Secrets of Neurolaryngology
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Secrets of Neurolaryngology LISTEN CAREFULLY JAMES P. THOMAS, M.D. LOOK CLOSELY VOICEDOCTOR.NET/NEURO Laryngeal Acoustic Testing - LCA paresis Clear sound Loud D5 Air leak Rough 2 seconds @ Diplophonia Vol ume B3 C5 Flutter Soft Male FemaleA3 Onset delay Typical vocal range Pitch break C2 C3 C4 C5 C6 Short segment Low Pitch High VOICEDOCTOR.NET/NEURO 1 SUMMARY 3 Neurolaryngology 4 Secrets 5 Principles & Assumptions 6 Visual exam 7 Branching structure of CN X Regrowth 22 8 Observing muscles 9 Observing motion Slow & Fast 10 Secrets — Tools of the Trade 11 Secrets — Observation — Taking time 12 CN X — Upper branches 13 CN X — Superior Laryngeal nerve Cricothyroid muscle 14 CN X — Recurrent Laryngeal nerve Posterior Cricoarytenoid muscle 15 CN X — Recurrent Laryngeal nerve Lateral Cricoarytenoid muscle 16 CN X — Recurrent Laryngeal nerve Thyroarytenoid muscle 17 Reinnervation after injury 18 Technique — inferring tension from oscillation 19 Technique — two complimentary 16 perspectives 20 Example Case – dyspnea Dyskinesia 22 Example Case – weakness LCA paresis 23 Example Case – weakness TA & LCA paresis 18 24 Vocal capabilities patterns James P. Thomas, MD 909 NW 18th Avenue Portland, OR 97209 - USA voicedoctor.net thomas@voicedoctor.net +1 503 341-2555 June 2019 edition NEUROLARYNGOLOGY 2 Neurolaryngology Becoming a neurologist of the larynx takes time to observe and reason about the functions of each muscle of the larynx. There are three muscles on each side of the laynx innervated by the recurrent laryngeal nerve and one muscle on each side innervated by the superior laryngeal nerve and one essentially midline muscle, so we could say there are 9 muscles of the larynx. If there is only a binary on and off possibility for each muscle duing function, then in theory we have a possibility of 92 possible configurations of the larynx or 81 different positions that the vocal cords could assume. Of course in practice there are less than this because the muscles usually work in harmony on either side of the larynx. However, after an injury, a muscle might just be weak and function partially, so now we have at least three possible configurations for each muscle. No innervation, partial innervation, complete innervation, so we could say 93 possible visual configurations of the larynx or 729 different configurations. The nerves supply to the larynx is very robust. After a nerve injury, nerves will typically regrow. In this process of regrowth, the wrong nerve could supply input to a muscle. The nerve for the PCA might go to the TA muscle leading to contraction at an inappropriate time. Now each muscle could have at least 4 states: no function, normal function, partial function, function at an inappropriate time. So now we have at least 94 or 6541 different possible configurations. This is certainly potentially very confusing. To simplify, the examiner benefits from a video recording over several cycles of a function, including respiration and then phonation. Reviewing the film slowly and repetitively, looking at one function repeatedly and comparing side to side a pattern will usually be discernable. The same film can be reviewed again looking at a different function or area of anatomy. Reviewing motion of different portions of the larynx separately will lead to an understanding of when the muscles, and hence nerves, are firing. You will have a visual understanding of the neurophysiology of the larynx. Here are a few secrets to winnowing the complexity of movement down to a specific diagnosis. VOICEDOCTOR.NET/NEURO 3 SECRETS Secrets of a neurolaryngeal examination Visual States Stable Observationallow movement to happen repetitively. ▶ paralysis isolate laryngeal functions. ▶ paresis ▶ crossed reinnervation Techniques Get close ▶ synkinesis ▶ FUNCTIONS topical anesthesia ▶ respiration ▶ dyskinesis ▶ doesn’t impair movement ▶ phonation Unstable ▶ tremor Observe▶ Respiration patience ▶ inspiration ▶ spasm ▶ sniff to stretch ▶ expiration ▶ lift arytenoids Mimic ▶ fixation ▶ scope between false cords Phonation ▶ high pitch ▶ two perspectives ▶ low pitch then ▶ high pressure/flow/volume ▶ low pressure/flow/volume Visual diagnosis of laryngeal neurologic impairments is not only possible, but is the most accurate method for evaluating the neurologic status of the upper airway. findings▶ Atrophy - TA, PCA, False cord Tools▶ Video endoscope ▶ Fasciculation - TA body, PCA body, LCA arytenoid ▶ Digital recording ▶ Motion ▶ Topical anesthesia ▶ Range of rotation - LCA, PCA (joint, scar) ▶ Close exam ▶ Lengthening - CT (SLN, joint, scar) ▶ Vocal manipulation ▶ Oscillation - TA, CT ▶ Hyperactivation - LCA EMGAlthough EMG (electromyography) is commonly spoken of as the “gold standard” (if there even is