Assessment of Laryngopharyngeal Sensation in Adductor Spasmodic Dysphonia

Participant Recruitment Subjects with adductor type LD (AdLD) were identified and recruited by advertisements and by study clinicians at their institution. Advertisements were physically placed in the UCSF Voice and Swallowing Center clinic and were delivered electronically through the website of the National Spasmodic Dysphonia Association and to area LD ("spasmodic dysphonia") support groups.

Adults greater than 18 years old with AdLD were included if they received a diagnosis established by a multi-disciplinary evaluation by a fellowship-trained laryngologist and voice-specialized speech-language pathologist. Subjects diagnosed by a physician outside of the study facility were evaluated in-person by a fellowship-trained laryngologist to confirm their eligibility for this study. All patients were required to have history of favorable response to intra-laryngeal botulinum toxin A (BtxA) treatment, as further demonstration of the correct diagnosis of ADLD. This was especially helpful for patients initially diagnosed outside of our center. Subjects with abductor or mixed type LD were not included in the present study due to their low incidence, but concurrent essential tremor (ET) of the vocal tract was accepted.

Patients were also excluded if they had a history of: concurrent laryngeal diseases or conditions other than AdLD+/-ET; bleeding disorder or current anticoagulation use; head and neck radiation; active tobacco use; or drinking more than two alcoholic beverages per day. If laryngopharyngeal lesions and/or masses, impeding abnormal laryngopharyngeal structure(s), or excessive post-nasal drip were noted on laryngoscopy, then examination ceased, and patients were excluded. Prior to testing, subjects also completed symptom-specific patient reported outcome measures (PROMs), including: Reflux Symptom Index (RSI),18 Voice Handicap Index-10 (VHI-10),19 Dyspnea Index (DI),20 Cough Severity Index (CSI),21 and Eating Assessment Tool-10 (EAT-10).22 These PROMs are standardly collected as part of the routine clinical are for all patients undergoing evaluation at this center and are reported herein for holistic characterization of these subjects but not intended as a reflection or measure of the severity of their AdLD. Lastly, to avoid any potentially confounding physical effects from the injection (e.g., vocal fold edema), no testing was performed in the two weeks immediately following BtxA treatment. For patient convenience and to facilitate maximal enrollment, patients were allowed to undergo testing at any point outside of this post-injection window, although the majority pursued testing immediately prior to a BtxA injection on the same day.

Healthy controls were defined as adults between 18 and 85 years of age without laryngopharyngeal disease and were subject to the same screening and exclusion criteria.23 Additionally, controls were excluded if they had abnormal patient reported outcome measures (i.e. Reflux Symptom Index (RSI) score> 13, Eating Assessment Tool-10 (EAT-10) score>2, or Voice Handicap Index-10 (VHI-10) score> 11).

Aesthesiometer Device As outlined in previous work, modified nylon monofilaments fixed to the end of 5-French open lumen catheters were utilized to deliver tactile stimuli to laryngopharyngeal subsites.12 The Food and Drug Administration (FDA) has previously ruled the aesthesiometer to be a Nonsignificant Risk (NSR) Device Study (Q190371/S001). Three nylon monofilament sizes (6-0, 5-0, 4-0) were cut to a calibrated length of 30 mm to deliver three distinct tactile stimuli of increasing strength, known as buckling-force. The 6-0, 5-0, and 4-0 monofilaments deliver an increasing mean force of 0.03 g, 0.11 g, and 0.30 g, respectively.12 An intermediary strength "4.5-0" monofilament was created by using a 5-0 monofilament of 25mm length, which has been demonstrated to have a mean buckling force of 0.19 g.23 During testing, the monofilaments were passed through the working channel of a flexible ENF-VT2 laryngoscope (Olympus America, Inc., Center Valley, PA) to allow for direct visualization and concurrent stimulation of laryngopharyngeal subsites.

Laryngopharyngeal Sensory Evaluation All subjects underwent a standard protocol for laryngopharyngeal sensory evaluation. This has been described in detail previously but briefly reviewed again here.12,13 Prior to testing, subjects were screened for any recent changes in conditions affecting voice and swallowing to ascertain subjects-maintained inclusion criteria. Three investigators executed laryngopharyngeal testing: 1) one to operate the laryngoscope; 2) one to maneuver the aesthesiometer monofilament; and 3) one to monitor testing, record subjective patient response, and observe cough/gag/swallow responses.

An investigator then examined both nasal passageways with a nasal speculum, selecting the more patent pathway for laryngoscope insertion. The more patent nasal passageway was topically anesthetized with cottonoid pledgets soaked in a 50/50 mixture of 4% lidocaine hydrochloride and neosynephrine. The cottonoid pledgets were compressed to remove excess liquid to avoid unintentional spillage posteriorly to the nasopharynx and potentially larynx, and left in place for five minutes.

The channeled laryngoscope was then inserted along the inferior meatus towards the posterior nasopharyngeal wall. The 6-0 monofilament was pressed against the posterior nasopharyngeal wall and swiftly removed to establish a perceptual strength of "1". If subjects were insensate to this stimulation, monofilament size was incrementally increased (i.e., 5-0, 4.5-0, and 4-0) until the stimulus was perceived, to establish this internal anchor. As per the validated, standardized protocol, all AdLD participants were stimulated on the left, allowing maximal visualization of the vocal folds during testing due to camera configuration of the flexible laryngoscope. Only four controls were stimulated on the right side, during earliest phases of testing.

Starting with the 6-0 monofilament, the lateral pyriform sinus (LPS) was presented with the planned stimulus, followed by the aryepiglottic fold (AEF) and the false vocal folds (FVF). (Figure 1) Participants were instructed to raise their hand when the stimulus was detected, and then were asked by the study team to report a perceptual strength "score," in comparison to the nasopharyngeal anchor strength of 1. LAR response was observed and recorded by the study team. A negative response was defined as a lack of LAR to two appropriate stimuli. Gag or cough response to stimuli delivery were also recorded, assuming a positive LAR during these observations.

The LPS and AEF were tested in order of increasing stimulus: 5-0, 4.5-0 and 4-0 monofilaments. The false vocal folds (FVF) were tested last, in the same order of increasing monofilament strength. Testing of FVF terminated after the first observed LAR given site sensitivity, assuming positive responses would also be present for increased monofilament strength.

LAR Assessment Confirmation of LAR was determined using post-hoc frame-by-frame analysis of video recordings. Unilateral or bilateral vocal fold adduction following stimulus delivery was recorded as a positive response. Upon review, stimuli were excluded if they did not produce 10-30% monofilament buckling (as observed by the reviewer), were entrapped by saliva, or could not compress orthogonally to the mucosal surface. Additionally, if line of sight of visualization of vocal fold adduction was obstructed or confounded by phonation, the stimuli were excluded. All stimuli were reviewed by one study investigator with 30% of stimuli reviewed by a blinded second reviewer. Disagreements were reconciled by a blinded third reviewer.