Effects of speech therapy with or without transcutaneous electrical stimulation on patients with vocal cord paralysis after thoracic surgery
Highlight box
Key findings
• Speech therapy alone and combined with selective electrical stimulation (SES) improved vocal function parameters, with SES showing better glottic closure on the paralyzed side.
What is known and what is new?
• Unilateral vocal fold paralysis (UVFP) is a thoracic surgical complication, and speech therapy aids in rehabilitation.
• SES combined with speech therapy enhances glottic closure efficiency, a novel approach for this patient group.
What is the implication, and what should change now?
• Speech therapy is effective and SES may augment outcomes. Long-term studies are needed.
• Consider SES as an adjunct to speech therapy for persistent UVFP; prioritize multicenter trials to standardize protocols and enhance treatment effectiveness.
Introduction
Background
The recurrent laryngeal nerves (RLNs) exhibit distinct anatomical vulnerabilities; the right branch ascends posterior to the right subclavian artery, whereas the left branch traverses inferior to the aortic arch within the thoracic cavity. This anatomical difference renders the left RLN more susceptible to iatrogenic injury due to its extended intrathoracic course. Thoracic surgical interventions, particularly those involving lymph node dissection along the RLN, are well-established risk factors for unilateral vocal fold paralysis (UVFP), with mechanical trauma, thermal injury, and traction forces constituting the primary etiological mechanisms (1-3). Frequent sequelae include dysphonia and aspiration-related coughing episodes (4,5).
Rationale and knowledge gap
Denervated muscle fibers undergo atrophy prior to reinnervation, and delayed nerve repair can affect the extent of recovery of denervated muscle fibers. Healthy muscle fibers are activated by natural electrical potentials transmitted to the muscles through their innervating nerves, and electrical stimulation can induce equivalent activation of innervated muscle fibers (6). Previous clinical study has found that SES facilitates early functional recovery after unilateral acute facial nerve palsy or vocal cord paralysis (7). However, data on evaluating the actual efficacy of selective electrical stimulation (SES) in UVFP caused by thoracic surgery are still lacking.
Objective
To elucidate the clinical uncertainty in postoperative voice rehabilitation strategies, we analyzed 35 consecutive patients who underwent major thoracic procedures (lobectomy, radical esophageal resection, or mediastinal tumor resection) between March 2021 and September 2024. The patients were stratified into two cohorts based on SES administration to evaluate the comparative therapeutic outcomes. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-864/rc).
Methods
Patients
This retrospective clinical study was conducted through an interdisciplinary collaboration between the Department of Thoracic Surgery and the Otolaryngology Head and Neck Surgery at the Tangdu Hospital. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the institutional review board of Tangdu Hospital of The Fourth Military Medical University (No. XKT-Y-20221120) and informed consent was obtained from all individual participants. The inclusion criteria were as follows: (I) postoperative hoarseness persisting for >3 months despite standard voice rehabilitation and (II) absence of preoperative vocal cord dysfunction. The exclusion criteria were as follows: (I) interval of <3 months between surgery and symptom onset; (II) prior laryngeal surgery or voice therapy; and (III) documented poor treatment adherence. Finally, patients were divided into two groups: those receiving speech therapy (Group A) and those receiving speech therapy and SES (Group B).
Voice quality evaluation methods and tools
A comprehensive voice assessment protocol was implemented to establish personalized rehabilitation plans and evaluate therapeutic outcomes through pre- and postinterventional comparisons at 3-month intervals. The multidimensional evaluation framework incorporated standardized metrics, including the Voice Handicap Index (VHI), which quantifies vocal disability across functional, physical, and emotional domains using severity stratification (≤30: mild, 31–60: moderate, and ≥61: severe). Three certified voice therapists conducted consensus-based evaluations to assess the Grade, Roughness, Breathiness, Asthenia, and Strain (GRBAS) parameters on a 0–3 severity scale. Objective acoustic measurements were obtained using the ATMOS LingWAVES system [Sound Pressure Level (SPL) microphone; 30–130 dB frequency response; 44.1 kHz sampling rate; (ATMOS, Lenzkirch, Germany)], with patients sustaining phonetically balanced vowels (/aː/, /oː/, /eː/) at conversational intensity for triplicate recordings. The fundamental frequency, jitter, shimmer, and harmonic-to-noise ratio of the samples were derived. Pre- and postintervention video laryngostroboscopy (Olympus CV-170/ENF-V3) was used to quantify glottic closure during sustained /iː/ phonation objectively, and was analyzed by blinded laryngologists. The Dysphonia Severity Index (DSI) provides quantitative voice quality assessment through its multidimensional formula: 0.13 × maximum phonation time (MPT) (s) + 0.0053 × F0max (Hz) − 0.26 × SPLmin (dB) − 1.18 × jitter (%) + 12.4, where prolonged MPT reflects enhanced respiratory-phonatory coordination (8,9).
