Introduction
Functional impairments of the singing voice and small organic pathologic changes of the vocal folds are common problems of singers presenting in phoniatric and laryngological departments [
1,
2]. Non-organic voice disorders that result due to each individual’s particular way of using their voice are classified with various nomenclatures, e.g., ‘Functional Dysphonia’, ‘Muscle Tension Dysphonia’, ‘Vocal Hyperfunction’, ‘Muscle Misuse Dysphonia’ and ‘Muscle Imbalance Dysphonia’ [
3‐
5]. The term ‘Dysodia’ describes the functional problems of the trained singing voice and resembles functional symptoms that occur in the course of singing [
6‐
8]. All of these functional disorders result mainly from inappropriate use of the muscles within the larynx during phonation [
9,
10]. It can appear with overuse of the vocal and vestibular folds (hyperfunctional muscle effort and laryngeal constriction), with underuse (hypofunctional muscle effort causing weakness and insufficient glottal closure), and also with a combination of both hyper- and hypofunctionality, showing smooth transitions of clinical signs and symptoms.
In case of persisting organic findings, the most relevant and common benign vocal fold pathologies comprise marginal swellings, nodules and polyps [
11‐
13]. Localized vocal fold swellings and nodules belong to the group of exudative lesions of Reinke’s space [
14,
15]. Marginal swellings are uni- or bilateral, while nodules are typically bilateral and symmetrical lesions [
16]. They are usually broad-based and appear in the middle third of the membranous part of the vocal folds, the region in which the amplitude has its maximum during phonation [
17,
18]. The findings contain different entities, ranging from soft swellings without fibrous duplication of the underlying stroma to hard keratinized nodules [
19]. Polyps appear in most cases unilaterally at the free margin of the vocal folds [
20]. They are extensions of the lamina propria, which can be clearly differentiated from the surrounding epithelium [
21]. Polyps are usually located between the anterior and the middle third of the vocal fold, at the point of greatest mechanical stress during phonation [
22]. Overstress results in a change of the microstructure of vocal fold mucosa [
23]. Induced vessel trauma leads to hemorrhage, fibrin exudation, thrombosis and proliferation of capillaries [
24]. Teleangiectatic, red-colored polyps are filled with a convolute of cavernous blood compartments with clots and can enlarge to pedunculated mobile findings [
25]. Hyaline translucent polyps consist of lamina propria swellings, which are mostly broad-based and therefore sessile [
26].
Acute phonotrauma as well as chronic excessive or inappropriate use of the voice has the greatest influence on the development of these organic vocal fold lesions [
27‐
29]. Associated symptoms are hoarseness, breathiness, throat discomfort, and unstable voice when speaking or singing [
30‐
32]. Even small pathologic changes are relevant if they cause persistent strain and higher pressure during singing. Singers often lose their high notes and are not able to sing softly in the high register [
33]. Additionally, reduced voice volume, vocal fatigue, and breaks of pitch can occur. If these symptoms are not relieved by carefully applied technical exercises and gentle vocalizing, singers are well advised to consult a medical specialist in the field of phoniatrics or otorhinolaryngology.
The primary therapy is a conservative approach, with voice rest [
34,
35], voice therapy [
36,
37], and treatment of concomitant diseases such as gastroesophageal reflux and allergy [
38,
39]. Surgery is indicated in persisting organic lesions with impaired artistic capabilities, if non-surgical methods prove to be ineffective [
40‐
42]. However, there are few data regarding the specific extent to which different modalities of conservative and surgical interventions improve vocal function [
19].
Conservative treatment recommendations usually comprise the following therapy components compiled by Goffi-Fynn and Carroll [
43]: (1) logopedic training goals including reducing extrinsic laryngeal tension, using a relaxed laryngeal posture, and effective abdominal–diaphragmatic support for all phonation events; particular attention has to be given to the balance of respiratory forces, laryngeal coordination, and optimal filtering of the source signal via resonance and articulatory awareness; and (2) singing training goals, including a lowered breathing pattern to decrease subglottic air pressure, a lower laryngeal position to enable a relaxed laryngeal position, a top–down singing approach to allow for a balanced registration and effective resonance, and the acquisition of sensory and auditory mode of singing monitoring and control.
We offer interdisciplinary voice team consultation hours for singers with functional and organic dysphonia to comprehensively understand and manage the individual singing problem, to safely diagnose and evaluate clinical signs and symptoms, and to initiate a differentiated therapy that corresponds to the singer’s needs. However, there is a need for more research to confirm the superiority of this treatment approach, with implications for vocal health, occupational safety, and health policy.
