring, or on complications.
The majority of the included studies assessed surgical procedures (89%). These were broadly grouped as: uvulopalatopharyngoplasty versus laser-assisted uvulopalatoplasty; uvulopalatopharyngoplasty alone; laser-assisted uvulopalatoplasty alone; radio frequency ablation of the soft palate or tongue base; and palatial stiffening techniques. The included studies differed considerably in study design, sample size and duration of follow-up. Studies were pre-dominantly surgical case series that reported pre-post data. Overall 85% of studies only included patients with a diagnosis of non-apnoeic snoring. There was a trend for objective outcome measures to be reported for the shorter follow-up periods and subjective measures to be assessed at longer follow-up times.
Mean patient age in the included studies ranged from 40 to 50 years, although this ranged from 19 to 83 years across the papers. All studies included a higher percentage of males, ranging from 56 to 100%. Almost all recruited patients with a body mass index classified as 'overweight'. Studies usually took place in the otolaryngology department (or equivalent). Countries of origin included North America, Scandinavia, UK and Europe, with smaller numbers in Thailand, Turkey, Israel, Hong Kong and Australia. The reported outcome measures could be broadly categorised as polysomnography parameter results, subjectively assessed snoring, daytime sleepiness, and objectively assessed snoring measures.
Studies were selected by two independent reviewers; disagreements were resolved by discussion and a third reviewer where necessary.