Voice treatment methods
Individualized voice therapy protocols were developed based on comprehensive diagnostic assessments, incorporating modified principles from an evidence-based ABCLOVE (activate exercises, breathing, counseling, laryngeal manipulation, oral resonance, vocal exercises, and elimination of habits) rehabilitation framework (10). Patients participated in structured biweekly 45-min sessions over 12 weeks, with training cohorts organized into either individual (1:1) or small-group (2–3 participants) formats. Adherence protocols required daily home practice in accordance with therapist-prescribed regimens, with vocal exercises temporarily suspended during intercurrent respiratory infections until complete resolution of symptoms.
The therapeutic regimen consisted of five sequential laryngeal re-education techniques (11). The first was the throat-swing movement, in which the patient relaxed the shoulder and neck while using the thumb and fingers to stabilize the thyroid cartilage. The cartilage was swung to the left and right with a small amplitude and high frequency, whilst producing the “ah-ah” sound at the same time to promote laryngeal muscle relaxation. Both the swinging motion and phonation were stopped simultaneously, followed by nasal inhalation. Ten repetitions per set, with short and powerful pronunciations. Second, humming, in which the patient breathed naturally, and the nasal tone was ‘humming’, through inhaling with the nose. Ten repetitions per set and the pronunciation points were the same as those described previously (Video 1). Third, bubble blowing, in which the patient put one end of a pipette into the water cup. While inhaling through the nose and holding the pipette in the mouth, they continuously exhaled into the water to generate bubbles and relax their vocal cords, repeating this ten times per set. Fourth, soft voice movement, in which patients with a baseline slow rhythm pronunciation /ma---/ use natural breathing, and then alternate between faster rhythm pronunciation /ma--/and the baseline (Video 2). Fifth, in the slippery sound movement, the patient inhaled deeply through the nose and emitted the sound /wu/ from the lowest pitch (bass) to the highest pitch. This was followed by a breath-hold of approximately 3 seconds, followed by slow exhalation through the mouth to promote vocal fold relaxation.
Stimulation
Surface stimulation was performed using VitalStim® 5900 Swallowing Disorder Therapeutic Instrument (CA, USA). Bilateral electrode patches (5×5 cm conductive silicone rubber) were positioned at two anatomical landmarks: (I) the thyroid cartilage plate corresponding to the laryngeal prominence, and (II) the carotid sheath region along the vagus nerve pathway on the affected side in patients with unilateral vocal cord paralysis. Electrical stimulation was administered using a biphasic pulsed current waveform with parameters set at 6 mA intensity and 100-second pulse width (12-17). Treatment sessions were conducted three times a week, each lasting 20 minutes, with skin impedance maintained below 5 kΩ through the use of standardized electrode gel. The stimulation intensity was titrated to achieve visible thyrohyoid muscle contraction without inducing laryngeal discomfort (visual analog scale <2/10) (Figure 1).
Statistical analyses
All continuous data were presented as median (IQR) or mean ± standard deviation (SD) based on the distribution. Differences between the two groups were analyzed using the Wilcoxon signed-rank test and the Chi-squared test, with Fisher’s two-sided test applied for the latter. Statistical significance was set at P<0.05. Standard statistical analyses were performed using IBM SPSS Statistics version 25.0.
Results
In total, 35 patients were included in this study, with an average age of 55.6±10.7 years (range, 26–80 years) (Table 1), including one patient with benign pulmonary nodules who underwent lobectomy + lymph node sampling, 20 patients who underwent lobectomy + lymph node dissection, eight patients with malignant esophageal tumors who underwent total endoscopic radical resection of esophageal cancer (partial resection of the esophagus and stomach, esophagogastric neck anastomosis + lymph node dissection), and six patients who underwent mediastinal tumor resection (Tables 2,3).
