Title: Mapping acute lesion locations to physiological swallow impairments after stroke
Author: Wilmskoetter, Bonilha, L., Martin-Harris, Elm, Horn, & Bonilha, H.
Journal: NeuroImage: Clinical
Year of Publication: 2019
Study design: 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
Remember your undergraduate and/or graduate neuroanatomy course? I know some loathed is and some loved it. For me, I was so 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 for sure had my share of experience within this realm, reading this article brought me back to my first love, while also mixing in my new 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 makes up this huge amazing network when it’s all put together. This automatically brought me back to my #1 fave movie Ferris Bueller’s Day Off (check it out kids 😉 ) at the musuem looking at the famously layered pointillism painting “A Sunday Afternoon on the Island of La Grande Jatte.”
We’re still working as a field to try to begin to understand how all these parts work together to form a nice, 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 (fyi after a quick Google search, supra-tentorial just means cerebrum). 😀
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/residue symptoms are present based on lesion sites (based off clinical bedside exams or FEES).
What this article’s authors looked at were 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. 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, understand, or nerd-out about (DW-MRI with whole-brain coverage to be exact) was used. Then patients were to complete MBSS from that protocol in order to go back to the data and determine relationships between these 2 variables.
A quick note I’d like to highlight is that the neuroimaging medical experts who reviewed the images to determine just where exactly these patients’ lesions were were blinded to any results from MBSS, which decreases any bias in this area of the study (points scored for internal validity!!).
While most of us are somewhat familiar from at least hearing the term “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, so I admit it’s definitely on my list of things to do soon! 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 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.”
Unfortunately, the inter-rater reliability I supposed could have been greater to make the study stronger (aka 71.85%, however the authors did categorize “good agreement” as 0.4-75%, compared to >75% as excellent agreement).
Some other variables the authors considered during their analyses included age, total lesion volume, and how many days went by from the neuroimaging to MBSS (in order to argue the changes in swallow physiology impairment would not be due to these). (See full article for specific patient demographics).
“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 this in?), as well as most of the significant areas of lesions of interest were found in the right hemisphere, which apparently coincides with other studies claiming that the presence or more severe pharyngeal dysphagia is associated more in right-sided strokes. One specific alternative finding from this article was that some pharyngeal impairments (anterior hyoid movement, laryngeal vestibular closure) were found in the left hemisphere. This is actually NOT a bad thing, 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 (in other words, not enough patients had lesions in the same areas, or not enough patients had enough lesions across different locations for variability), the authors could only use 10 of the 17 components. They also had to narrow things down after not being able to include or find any significance for the oral/pharyngeal total sum scores. 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 I’ve been holding off on the direct quotes so far because there is just so much dang cool information that’s discussed in the article! 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)
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 we learned many moons ago, and easily meshes with how it relates to swallowing, so a super recommended read none the less!!!
“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 (as well as inerpret in my head while writing this!) 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 and actually finding 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 my marinate my neuro + dysphagia knowledge!
How can you use this article?!?
I also think this article can be a great talking point across clinicians and maybe even an interesting topic to bring up in any journal clubs! 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. So if you need me, you’ll find me 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 cool Figure 8. that’s provided in the article (prepare for your mind to get blown!!)
- “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…it is believed that the external capsule is a critical link between cortical motor regions and the basal ganglia and contributes to the engagement of the basal ganglia in motor control”
- “Thus, it may be that damage to the supramarginal gyrus or the superior longitudinal fasciculus disrupts the input from the parietal sensory-motor brain regions to the frontal motor-coordination and motor-initiation areas”
- “We found a significant association between lesions in the thalamus and impaired anterior hyoid excursion. Further, we identified the amygdala…to contribute to impaired anterior hyoid excursion.”
- “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…Our study emphasizes the importance of afferent sensory information for swallowing safety.”
Article Referenced: [FREE ACCESS]
Wilmskoetter, Janina, et al. “Mapping Acute Lesion Locations to Physiological Swallow Impairments after Stroke.” NeuroImage: Clinical, vol. 22, 2019, p. 101685., doi:10.1016/j.nicl.2019.101685.