Title: Mapping acute lesion locations to physiological swallow impairments after stroke
Authors: Wilmskoetter, Bonilha, Martin-Harris, Elm, Horn, & Bonilha
Journal: NeuroImage: Clinical
Year of Publication: 2019
Design Type: Retrospective observational cross-sectional
Purpose: “The goal of this study was to assess the critical location of supra-tentorial stroke lesions associated with fine-grained disruptions in swallow physiology defined as the movement of swallow relevant structures in relation to bolus flow patterns.”
Population: 68 acute first-ever ischemic stroke patients admitted to Medical University of South Carolina between 2008-2017 (on stroke service)
Inclusion criteria: diagnostic MRI including diffusion-weighted sequences (DW-MRI) and MBSS during hospital stay
Exclusion criteria: history of and/or neuroimaging evidence of previous stroke; history of diseases related to dysphagia (e.g. head neck cancer, Parkinson, dementia); neurological worsening between MRI and MBSS; < 21 years old
- Only got a sec?
- Specific lesions showed a relationship for specific swallowing physiological impairments in laryngeal elevation, anterior hyoid excursion, laryngeal vestibular closure, and pharyngeal residue (see image at end of article)
- Only got a minute?
- “our study implicates that bilateral brain networks are crucial for swallow physiology, but that the right hemisphere, especially sensorimotor integration networks, contributes more than the left hemisphere”
- “We found significant lesion-impairment relationships for only three out of 85 timing measures, two out of 50 distances and areas measures, and none of the hyoid speed measures”
- “In contrast to significant lesion-impairment relationships for separate swallow components, we did not find any relationships between global swallow impairment scores–MBSImP oral total and pharyngeal total sum scores, PCA factor scores–and lesion locations”
- Got more time? Keep reading!!
Remember your undergraduate and/or graduate neuroanatomy course? I know some loathed it and some loved it. For me, I was in my element, so much so that I was sure my initial passion was going to be everything-neuro-TBI-related. While I still LOVE neuro and have had my share of experience within this realm for sure, reading this article brought me back to my first love, while also mixing in my more recent and exciting infatuation for dysphagia.
I’m sure we’ve all known for many years that swallowing is related to the brain, more than that, the brain controls how the swallowing muscles work, when they work, and to what degree. Going even deeper, these muscles are also controlled by parts of the brain that not only control the motor movements of the muscles, but also the sensations the nerves experience during swallowing. Obviously, we’re talking about something incredibly intricate, detailed, and specific, but still manages to make up this huge amazing network when it’s all put together. Trying to conceptualize this, my brain automatically went to the famously layered pointillism painting “A Sunday Afternoon on the Island of La Grande Jatte” (from my #1 fave movie Ferris Bueller’s Day Off at the musuem):
We’re still working as a field to try to begin to understand how all these parts work together to form an effortless, beautiful, safe swallow and also how their functions can cause separate impairments related to swallowing function. But you have to admit just how COOL it could be for us to know, based on specific sites of lesion, what specific swallow impairments we could expect to see before/after our clinical bedside swallow exams (and instrumentals), and then be able to determine more quickly and accurately the specific, individualized treatment programs for each patient?!?!
Sorry, the SLP nerding out got a bit over-excited there🤓. And I know I’m a long way off (maybe in the next decade??), but like I said, neuro in general excites me, and knowing the future possibilities gets my blood pumping all over again.😍
Apparently, most of the research that’s already been conducted looked at lesion-to-swallow-deficit relationship in much more broad and general terms. For example, if a patient just has oral and/or pharyngeal impairments based on where the lesion is, or if aspiration or residue symptoms are present based on lesion sites.
What makes this article different and jaw-dropping is how the authors looked at the specific physiological impairments of swallowing based off the 17 components from MBSImP standard protocol during MBSS, while in the brief, acute stages of stroke onset. Is this NOT on an acute SLP’s wish list?!
To identify the specific sites of lesions after these acute strokes, very specific and technical neuroimaging that I could only wish to one day see and understand (DW-MRI with whole-brain coverage to be exact) were used. Then, patients were to complete MBSS from their protocol in order to go back to the data and determine relationships between these 2 variables.
Something that we have to be sure not to skip over is that the neuroimaging medical experts who reviewed the images to determine just where exactly these patients’ lesions were were also blinded to any results from MBSS, thereby decreasing more bias in this area of the study (points scored for internal validity!!).
While most of us are somewhat familiar from at least hearing MBSImP being thrown around in conversations or social media posts, the article luckily provides a very short table summary of all the 17 components that MBSImP looks at. Along with all these separate components, there are a couple “Sums” or total scores for oral and pharyngeal swallow function. Yes, I know not every clinician is using this protocol and everyone has their own take. I remember it first becoming a “thing” and the ongoing rumors surrounding it. I will say I do like the idea of standardizing something that could potentially improve our clinical skills (versus merely guessing or being “emotionally” too involved, or, scared, in these instrumental assessments). The Penetration-Aspiration Score (PAS) was also used for risk of aspiration, “We calculated the worst and median PAS score across all performed swallows that were part of the standard protocol.”
The inter-rater reliability I supposed could always be greater to make a stronger study (aka 71.85%), however the authors did categorize “good agreement” as 0.4-75% compared to >75% as excellent agreement (probably driving all the Type A’s crazy🤪), so technically still in the clear.