Table 1
| Characteristics | Overall (N=35) | Group A (n=19) | Group B (n=16) | P value |
|---|---|---|---|---|
| Age (years) | 58 (51, 62) | 59 (51, 62) | 56 (51, 61) | 0.41 |
| Gender | 0.97 | |||
| Female | 13 [37] | 7 [37] | 6 [38] | |
| Male | 22 [63] | 12 [63] | 10 [63] | |
| Body mass index (kg/m2) | 23.03 (22.04, 24.22) | 23.44 (22.69, 24.22) | 22.54 (20.41, 23.87) | 0.24 |
| Smoking history | 15 [43] | 6 [32] | 9 [56] | 0.14 |
| Drinking history | 7 [20] | 3 [16] | 4 [25] | 0.68 |
| ASA score | 0.10 | |||
| 1 | 1 [3] | 0 | 1 [6] | |
| 2 | 2 [5.7] | 0 | 2 [12] | |
| 3 | 18 [51] | 9 [47] | 9 [56] | |
| 4 | 14 [40] | 10 [53] | 4 [25] | |
| Hypertension | 9 [26] | 5 [26] | 4 [25] | >0.99 |
| Diabetes | 1 [3] | 0 | 1 [6] | 0.46 |
| Heart failure | 1 [3] | 1 [5] | 0 [0] | >0.99 |
Data are presented as median (25th, 75th percentile) for continuous data and n [%] for categorical data. Group A: speech therapy; Group B: speech therapy and SES. ASA, American Society of Anesthesiologists; SES, selective electrical stimulation.
Table 2
| Surgery type | Frequency | Side | ||
|---|---|---|---|---|
| Right | Left | Both | ||
| Lobectomy + lymph node dissection/sampling | 21 | 3 | 17 | 1 |
| Esophageal cancer radical surgery | 8 | NA | NA | NA |
| Mediastinal tumor resection | 6 | NA | NA | NA |
NA, not available.
Table 3
| Disease type | Total | Group A | Group B | P value |
|---|---|---|---|---|
| Benign lung disease | 1 | 0 | 1 | 0.61 |
| Primary lung malignancy | 20 | 11 | 9 | |
| Malignancy of the esophagus | 8 | 5 | 3 | |
| Mediastinal tumor | 6 | 3 | 3 |
Group A: speech therapy; Group B: speech therapy and SES. SES, selective electrical stimulation.
The patients received voice rehabilitation treatment and were divided into Groups A and B according to their SES. The clinical results after 3 months were statistically analyzed. No treatment-related complications were observed.
As shown in Table 4, the VHI and GRBAS scores in both groups were significantly lower than before training (P<0.05). Electronic laryngoscopy revealed that in Group B, two patients transitioned from completely unclosed to moderately incomplete closure, and two patients achieved complete closure (Video 3). The electronic laryngoscope revealed that among Group B patients, two patients transitioned from complete nonclosure to moderate incomplete closure, while two patients shifted from complete nonclosure to complete closure (P<0.05). As shown in Table 5, SES may facilitate the closure of the affected glottis.
Table 4
| Voice parameters | No. of patients | Pretintervention | Postintervention | Z | P value |
|---|---|---|---|---|---|
| Glottal closure degree | |||||
| Group A | 19 | 3.00 (3.00, 3.00) | 3.00 (3.00, 3.00) | 0 | >0.99 |
| Group B | 16 | 3.00 (3.00, 3.00) | 3.00 (2.25, 3.00) | −1.857 | 0.06 |
| VHI | |||||
| Group A | 19 | 54.00 (41.00, 74.00) | 17.00 (12.00, 25.00) | −3.823 | <0.001 |
| Group B | 16 | 61.00 (45.75, 80.75) | 21.00 (18.25, 27.75) | −3.517 | <0.001 |
| GRBAS | |||||
| Group A | 19 | 14.00 (11.00, 14.00) | 3.00 (5.00, 7.00) | −3.849 | <0.001 |
| Group B | 16 | 15.00 (12.25, 15.00) | 6.00 (3.25, 7.75) | −3.531 | <0.001 |
Data are presented as median (25th, 75th percentile). Glottal closure, 0 points; completely closed, 1 point; slightly incomplete closure, 2 points; moderately incomplete closure, 3 points; serious incomplete closure. Group A: speech therapy; Group B: speech therapy and SES. GRBAS, Grade, Roughness, Breathiness, Asthenia, and Strain; SES, selective electrical stimulation; VHI, Voice Handicap Index.
