2018 Section 6 - Laryngology, Voice Disorders, and Bronchoesophalogy

L ARYNGEAL EXAMINATION IN THYROID AND PARATHYROID SURGERY

the stroboscopic motion picture; high-speed imaging pro- vides a clear advantage in that it can be used in the set- ting of aperiodic vibration. 34,41 It remains, however, an imperfect tool as it generates extraordinarily large vol- umes of data per examination. An EMG records changes in electrical potential within muscles. The clinical utility of laryngeal EMG is controversial, because of a dearth of objective clinical evidence. In 2009, an expert panel sup- ported the use of laryngeal EMG in guiding injections of botulinum toxin in laryngeal muscles and in the diagnosis of laryngeal movement disorders. Laryngeal EMG can detect nerve injury, synkinetic activity, myopathy, and the innervation status of a muscle. It can also differentiate between central and peripheral disorders. Laryngeal EMG is usually performed percutaneously and the most frequently sampled muscle is the thyroartenoid. To access this muscle, straight needle electrodes are most commonly used. These are inserted through the cricothy- roid membrane and directed upward. To reach the posterior cricoarytenoid muscle, the larynx is rotated away from the side to be sampled. Alternatively, the needle is passed through the cricothyroid membrane, across the airway, and through the cricoid cartilage. To access the cricothyroid muscle when investigating possible EBSLN palsy, the nee- dle enters the midline over the cricoid cartilage and is then directed laterally over the surface of the cartilage. Neck flexion is required to confirm that the electrode is not in a strap muscle. For all techniques, insertion or movement of the electrode causes a brief electrical burst, termed “insertional activity,” and voluntary muscle contraction results in an “interference pattern,” which represents the combined signal resulting from the multiple action poten- tials from individual motor units. When using EMG to investigate possible neural injury after thyroid and parathyroid surgery, an incomplete nerve injury or incomplete regeneration results in a diminished “picket fence” EMG pattern. With complete nerve disrup- tion, there is initially no voluntary muscle activity, how- ever, over time, spontaneous fibrillation potentials and positive waves begin to occur. If axons regenerate, they are not directed to the same muscle fibers that they sup- plied before the injury and tend to supply clumps of muscles and to connect to more fibers than in a normally innervated muscle. Thus, action potentials become “polyphasic” with greater amplitude and more “turns.” These polyphasic potentials are evidence of nerve dam- age. Complete electrical silence in a laryngeal muscle has been correlated with a poor prognosis for recovery of an immobile vocal fold. Laryngeal EMG remains a qualitative, not quantitative tool. Some clinicians report the percentage of denervation in a muscle based on a subjective assessment of the inter- ference pattern. However, the EMG signal varies greatly depending on the impedance of the electrode, its position within the muscle, and the degree of effort expended by the subject. Turns analysis, which quantitatively measures motor unit activation and recruitment, holds promise as a quantitative measure of abnormal reinnervation, but fur- ther research is required for validation. Laryngeal electromyography.

the examination chair. Topical anesthesia is not usually required except in patients with strong gag reflexes. The patient’s tongue is grasped with gauze by the examiner and retracted anteriorly and the camera is gently advanced into the oral cavity to the level of the soft pal- ate. The patient is instructed to say “eee” while the cam- era is further advanced and/or rotated until adequate images of the larynx are obtained. These images are eval- uated for symmetry, periodicity, mucosal wave, amplitude of vibration, glottic closure pattern, and the shape and contour of the vocal fold free edge. 33,35 Periodicity describes the regularity of the vibratory cycles of the vocal folds, a feature important with regard to both iden- tification of pathology (normal vocal folds are expected to have consistent, periodic vibratory cycles) and techni- cal consideration (poor periodicity may prohibit useful synchronization of the strobe light and thereby limit its diagnostic utility). 33 Stroboscopy is beneficial in the diagnosis of mucosal vocal fold abnormalities, including nodules, polyps, cysts, scar/sulcus, atrophy, subtle epithelial neoplasms, and path- ologic anterior or posterior glottic gaps. With regard to use of a stroboscopy in thyroid disease, stroboscopy is not required to identify an obviously immobile or paralyzed vocal fold. However, identification of subtle hypomobility or paresis (incomplete paralysis) is aided using this tech- nique. In paresis, common stroboscopic findings include vocal fold bowing (70%), incomplete closure (62%), and increased vibratory amplitude (38%). 36 Stroboscopy may also show subtle findings associated with vocal cord dys- function, including false vocal fold hyperfunction on the side contralateral to the weak vocal fold and mismatch of the interarytenoid spatial relationship of the vocal proc- esses. Such subtle stroboscopic observations may be impor- tant in determining exact treatment options most beneficial for a given patient. One survey of laryngologists suggests that 72% rely on stroboscopy to diagnose vocal fold pare- sis, favoring it over other forms of laryngoscopy and laryn- geal electromyography. 37 Isolated superior laryngeal nerve paresis may also be informed by stroboscopic examination producing vocal fold bowing and shortening, vocal process height asymmetry with the ipsilateral vocal process over- riding the normal contralateral side, and ipsilateral hyper- adduction of the false vocal fold. 38 The technique has certain limitations and should be avoided in cases in which impaired periodicity may make synchronization with the strobe light problematic. 34,35,39 Furthermore, its interpretation is subjective; there is not an established measurement tool with demonstrated inter- rater reliability, internal consistency, and discriminant validity. 34,40 Thus, comparisons or pooling data at a national and international level may be difficult because of heterogeneity in the collection and measurement sys- tems as well as the diagnostic terminology. Stroboscopy is not the only technique available for a detailed evalua- tion of laryngeal movement and pathology; others include electroglottography, videokymography, and high-speed digital imaging, and some techniques may be complemen- tary. 34 High-speed digital processing has the advantage of capturing images as often as 5000 frames per second, acquiring many images from within a single glottic cycle, rather than relying on the multiple cycles that constitute

HEAD & NECK—DOI 10.1002/HED JUNE 2016

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