Some other variables the authors considered during their analyses included:
- total lesion volume
- how many days went by from the neuroimaging to MBSS
- (that way they could argue the changes in swallow physiology impairment would not be due to these)
“Thus, with the lesion symptom mapping approach employed by this study, we attempted to elucidate the most critical brain regions for physiological swallow impairments, by modeling the impact of specific lesions locations on the severity of different swallow impairments.” p.3
Their initial results indicated that most of the lesions identified and located were involved from the middle cerebral artery (MCA) (ring a bell from all the chart reviews we see for this?) and in the right hemisphere, which apparently coincides with other studies claiming that the presence of more severe pharyngeal dysphagia is associated more in right-sided strokes. One specific alternative finding from this article was that some pharyngeal impairments (i.e. anterior hyoid movement, laryngeal vestibular closure) were found in the left hemisphere. This is a good thing to be aware of and further shows us that bilateral brain involvement is actually pretty crucial to the swallowing mechanism (it may just depend on how much of the sensorimotor parts are involved🤔).
Since there was a lot of missing or not enough data for all 17 components from MBSImP the authors were looking at–for example, not enough patients had been assessed during the MBSS with a solid bous to determine impairments in mastication, and not enough patients had been assessed in an anterior-posterior projection to determine pharyngeal contraction or esophageal clearance–the authors could only use 10 of the 18 components. They also had to narrow down the areas in the brain to supratentorial (supra-tentorial=cerebrum and brainstem😉).
So what did they have left?
“For four of the remaining 10 components, we found significant lesion-impairment relationships, these were laryngeal elevation, anterior hyoid excursion, laryngeal vestibular closure and pharyngeal residue.” p.6
Up till now it’s been so hard to not just quote every other paragraph because there is just SO much dang cool information that’s discussed in the article that will leave you🤯🤯! I tried my best to portray the general basis of their results and how they were interpreted in the table below (just the bare bones), but it definitely does NOT compare to the amazing image they actually provide you in the article!! (see bottom of post for the pretty version!)
As I’ve said, I’ve been a long lover of neuro since I was a wee undergrad student. Since anything involving the brain (and really, swallowing) can easily be over-explained and super complicated, instead of interpreting all the neuro terms and concepts, I decided to just stick with a few of what the authors stated and found. But seriously, this article is such an interesting review of a lot of neuroanatomy some of us learned many moons ago and easily meshes with how it relates to swallowing!!!
“Functionally, previous evidence suggests that the insula contributes to processing food taste, texture and temperature. In terms of swallow physiology, the insula has been associated with controlling the timing and synchronization of swallowing motor events by integrating sensory-motor information…Our findings present new information on the role of the insula in distinct mechanisms of airway protection during swallowing.” p.7
“Impaired laryngeal vestibular closure and pharyngeal residue were associated with lesions in the postcentral gyrus and impaired laryngeal elevation was associated with lesions in the precentral gyrus. These areas play a major role in decoding and encoding sensory-motor information and regulate the swallowing output of the brainstem through descending and ascending fiber tracts.” p.8
“Our study adds to the understanding of the role of the external capsule by showing a relationship between lesions in the external capsule and impaired laryngeal elevation and laryngeal vestibular closure.” p.9
Okay, that was all a lot to grasp (especially while trying to put these thoughts to writing!) in much fewer words than the article. And maybe I’m late getting on this bandwagon, but I actually had this article in mind recently when reviewing a chart for a new eval noticing more neuro terms like “peduncle” in there (trust me, all I wanted to do was re-read the article before the eval to remember the different brain area associations, but alas, #realworld😕). I’m definitely planning on keeping this article close to help with future insight with cases and to better marinate my neuro + dysphagia knowledge!
A couple caveats to consider before automatically working on laryngeal elevation whenever you see an insular infarction appear in your chart review…
First and most importantly, the authors admit they were missing quite a few data in matching regions with every single MBSImP component, and also hdidn’t ahve that much variability (essentially, they didn’t have enough participants with the same impacted regions). Additionally, at least from this study, we can’t have the same relationship pairings for the brainstem or cerebellum (although we can still base our hypotheses off other studies/neuroanatomy😉).
So does this mean every time we see a corona radiata stroke we automatically proclaim they have pharyngeal residue deficits? Well, no. But–we can use this information in conjunction with our cranial nerve and clinical bedside exams to further make hyptheses based on what we’re seeing (or not seeing) in order to make the most appropriate recommendations like direct visualization of the swallowing mechanism so we know what impairments to target!🤓
How can you use this article?!?
What a great talking point across clinicians or ice breaker with colleagues! What are your thoughts on mapping brain sites to not only dysphagia symptoms in general, but specific swallow dysfunctions??🤨
Or, do you feel this idea may be much more complex than this article could even begin to tap into, and there’s just way more things to consider??🤔
Why do you think this stuff is neat and could lead to a more specialized, neurologically driven field?!?🤓
For now, I am just patiently waiting and excited for more to come that can help us understand what to expect or why when it comes to stroke and site of lesions, and what to do about it in the treatment world. Unil then, if you need me, I’ll be burying my nose in that ‘ole Duffy textbook trying to figure all this external-capsule-fascicularus stuff out while eating a gyrus-shaped gyro🤤….
As promised here’s the awesome Figure 8. that’s provided in the article (prepare for your mind to get blown!!)
Article Referenced: [FREE ACCESS]
Wilmskoetter, J., Bonilha, L., Martin-Harris, B., Elm, J., Horn, J., & Bonilha, H. (2019). Mapping acute lesion locations to physiological swallow impairments after stroke. Neuroimage: Clinical, 22, 101685. doi: 10.1016/j.nicl.2019.101685