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.