Table 5
| Voice parameters | Group A | Group B | P value |
|---|---|---|---|
| Glottic closure | 0.04 | ||
| Not improved | 19 [100] | 12 [75] | |
| Improved | 0 | 4 [25] | |
| VHI ≥61 (severe) | >0.99 | ||
| Not improved | 0 | 0 | |
| Improved | 8 [100] | 8 [100] | |
| GRABS | >0.99 | ||
| ≥12 | 0 | 0 | |
| <12 | 13 [100] | 13 [100] |
Data are presented as n [%]. Group A: speech therapy; Group B: speech therapy and SES. GRBAS, Grade, Roughness, Breathiness, Asthenia, and Strain; SES, selective electrical stimulation; VHI, Voice Handicap Index.
As shown in Table 6, the jitter, shimmer, harmonic noise ratio (HNR), MPT, and DSI of Groups A and B significantly decreased after vocal rehabilitation (P<0.05). Although the F0 of Group B improved after treatment, there was no significant change in the F0 of the two groups after training (P>0.05).
Table 6
| Voice parameters | No. of patients | Pretintervention | Postintervention | Z | P value |
|---|---|---|---|---|---|
| F0 | |||||
| Group A | 19 | 166.51 (105.74, 239.72) | 164.19 (140.87, 208.95) | 0 | >0.99 |
| Group B | 16 | 101.80 (65.82, 224.47) | 160.16 (108.53, 197.75) | −1.500 | 0.13 |
| Jitter local (%) | |||||
| Group A | 19 | 2.48 (0.28, 13.95) | 0.23 (0.15, 0.36) | −3.002 | 0.002 |
| Group B | 16 | 9.23 (0.87, 15.90) | 0.59 (0.21, 1.77) | −3.124 | 0.002 |
| Shimmer local (%) | |||||
| Group A | 19 | 10.21 (3.72, 21.03) | 0.23 (0.15, 0.36) | −3.099 | 0.002 |
| Group B | 16 | 17.50 (9.95, 21.53) | 4.67 (2.77, 7.59) | −3.464 | 0.001 |
| HNR (dB) | |||||
| Group A | 19 | 0.26 (0.19, 0.37) | 0.54 (0.46, 0.66) | −3.825 | <0.001 |
| Group B | 16 | 0.21 (0.16, 0.30) | 0.43 (0.35, 0.46) | −3.352 | 0.001 |
| MPT (s) | |||||
| Group A | 19 | 4.54 (3.18, 6.84) | 8.80 (7.25, 10.47) | −3.300 | 0.001 |
| Group B | 16 | 4.00 (2.43, 5.67) | 8.30 (7.30, 10.08) | −3.516 | <0.001 |
| DSI | |||||
| Group A | 19 | −6.40 (−1.00, −10.00) | 2.90 (1.60, 3.90) | −3.823 | <0.001 |
| Group B | 16 | −7.70 (−2.90, −10.00) | 4.35 (2.73, 8.28) | −3.516 | <0.001 |
Data are presented as median (25th, 75th percentile). Group A: speech therapy; Group B: speech therapy and SES. DSI, Dysphonia Severity Index; F0, frequency; HNR, harmonic-to-noise ratio; MPT, longest pronunciation time; SES, selective electrical stimulation.
Discussion
Key findings
In thyroid surgery, RLN injury is often caused by iatrogenic factors and nerve continuity is often preserved, laying the foundation for axonal regeneration and functional recovery. In addition, the thyroid surgery site is superficial, and early postoperative rehabilitation interventions can be initiated. However, the prognosis of RLN injury caused by thoracic surgery is poor, and video-assisted thoracic lobectomy remains the standard treatment for early-stage lung cancers. However, during surgery, it is easy to cut off the nerves because of tumor infiltration, radiation damage, or complete removal of the lesion. This type of injury is often permanent and irreversible, and may be accompanied by tracheoesophageal dysfunction, further exacerbating speech function impairment (18,19), particularly at station 4 L, which results in postoperative vocal fold paralysis. Our findings align with established evidence demonstrating the predominance of left-sided RLN paralysis (2,18). Esophageal cancer primarily metastasizes to the RLN pathway and the associated lymph node basins. The standard surgical approach, involving left-sided cervical esophageal mobilization during gastric conduit reconstruction, is inherently vulnerable to RLN trauma. Intraoperative injury is primarily caused by electrosurgical dissection, mechanical traction, or compressive forces. Postoperative inflammatory processes (e.g., such as edema and hematoma) are additional contributors (19). In thoracic surgery at our center, except in cases of tumor invasion of the RLN, the RLN is strictly avoided during surgery.
Speech therapy is a targeted therapeutic approach for dysphonia management that employs systematic exercises to enhance neuromuscular coordination of the laryngeal structures. The intervention protocol aimed to optimize vocal fold viscoelasticity by strengthening the adductor and abductor muscles, while improving glottic closure efficiency. Concurrently, suprahyoid and infrahyoid muscle conditioning were implemented to augment phonatory power and articulatory precision.
