Unilateral vocal fold paralysis (UVFP) may present as dysphonia, loss of the upper register of the voice, hoarseness, breathiness, throat pain, choking episodes or decreased vocal stamina.1–5 Patients with UVFP may demonstrate different degrees of voice perturbation depending on the position of the paralyzed vocal fold.6–8

Treatment of unilateral vocal fold paralysis is designed to eliminate aspiration and improve quality of the voice. Different surgical techniques are available today: teflon, collagen, hydroxiapatite or autogenous micronized dermis, fat injection, type I thyroplasty and nerve muscle pedicle transfer represent the surgical techniques mainly adopted. These studies conduct evaluations mostly in the immediate post-surgery period and three months after surgery.9–18

Only three studies have evaluated voice therapy efficacy for this population. Schindler et al.19 analyzed retrospectively voice modifications in 40 patients with UVFP from different etiologies before and after voice therapy. A multidimensional assessment protocol was used and it included videoendoscopy, the maximum phonation time (MPT), the GRBASI scale, spectrograms, perturbation analysis and the voice handicap index (VHI). Pre and post early treatment data were compared. A complete glottal closure was seen in 8 patients before voice therapy and in 14 afterwards. Mean MPT increased significantly. In the perceptual assessment, the difference was significant for five out of six parameters and a significant improvement on quality of life was also reached. D’Alatri et al.20 evaluated the laryngological and acoustical results obtained after voice therapy in 8 patients with UVFP caused by different etiologies. After behavioral therapy, the prevalence of complete glottal closure increased significantly (p<0.05). Subjects’ pre-therapy mean values for Jitter, Shimmer and noise-to-harmonic ratio were significantly different from those taken both immediately and 6 months after treatment (p<0.05). Mattioli et al.21 conducted a 7 years prospective study to evaluate the post vocal early treatment results of 74 patients with UVFP. Patients underwent multidimensional assessment pre and post treatment and the results shown that 51 (68.9%) patients recovered vocal fold mobility, and 23 (31.1%) had persistent paralysis after voice therapy. In this group of patients, complete glottal closure was observed in 5 cases before the voice therapy, and in 13 patients this complete closure was observed only after the therapeutic process (p<0.0001). An important and significant reduction in fundamental frequency was found (p<0.0001); an improvement was seen for the mean values of Jitter (Jitt%; p=0.001), Shimmer (Shim%; p<0.0001) and noise-to-harmonic ratio (NHR) (p<0.0001). Voice handicap index (VHI) values showed a clear and significant improvement and mean MPT increased significantly.

At this time, there are no studies that report the risk factors for vocal improvement after voice therapy. Although there are three previous studies demonstrating the efficacy of voice therapy for patients with UVFP, there are no multidimensional studies that evaluate the long term.

Understanding the effectiveness of voice therapy in this population may be an important coefficient to define the therapeutic approach. Voice therapy is the noninvasive intervention and an understand of factors listed above is essential for adequate indication. This is the first study that evaluated the voice therapy effectiveness for short, medium and long term in oncological patients with UVFP and that determine the risk factors for voice rehabilitation failure.

From the 28 patients with permanent UVFP, 18 (69.2%) presented with complete glottal closure following voice therapy (p=0.001).

Perceptive auditory analysis comparisons pre and post therapy (short, medium and long term) revealed a significant difference between the four evaluation time points for most parameters (overall dysphonia degree, roughness, breathiness, instability, maximum phonation time, loudness and pitch) (Table 1). The multiple comparisons for the GRBASI scale revealed significant differences at the different evaluation time points, except between the medium and long term time points (p<0.005). The data suggests that there was a voice improvement over time with stabilization of the results after 6 months (medium term).

The acoustic results showed improvement presented in the different stages of evaluation (pre, short, medium and long term) (Table 2). The variables that displayed significant differences were PPQ and Shimmer, which were decreased if compared to baseline. On the acoustic analysis, there were significant differences when comparing overall improvement and partial improvement for Jitter (p=0.016) and PPQ (p=0.006) parameters (Table 3).

Comparisons of variables related to VHI questionnaire over time also displayed significant differences for all variables. For the overall score, there was a difference pre therapy compared with other time points (values were, on average, higher than at other time points) (Table 4).

Table 5 presents the results of the logistic regression used to determine the risk factors for non-improvement. The results indicated that Jitter entered the final model as a risk factor for partial improvement. For every unit of increased Jitter, there was an increase of 0.1% (1.001) of the patient chance for partial improvement, which indicates an increase in the no full improvement chance during rehabilitation.

Some studies demonstrate the effectiveness of voice therapy rehabilitation for UVFP.19–34 The present study confirms the voice improvement for medium and long term rehabilitation.

