Sulcus vocalis in spasmodic dysphonia-A retrospective study.

Background: Spasmodic dysphonia (SD) is a neurological condition of the larynx characterised by task specific, involuntary spasms of the intrinsic laryngeal muscles causing frequent voice breaks during speech. The current treatment modality involves Botulinum Toxin injections into the affected group of muscles. This has yielded satisfactory results in Adductor SD (ADSD) and mixed SD but not in Abductor SD (ABSD). Sulcus vocalis is a morphological condition of the vocal folds with invagination of the superficial epithelium into the lamina propria or deeper layers. It is characterised by breathiness in voice and hypophonia. In our voice clinic, patients diagnosed with SD were occasionally found to have a sulcus on flexible stroboscopy. Studies have revealed an asymmetric stimulation of both the adductor and abductor group of muscles in ABSD and a predominant possibly symmetric stimulation of the adductor group of muscles in ADSD. Our objective was to study any significant association between vocal fold sulcus and two groups within SD; group one being ADSD and group two being both ABSD and Mixed SD. A literature review did not reveal any studies suggesting an association between SD and vocal fold sulcus to date.

Methods: A retrospective review of the stroboscopic video recordings as well as file records of all patients diagnosed with SD between January 2016 and September 2019 was conducted at our voice clinic. The first author was the laryngologist who had diagnosed SD and its type on the basis of hearing the voice and making the patient perform various vocal tasks with and without flexible videostroboscopy. The SD patients were divided into two groups with the first group consisting of ADSD patients and the second group consisting of ABSD as well as Mixed SD patients. The presence or absence of vocal fold sulcus was noted in all the SD patients. Odds ratio was used to establish statistical significance of the presence of vocal fold sulcus in the two SD groups.

Results: Among the 106 patients of SD, 62 patients were males and 44 were females. A total of 84 patients were diagnosed as ADSD, 10 as ABSD and 12 as Mixed SD patients. Vocal fold sulcus was noted in 5 out of 84 patients of ADSD, 4 out of 10 patients of ABSD, and in 3 out of 12 patients of mixed SD. Odds Ratio of 7.37 (C.I. = 2.063-26.35) was obtained for the second group of patients i.e. ABSD and Mixed SD.

Conclusion: Our study revealed a significant association between patients of SD having an abductor component (ABSD and mixed SD) and vocal fold sulcus. The two hypothesis proposed for this are the possibility of asymmetrical adductor and abductor muscle stimulation in SD being responsible for the development of a vocal fold sulcus or the primary presence of a vocal fold sulcus contributing to altered sensory feedback resulting in SD. Further study to evaluate this, as well as a study of the vocal response to medialisation procedures for patients of ABSD with sulcus is recommended.