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As discussed inChapter 3(seeStudy selection), the review included 19 studies assessing a range of interventions, including pharmacological treatments, mechanical devices for pressure equalisation and several types of surgery. All studies reported relevant outcomes relating to effectiveness and some reported safety data. However, there was a paucity of high-quality research and the informativeness of the evidence base was limited by numerous factors.

Differences in patient characteristics

There is a lack of consensus on how ETD should be defined, as well as on the aetiology of the condition. This lack of consensus was reflected in the considerable variation in inclusion criteria employed in the included studies, and, consequently, in the characteristics of the patients treated in these studies.

The included studies, which required patients to have a clinical diagnosis of ETD, exhibited substantial variation in whether or how ETD was defined. Some studies simply reported that patients were required to have ETD, without further details. Even when precise symptoms that were considered necessary for a diagnosis of ETD were reported, the baseline severity and/or frequency of the symptoms were rarely quantified. It was, therefore, often unclear what the precise characteristics of the patient population were in relation to some or all of the criteria which may be considered to form part of the characterisation of ETD.

Studies also varied whether they required patients to have failed previous treatments or to have

experienced symptoms for a particular duration. Studies of pharmacological interventions and mechanical devices did not specify duration of symptoms or that patients should have failed previous medical

interventions, while several studies of surgical interventions required that patients should have failed multiple attempts at medical management and, in some cases, prior surgical intervention.

Another key difference between the non-surgical and surgical studies was that all except one of the non-surgical studies were conducted in mixed populations of adults and adolescents or children. In the fifth study, it was unclear whether or not this was also the case.40_{Unlike non-surgical interventions, studies}

of surgical interventions were available in exclusively adult populations.

Despite poor reporting of ETD history, it also appeared that, as might be anticipated, patients in the non-surgical studies might have had less serious or long-lasting ETD than those in the surgical studies. Within-study variation in these characteristics was also seen in several studies assessing surgical interventions. A minority of studies excluded patients with specified comorbidities, while other studies reported that some or all of the patients had these conditions (e.g. rhinosinusitis, allergies or reflux). In three of the surgical studies, it was clear that all patients had chronic otitis media with effusion related to ETD, and that their prognosis was consequently poorer than that of patients in other studies. Finally, there was variance in studies of all types of intervention with regard to whether or not an intact tympanic membrane was required, whether or not patients were required to have an abnormal otological

examination, and whether or not an abnormal tympanogram was required. In several studies, poor reporting meant that it was unclear which baseline tests were employed and whether or not test results formed part of the inclusion criteria for the study.

Outcome assessment

Assessment methods were not well defined in most studies. This was a particular issue for the primary review outcome of patient reported symptoms. While a majority of the studies reported some information on this outcome, most of the studies, as with baseline assessment, reported only presence, remission or improvement of symptoms, rather than quantifying them using a validated scale. As with baseline assessment and/or inclusion criteria, some studies reported assessment of specific ETD symptoms, while others reported global improvement or improvement in unspecified symptoms. Owing to the level of symptoms experienced at baseline and follow-up being unclear, it was, therefore, also difficult to ascertain whether or not different studies were assessing comparable symptomatology. Exceptions to this were four studies, which all reported that they measured symptom severity before and after treatment using VASs or a form of the ETDQ-7.20,40,52,55

Variability in the measure used was an issue for other outcomes, although to a lesser degree. Although data on middle ear function were reported by a majority of studies, a number of different tests were used to assess this, including tympanometry, ability to perform the Valsalva manoeuvre, and appearance on otological examination. Most studies which assessed hearing used a recognised measure such as pure-tone audiometry or air–bone gap.

Follow-up

Even where outcomes were consistently reported, a key issue was the variation between studies in duration of follow-up, which made the meaningful synthesis of data between the studies impossible.

An extremely wide range in its duration was found. Two of the three studies of pharmacological agents had extremely short follow-up periods of 30 minutes and 1 to 4 hours.24,25_{These were too short for the}

data obtained to have any clinical relevance. Therefore, further work with appropriate longer-term

assessment of efficacy and safety would be required to adequately assess these interventions. Follow-up in the third pharmacological study was reasonable, although relatively short term (6 weeks).52_Follow-up

in the two studies of mechanical devices was short (1 week)40_{or unclear.}41

Follow-up in the studies of surgical interventions also varied considerably, from a few weeks to 2 years or longer. In some cases, mean duration of follow-up was reported, with or without an indication of the range of follow-up time, and data appeared to have been aggregated from patients assessed at different time points.

Conversely, some studies reported follow-up data for all or a majority of patients at multiple time points; in some cases, this appeared to demonstrate continuing improvement over time. This may represent a true accrual of higher levels of benefit from surgery over time, or it may be reflective of remission of symptoms due to the natural course of the condition. As all except one of the studies of surgery were uncontrolled studies, and the single controlled study reported very limited data on outcomes for the control group, it is not possible to determine the cause of the apparent improvement over time. Lack of adequate long-term follow-up is a serious concern in relation to surgical interventions such as tuboplasty, where the procedure may have ongoing implications for middle ear function. For some studies, this uncertainty is additional to the difficulty in determining the effect of the assessed intervention when cointerventions have also been administered.

Interventions and cointerventions

For the small number of interventions where there was more than one study, the details of the interventions varied; there were differences in the surgical technique or pressure applied in studies of tuboplasty and balloon dilatation, respectively. In addition to differences in the primary intervention, many of the studies of surgical interventions reported cointerventions administered concurrently with or subsequent to the intervention being assessed.18,20–23,55,56,61_{As many of these cointerventions were}

additional sinonasal or otological surgical procedures, it is not possible to determine whether the observed treatment benefits are attributable to the primary intervention or to one or more of the additional

treatments. The majority of the surgical evidence base was impacted by the use of cointerventions. In studies of pharmacological agents and devices, cointervention appeared to be less of an issue, with only the RCT of nasal steroids documenting use of additional pharmacological agents.52_{In this instance, the use}

of cointerventions was recorded and used to inform a secondary analysis of overall efficacy. The extremely short follow-up and laboratory-based design of the other two pharmacological studies means that use of cointerventions appears unlikely. However, because reporting of the other non-surgical studies was, in some cases, limited, it is difficult to be certain that participants did not use cointerventions in the studies of mechanical devices.