The variables pitch, loudness and MPT also displayed improvement when comparing previous and immediately post therapy evaluation results; however, when comparing the results at the medium and long term evaluations, the differences were not significant. These data show that the results achieved during therapy were maintained over time, but without progressive improvement after 6 months, suggesting vocal quality stabilization.

Acoustic analysis results (PPQ and Shimmer) indicated improvement over time. These values were on average lower in the short, medium and long term when compared to the initial assessment.

In cases with continuing permanent vocal fold paralysis, glottal closure improvement became complete in most of the patients when compared with the initial otorhinolaryngology evaluation. The presented data is consistent with other studies that have evaluated the voice rehabilitation effectiveness. Different factors are involved in glottis closure. For example, interarytenoid musculature and cricothyroid muscle action can also help in the vocal fold medial movement and finally the inferior pharyngeal constrictor muscle, which can also help glottal closure. Based on the results found after voice therapy, we suggest that all of these settings can be favored by the techniques used during speech rehabilitation.

The consulted literature did not present data defining risk factors for unsatisfactory development in voice therapy in patients with unilateral vocal fold paralysis. The sample characteristics were similar in the groups with total and partial improvement. The auditory perceptual evaluation results, otorhinolaryngology evaluation and VHI had no significant differences.

In this study, the acoustic measures were the only factor directly related to UVFP patient improvement. The literature data suggest that voice disorder analysis, besides being an easy procedure, can indirectly and noninvasively measure laryngeal function and determine the vocal fold vibration condition.35

The Jitter and Shimmer parameters are widely used in scientific and clinical performance to predict diagnoses, as well as to document and evaluate dysphonia treatment.36–38 Different authors suggest that Jitter and Shimmer can be important predictors for changes on laryngeal physiology diagnosis.39,40 However, there is controversy regarding Jitter and Shimmer analysis because of low reliability, sensitivity and specificity when voices with high roughness, low pitch and aperiodic signal are evaluated.41

In the study sample, we found the acoustic measures: Jitter, PPQ and VFO as associated factors for UVFP patient improvement. Those with partial improvement displayed, on average, higher values than these acoustic parameters. Moreover, Jitter measurement was considered a risk factor for the lack of total improvement.

Studies indicate that there is a fundamental frequency influence on Jitter results. Higher fundamental frequency values result in greater Jitter.42,43 The fundamental frequency, Jitter and Shimmer influences are not yet fully understood, and there is a need to conduct new studies to determine the reasons for these relationships.44,45

Considering the aforementioned aspects, we believe that the rate of patients with falsetto voice may have influenced the findings in this study, as this behavior can be found in patients with impaired vocal fold mobility. Brockmann et al.46 found that vocal intensity has a strong impact on Jitter and Shimmer measures. The fundamental frequency had relatively little influence.

Ortega et al.40 conducted a study on patients undergoing thyroid surgeries to determine whether subjective and acoustics voice evaluations could complement or replace laryngoscopy. Seventy-four patients were evaluated before and after surgery and submitted to acoustic analysis, subjective evaluation with GRBASI scale and nasofibrolaryngoscopy. The results indicated that Jitter, noise and harmonic variation proportion displayed the most frequent variations between the first and second evaluations (36% and 31%, respectively). Seven days after surgery, 5 (8%) patients were diagnosed with vocal fold paralysis, with a recovery of 2 cases after one month (5%). GRBASI values, Jitter and Shimmer displayed differences between patients with and without vocal fold paralysis (p<0.05) and (p<0.02). When there was a change in three voice parameters, the vocal fold paralysis was confirmed by laryngoscopy. The authors concluded that vocal fold paralysis might be observed in patients undergoing thyroidectomy, when there is a change in the GRBASI scale, Jitter or major changes of three acoustic analysis parameters. Furthermore, laryngoscopy should be performed only when these parameters have changed.

Observation of these parameters (fundamental frequency, Jitter and Shimmer) is well established as a noninvasive and objective method to quantitatively evaluate dysphonia degree and some different aspects of vocal fold paralysis. These parameters are used to describe normal and pathological voices while providing an objective method that can evaluate treatment clinical efficacy.47,48

Changes in Jitter for UVFP patients should be evaluated more carefully because patients with major changes in this measure may have a worse voice rehabilitation prognosis.

The results obtained in this study indicate that voice rehabilitation improves auditory perceptual, acoustic voice parameters and VHI parameters, in addition to favoring glottal closure in patients with vocal fold paralysis. The results were also stable over a one-year period. The Jitter value, when elevated, is a risk factor for voice therapy success.

The authors declare no conflicts of interest.