SES is an established treatment modality for plastic surgery and physical rehabilitation, although its application in human laryngeal neuroregeneration remains under investigation (20). Studies have demonstrated that SES promotes neural repair through two synergistic mechanisms: neuroelectric signal modulation to activate axonal regeneration, and vasodilation-mediated neurotrophic support, which reduces perineural edema and inflammation. Therapeutic intervention also prevents muscular atrophy by preserving baseline contractile strength, myofibrillar mass, and resting muscle tone during the denervation-reinnervation transition period (21-23).
The Speech Handicap Index quantifies dysphonia severity, while the VHI provides a validated multidimensional assessment across physical, functional, and emotional domains (24,25). The clinician-rated GRBAS Perceptual Scale uses standardized auditory-perceptual parameters. Postintervention analyses showed significant intergroup improvements in both patient self-assessments and clinician evaluations.
Computerized acoustic systems objectively quantify vocal pathologies through multiparametric phonatory signal analysis, with core biomarkers including F0, jitter, shimmer, HNR, and MPT (26). F0 correlates with laryngeal morphology, pitch, and vocal-fold biomechanics (27). HNR quantifies periodic vs. aperiodic glottal energy; lower ratios indicate increased spectral noise in dysphonia (28).
MPT assesses voice therapy effectiveness by evaluating vocal airflow/volume, with increased MPT potentially from improved glottic occlusion (27,29). Frequency (F0): the fundamental frequency refers to the natural frequency of vocal-fold vibrations. It is closely related to the mass and volume of the vocal folds as well as the regulation of the cricothyroid muscle, thyroarytenoid muscle, and sound pressure. Vocal fold injuries can be reflected in F0. The fundamental frequency is typically measured in hertz (Hz), which represents the number of vibrations of the vocal folds per second. Based on the characteristics of the Chinese voice, we defined F0 as <110 Hz in males and less than 220 Hz in females as the low fundamental frequency of the voice (30). Pretreatment evaluation identified 11 Group A and 7 Group B patients with subthreshold F0 values. Post-therapeutic analysis revealed residual hypophonia in four Group A and two Group B cases, potentially attributable to SES-mediated neuroregeneration kinetics exceeding our 6-month observation window. Nevertheless, both groups demonstrated statistically significant improvements in quantitative voice parameters, including perturbation indices and DSI, with comparable MPT prolongation (P<0.05), indicating a reduction in glottic insufficiency across treatment modalities. Using electronic laryngoscopy, we found that SES better closed the affected side of the glottis and achieved better glottic closure. Although Group B showed inferior baseline parameters, a comparison of the treatment effects between the two groups revealed that Group B still achieved an excellent treatment effect comparable to that of Group A.
limitations
This study has some limitations. First, the single-center retrospective design, with its limited statistical power, restricts the generalizability of our findings. Second, longitudinal outcomes, including phonatory function trajectories and quality-of-life metrics, remain undetermined, necessitating extensive observational studies. Third, Group B showed worse baseline parameters (e.g., jitter and shimmer); there was a certain difference between the two sets of baseline data, and the inclusion criterion requiring ≥3 months post-onset vocal fold paralysis introduced potential confounding from natural recovery processes. Notably, the study cohort demonstrated a selection bias inherent in prioritizing acute oncological care over phoniatric rehabilitation among esophagectomy patients with RLN injury who frequently presented with competing comorbidities requiring urgent clinical intervention.
Conclusions
Phoniatric rehabilitation demonstrated significant therapeutic efficacy in normalizing vocal biomarkers in patients with UVFP following thoracic surgical interventions, whereas adjunctive SES application promoted neuromodulation-enhanced vocal fold mobility restoration on the paralyzed side. This dual-modality intervention synergistically improved glottic competence through enhanced vibratory margin closure, and achieved measurable voice quality optimization. Subsequent investigations should prioritize comparative analysis of neuromuscular stimulation paradigms, establishment of evidence-based treatment protocols, and longitudinal evaluation of sustained therapeutic outcomes.
Acknowledgments
None.
Footnote
Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-864/rc
Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-864/dss
Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-864/prf
Funding: This work was supported by
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-864/coif). The authors have no conflicts of interest to declare.
Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the institutional review board of Tangdu Hospital of The Fourth Military Medical University (No. XKT-Y-20221120) and informed consent was obtained from all individual participants.
Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.
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