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patients with horizontal and vertical tremor underwent initial TA injections that were converted to TA+S injec tions, and two of these three patients demonstrated improved subjective scores. A prospective study could also further explore and characterize the addition of strap muscle injections in this patient group. To our knowledge, this study is the fi rst to quantita tively demonstrate improvement in outcomes with tar geted strap muscle injection. The 2013 paradigm study did report patient improvement; however, quantitative scoring was not provided. 4 It is worth noting their proto col differed from ours in that they alternated thyroaryte noid and strap muscle injections to avoid signi fi cant dysphagia, whereas we performed concurrent injections. Additionally, our botulinum toxin dosage range was 2 to 3 units on each side, whereas theirs began at 2.5 to 5 units, and our strap injection technique did vary slightly from theirs. In our patient population, we did not fi nd a prohibitive degree of dysphagia, nor did dysphagia rates increase in a clinically signi fi cant way when strap muscle injections were performed (16.0% vs. 16.6%). In our study, strap muscle injections only occurred over the thyroid lamina in an infrahyoid location; we did not per form suprahyoid injections. Another recent and large study extensively compared LBTX outcomes among VT, and adductor and abductor spasmodic dysphonia patients. 6 Although they did consider vertical and hori zontal tremor components, strap muscle injection was not included in their study. The authors acknowledge that vertical tremor is likely a multifactorial process, caused by tremor in a variety of extralaryngeal musculature, and may not be isolated to the strap muscles. Several of our patients did exhibit tremor in other sites as well. How ever, due to dif fi culty in identifying the origination of the vertical tremor with certainty, and the concern for prob lematic dysphagia by injection suprahyoid and pharyn geal musculature, we feel that infrahyoid strap muscles are a pragmatic target for therapy. Due to their accessi bility and lack of need for a laryngoscope or EMG, they are a reasonable empiric therapy target site for vertical tremor, and our data suggest reasonable outcomes with this approach. Other muscles, such as cricothyroid or interarytenoid, were not the focus of our study; however, they could be considered in future investigations. Limitations of our study include its retrospective nature. Botulinum toxin injection is well known to pro vide a temporary effect. One review of LBTX for spas modic dysphonia described a duration of effect from 14 to 18 weeks, 12 and other studies have suggested 10 to 17 weeks depending on botulinum toxin subtype. 5 These reports are consistent with our patient-reported outcomes of 12.8 weeks. Injections are planned to provide patients a steady state of bene fi t, and are intentionally timed to occur as the bene fi ts of LBTX are beginning to wane. Because our outcomes data were measured at each injec tion, our average follow-up time was approximately 17 weeks, and in some cases longer. Although not ideal, this follow-up duration represents the real-time dif fi culty by both surgeon and patient to appropriately time injec tion with physician, patient, and LBTX clinic availability. Additionally, many of our patients did remark on

TABLE III. Patients With Horizontal and Vertical Tremor Who Underwent Both TA and TA+S Injections.

Mean Subjective Improvement Score

Patient No.

No. of Injections

Mean Δ VHI

Mean Δ CAPE-V

Location

− 7 − 4

4

TA

1 2 2 1 1 8

50% 83%

0

− 5

TA+S

6

TA

13% 0.5 15% 4 50% 0

0 0

TA+S

− 30 − 15

16

TA

− 0.6

TA+S

78%

Mean outcomes of both methods are shown. CAPE-V = Consensus Auditory Perceptual Evaluation of Voice; TA = thyroarytenoid; TA+S = thyroarytenoid and strap muscle; VHI = Voice Hand icap Index.

options may be limited due to lack of bene fi t from medi cal management in many patients. Though tremor of the larynx can involve both horizontal and vertical com ponents, traditionally only the horizontal components have been treated with LBTX to the adductor compart ment of the vocal folds. In 2013, investigators proposed a new paradigm for management of vocal tremor, involving the characterization of tremor into vertical, horizontal, or a combination of the two, and described injection of the strap muscles with botulinum toxin to address the vertical contribution. 4 To date, outcomes of this approach are not well described in the literature. Herein, we report on our experience with botulinum toxin injection to the strap muscles, in addition to thyr oarytenoid muscles, using patient-reported and vocal perceptual data. Results of our study suggest meaningful improvement in subjective voice outcomes with LBTX, with 98% of injec tions showing some bene fi t, and a patient-reported subjec tive improvement score of 70% per injection. Furthermore, TA+S injection improved outcomes in patients with both vertical and horizontal tremor compared to TA injection alone. Patients in this group who received TA+S injections show a statistically signi fi cant improvement in their sub jective improvement score (74% vs. 35%, P < .005). In regard to CAPE-V subscores, only in the categories of breathiness and pitch did the TA+S injection group have a less negative change in score, suggesting that this group had worsening of their pitch and increased breathiness compared to the TA-only group. One explanation for this is that pitch changes were a side effect of LBTX with decreased function of the TA muscle, and thus more pro nounced in the group that also had greater bene fi cial effects. Similarly, CAPE-V roughness and loudness scores increased for both groups, which also may be a product of LBTX side effects (Table II). Further studies, ideally in a prospective environment, where patients could be evalu ated at the time of peak vocal bene fi t would enhance the validity of the CAPE-V and VHI data. Laryngovideostrobo scopic data could also be reported. Additionally, intrapatient analysis also supported utility of TA+S injections in a small subgroup. Three

Laryngoscope 129: June 2019

Nelson et al.: Strap Muscle Injections for Vocal Tremor

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