one), visual examination offers a great deal - let’s say a platinum standard. NEUROLARYNGOLOGY 4 PRINCIPLES Assumptions Muscle▶ each muscle has action only a single action, ▶ that action can be isolated, ▶ that action can be elicited and visualized. Timing▶ each muscle has an appropriate time to contract, ▶ timing can be compared to the opposite side, ▶ timing can be compared to expected function, ▶ inappropriate timing represents reinnervation by an opposing nerve branch. Compensation▶ the patient always attempts to compensate, ▶ removing compensation reveals pathology. VOICEDOCTOR.NET/NEURO 5 VISUALIZING Neurolaryngology: VISUAL EXAM Careful listening & close observation are more precise neurolaryngeal diagnostic methods than laryngeal EMG. NEUROLARYNGOLOGY 6 INTRODUCTION The branching tree structure of the nerve he first step in visual neuro- first location is where the 10th cranial nerve only single branch of the nerve is involved, we laryngology is for the examiner leaves the skull and heads towards the neck. know the injury is taking place very near to the to have a mental map of laryn- It passes through a very narrow opening along larynx. If multiple branches are involved, we geal anatomy. Understanding the with two other cranial nerves, the XIth and know the injury is taking place further away treelike branching of the laryn- the XIIth cranial nerves. From a diagnostic from the larynx and closer to the brain. geal nerves will allow us to work perspective, this bottleneck then is a location The extended path of the left recurrent Tboth forwards and backwards from clinical where an injury to the nerve will likely affect laryngeal branch of the Xth cranial nerve de- information we have. If we know where and not only the Xth cranial nerve but also the XIth scending into the chest and wrapping around how an injury took place along the path of the and the XIIth cranial nerves. So in our endo- the aorta and left bronchus while the right nerve, then we will know the findings and im- scopic upper airway examination, if there are typically remains recurrent in the lower neck pairments that we should see on an endosco- problems with the tongue (XIIth cranial nerve) is one of the most well known diagnostic asym- pic examination. Likewise we can work in the or with lifting the arm and shoulder up (XIth metries. reverse direction. Based on the functional im- cranial nerve), in addition to problems in the Since speech and voice overlap in function, pairments that are seen on an endoscopic exa- larynx, we will know to focus our attention on assessment of the tongue, soft palate muscles mination, we should be able to predict where this narrow opening at the base of the skull. and pharyngeal constrictors contribute to un- along the path of the nerve the injury took or The second diagnostically important loca- derstanding laryngeal neurologic injury. is taking place. tion is where the Xth cranial nerve descends in The larynx is supplied by the Xth cranial the neck, it gives off four branches to supply nerve, the vagus nerve. There are two import- the throat and larynx. Knowing which of these ant anatomic locations along the path of this branches are affected, will tell us how high nerve for the examiner to think about. The the location of the injury is in the neck. If INTRODUCTION Regrowth second principle of neurolaryn- gology is that the Xth cranial BILATERALIn many injuries of SYMMETRY the larynx, we have a nerve, when injured, almost built in reference point. When one laryngeal always tends to regrow and nerve is injured, the other side continues to supply muscles with nerve function normally and provides the examiner input. Mild injuries and injuries with a direct comparison by way of asymme- closeA to an individual branch of the nerve will try in anatomy and function between the two tend to recover with normal function. sides. We can compare the structure on the left More severe injuries and more proximal with the structure on the right. We can also injuries, that is, injuries that are closer to the compare the timing and range of movement main trunk of the nerve, will result in regrowth on one side with the other. with crossing of nerve pathways to different branches. This will result in various degrees of mixed up functioning of the muscles of the larynx. Even in cases where there is a gap between the cut ends of the nerve, the cut neurons will often gradually grow through the intervening tissue and reconnect with the denervated muscles. VOICEDOCTOR.NET/NEURO 7 OBSERVING Muscles Some of the muscles innervated by the laryngeal nerves are so close to the surface mucosa that they can be nearly directly visualized. Others are deeper and only their effects can be visu- alized. Near direct visualization includes the ability to see the muscle contract and thicken