Discussion
This scoping review sought to gain an understanding of the available literature on interventions for dysphagia rehabilitation among individuals with moderate to severe ABI. There has been a growth in the number of relevant studies within recent years, suggesting an increased focus on evidence-based dysphagia rehabilitation for this clinical population. However, among the included studies, there was significant variability with respect to study design, intervention type, and outcome measures. Furthermore, most of the studies reviewed included mixed etiological populations, wherein stroke subjects were included alongside, and frequently outnumbered, ABI subjects. Furthermore, apart from the two case reports identified, there were only two other studies which recruited an entirely ABI population (>1 participant). Taken together, the evidence base for dysphagia among those with ABI is weak.
Overall, ABI-specific literature related to dysphagia rehabilitation is limited, especially when compared to other neurological populations such as stroke (16). Often, rehabilitation approaches for dysphagia in stroke and ABI populations are similar (41). However, dysphagia interventions may not necessarily be generalizable to both populations due to the differing nature of the conditions themselves; ABI can be much more complex than stroke, particularly more diffuse brain injuries, and have different recovery rates for motor, sensory, and cognitive function long term (4, 16, 41). Continuing to mix these neurological populations in research studies may be inappropriate without first developing further knowledge in ABI alone and comparing it to existing stroke rehabilitation evidence. By doing so, the generalizability of interventions from the stroke literature to individuals with ABI can be determined. Thus, it is paramount that future studies should strive to recruit more homogeneous brain injury populations, or stratify results by etiology, to establish treatment effectiveness for each clinical population separately.
Currently, several interventions have been examined for dysphagia rehabilitation in the ABI population. However, many interventions were evaluated as a single modality, while only one study used an individualized, multimodal, interdisciplinary therapeutic approach (29). Dysphagia is a complex disorder that involves multiple components, including motor, cognitive, sensory, and coordination mechanisms (17, 42). Post ABI, dysphagia may be accompanied by comorbid deficits, which can vary across cognitive, communication, and behavioural domains (17, 42). Taken together, there is a lack of research examining the potential benefits of using multimodal interventions for dysphagia. It would be worthwhile to evaluate whether ABI populations benefit more from combined or multimodal interventions compared to singular treatments, as it has been suggested that the best way to optimize treatment is to use a multidisciplinary approach (2, 17).
The most examined interventions identified in this review (i.e., forms of electrical stimulation, individualized management programs, diet manipulations and oral care) were each supported by varying study designs, while the least common intervention types were each investigated by single studies. Overall, the included studies were evenly distributed in terms of the strength of evidence supporting a dysphagia intervention, with just over half (n=9) of the included studies being either level 1b or level 2 evidence, and the rest level 4 or lower. Although the body of literature for dysphagia rehabilitation in ABI includes five RCTs, the majority of these (31, 37, 40) investigated the same intervention (i.e., NMES). Thus, a large proportion of other interventions were supported by lower quality evidence. While some interventions lend themselves better to certain study designs, these results demonstrate the continued need for high quality studies with appropriate controls.
In addition to the variability in interventions and study designs, it is important to also note the significant heterogeneity of outcome measures used. This is not unusual in ABI research; a systematic review of assessment tools used in ABI research revealed a large degree of heterogeneity in measures used (43). A total of >700 instruments were identified, with the vast majority being used or mentioned in only a single study (43). Typically, outcome measures should reflect the type of intervention being studied. This scoping review found that even across similar interventions, outcome measures were still highly diverse. Future studies should aim for similar outcome assessment protocols, as well as those psychometrically validated for ABI, as this would aid in better comparing findings across studies and more accurately determining treatment effectiveness.