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Why the F @$% do we need to know about these stupid @$$ cranial nerves (CNs)?
I know, this post may seem so lame and elementary to some SLPs, but to others, if you’re anything like I was when I first got out of grad school and started working with patients with dysphagia, any sort of neuroanything gave me a major case of the dumbs.
I’ve come across a few SLPs in my mobile FEES (Fiberoptic Endoscopic Evaluation of Swallowing) practice lately that have no concept of the importance of the cranial nerves. I started asking around to a few SLPs to see if they are doing a CN exam in their initial clinical swallow exam (CSE) and I got a pretty shocking response from ALL of them! NO!! At first I was like WTF?!? How could you not?!?! THERE’S SOOO MUCH VALUABLE INFO THERE! But then I remembered when I first started out working in skilled nursing, I really had no clue how to do one properly or how it really could help me with my patients either! I took plenty of CEU courses to bring my knowledge up to par, but I know time and financial constraints sometimes don’t allow us to take ALL the courses, so I thought I’d share what I know.
Now obviously since I do FEES for a living, I feel very strongly about the importance of instrumentation, but I also know some administrators are not willing to get with 2017 and see the value of an instrumental assessment. Therefore, some SLPs are left to get by with what info they have, and the longer I’m in this profession, I see SLPs trying to get by with little to no information. That’s just not cool kids! Some aren’t even doing chart reviews! Just hearing from a passerby that Maggie Sue is choking on her food, stare at her in the dining room for 45 minutes, make the executive decision that she’d be better on honey thick liquids, and meanwhile the patient and her family are flipping absolute shit! No! No! and no!! (And if you think I’m lying, I’m sorry to report this really is the sad state of affairs at some SNFs).
I also do believe that some SLPs have almost dumbed themselves down to that level, and really have no concept of how powerful our profession truly is, and how you really can improve the swallow! Not just watching and downgrading, but actually intervening and improving! What a concept! If you’ve been one of these people, you don’t have to raise your hand, just channel your inner Maya Angelou and once you know better, you do better!
In order to spare you a case of the dumbs, or spiral you in to neuroanatomy-induced alcoholism, I’m going to break this down, and I’m going to discuss 1 cranial nerve at a time. I’m going to talk about what it does, how to asses it, and how it can help to determine your treatment.
DAY 1 – TRIGEMINAL WHOOP WHOOP!!!!
The trigeminal nerve is cranial nerve 5! Yes, FIVE! CINCO! In roman numerals it looks like a V, but yes, its 5. CN V is innervated by the trigeminal motor nucleus and V3 – the mandibular branch. (There are 2 other branches, V1 and V2, but I promised to keep the “dumbs” at a minimum). The mandibular branch provides both sensory inputs (from the peripheral nervous system (PNS) to the central nervous system(CNS)) and motor outputs (from the CNS to the PNS).
CN V has sensory inputs (meaning feeling) as in if you tickle my nose, I will or won’t feel it. The trigeminal nerve controls all somatosensation (aka touch, pain, and temperature) to the face and anterior 2/3 of the tongue. (I know its tricky because you’d think the facial nerve should get on that, but nope!) So tell the patient to close their eyes, you can lightly touch the tip of their nose with a q-tip and if they can feel it voila! Sensory portion of trigeminal works! (The trigeminal nerve also provides some sensory innervation to the soft palate, but just tuck that info in your cranial nerve back pocket.)
Side note: Feeling of pain and temperature sensation in the face require innervation from the lateral medulla. Lack of such can be a sign of a potential medullary infarct, or a part of Wallenberg Syndrome. Imagine if you were that guy that caught that! How cool would you be?!? (Thanks so much Karen Sheffler of swallowstudy.com for that contribution!)
I always remember the trigeminal being a tricky one because it controls 3 separate unrelated entities, that actually end up all being related! Weird! The trigeminal nerve is responsible for the motor movement of the TENSOR veli palatini, the muscles of mastication, and the suprahyoid laryngeal muscles (meaning lift up the hyoid, aka supra important for swallowing!)
It has been thought by other professionals in our field that the tensor veli palatini is responsible for tensing the velum. However, it has been determined that it really couldn’t, and certainly can’t elevate it! The tensor veli palatini is responsible for opening the eustacian tube. (Thanks Dr. Kate Krival for straightening that out for me!)
I stumbled upon an awesome mnemonic on Wikipedia for remembering the muscles that the trigeminal nerve innervates:
MY TENSORS DIG ANTS 4 MOM
MYlohyoid + TENSOR veli palatini + DIGastric (ANTerior) + 4 Muscles Of Mastication (masseter, temporalis, medial and lateral pterygoids).
Alright, now how do we assess these bad boys?
To assess the muscles of mastication, have the patient clench their cheeks, if you feel the bulging at the jawline, Yahtzee! After clenching of the teeth, have them open their jaw, if there is a deficit, the jaw will deviate to the weak side.
To assess the suprahyoid muscles, gently touch the patient’s hyoid bone, ask them to swallow, and feel for hyolaryngeal elevation. Very minimal to no elevation can indicate an impairment here, but it is a very rough guide. You can also put your hand under their jaw and ask them to tense their lower jaw muscles to feel for the ability to tense the floor of the mouth, hence roughly assessing the mylohyoid.
Now, If ANY of these deficits are present, then you know we have some sort of motor trigeminal nerve (CNV3) involvement going on. Obviously an instrumental assessment of a modified barium swallow study (MBSS) or FEES would be ideal, but if you find a deficit in any of these areas, you know to put your headlights on! It could mean a deficit in the oral phase with poor mastication, oral transfer with poor stabilization of the floor of the mouth, AND/OR the pharyngeal phase with decreased hyolaryngeal excursion (which we know is a huge predictor in dysphagia)!
If you know the patient has an injury to one side or the other, allow that to tailor your treatment! Perhaps a head turn, or head rotation to the weak side will allow for the unaffected, stronger side to lead the way! We also can try the Mendlesohn, Shaker, or CTAR (barring any contraindications) since you know they may have some difficulty with hyolaryngeal excursion. NMES or EMST are possibilities as well.
Do NOT be afraid to try something new, and dig a little deeper! Sometimes we have to work with what we have, and we all have something!
Corbin-Lewis, K, Liss, J.M., & Sciortino, K.L., 2005, Clinical Anatomy & Physiology of the Swallow Mechanism, Thomson Delmar Learning, Clifton Park, NY
Murray, J., 1999, Manual of Dysphagia Assessment in Adults, Singular Publishing Group, Inc., San Diego
Mnemonic device: https://en.wikipedia.org/wiki/Trigeminal_nerve