The purpose of this study was to evaluate the specific outcome of vocal pedagogy (singing lessons), logopedic voice therapy or phonomicrosurgery in singers who suffer from various functional and organic voice problems. Particular attention has been given to the recently introduced parameter vocal extent measure (VEM), which objectively quantifies vocal performance [
44,
45]. The intention has been to investigate VEM changes after therapy and to compare its performance to that of established vocal parameters including the dysphonia severity index (DSI).
Discussion
According to common experience, it appears desirable when the treatment of singers is approached in a multidisciplinary setting with close cooperation between a phoniatrician or laryngologist, a speech language pathologist specialized in voice disorders among singers, and a vocal pedagogue/singing teacher trained in vocology. However, this study aimed at evaluating the specific efficacy of phonosurgery, logopedic treatment and vocal pedagogy in common organic and functional voice problems of singers, including investigation of the recently introduced parameter, VEM. Our results revealed that all three treatment modalities are effective, objectively and subjectively satisfactory therapies to improve the impaired singing voice. Phonosurgery had the largest numeric impact on improvement of vocal function. But even if logopedic voice therapy and vocal pedagogy lead to smaller numeric changes, the voice quality was restored and artistic capabilities recovered. This corresponds to other studies and systematic reviews which proved the effectiveness of phonosurgery in organic dysphonia and comprehensive conservative treatments in functional dysphonia.
Hazlett et al. [
57] reviewed the literature to investigate the impact of voice training on the vocal quality of professional voice users. Most included studies revealed that voice training significantly improved at least one voice-related measure. Many patients in these trials reported that voice training improved the knowledge, awareness and quality of their voice. Ruotsalainen et al. [
58] conducted a systematic review concerning the treatment of functional dysphonia and prevention of voice disorders in adults. As a result, the combination of direct and indirect voice therapy, compared with no intervention, improved self-reported, observer-rated and instrumentally assessed vocal functioning. However, there was no evidence of effectiveness of voice training in preventing voice disorders. Effective treatment options for functional dysphonia in singers comprise indirect therapy (i.e., vocal hygiene, patient education), direct therapy (e.g., voice therapy, circumlaryngeal manual therapy), medical treatment in case of associated laryngopharyngeal reflux or upper airway infections, and phonosurgery for secondary organic lesions [
3,
59]. Comparable to our results, significantly improved objective, subjective and perceptual findings verify positive combined voice therapy effects in patients with functional dysphonia [
60]. Further benefits may result when applying physical therapy or yoga as adjunct treatments [
61,
62]. Yoga practices are not considered a substitute for comprehensive and integrated somatic retraining systems (e.g., Alexander Technique, Feldenkrais); however, by emphasizing kinaesthetic and proprioceptive awareness, singers can facilitate the learning of vocal remediation techniques. Moreover, the influence of singing training on measures of voice quality is also well documented [
63,
64]. Dastolfo-Hromack et al. [
65] investigated singing voice outcomes following singing voice therapy in patients with functional and organic dysphonia. Post-therapeutically, sVHI scores decreased without significant differences between both groups. It is stated that voice care providers should partner with a singing voice therapist to provide optimal care for the singing voice.
In organic dysphonia, our study showed that conservative therapy might also be helpful in singers with small marginal edema, but seems not to be effective for restitution of other chronic findings such as keratinized vocal fold nodules or persistent contact granuloma. Our phonosurgical treatment indication and results are in line with published research data concluding that phonomicrosurgical resection is an adequate therapy to improve the voice in singers suffering from chronic benign glottal lesions [
19,
42]. Comparable to the subgroup of operated patients in our investigation, Zeitels et al. [
40] prospectively studied the outcome in 185 singers and performing artists who underwent phonomicrosurgical excision of different vocal fold lesions. Vocal function was evaluated by means of patient perception, VLS, and objective acoustic and aerodynamic measurements. Postsurgically, objective measurements fell within normal limits, and almost all patients also reported subjective improvement in their vocal function. All singers returned to full vocal activities. do Amaral Catani et al. [
66] performed subjective and objective voice analyses before and 3 months after phonosurgery in 240 professional voice users with various benign vocal fold pathologies. All investigated parameters significantly improved after operation. Obviously, with a correct preoperative diagnosis, a competent and precise phonomicrosurgical procedure (e.g., protection of vocal fold margins, preservation of the lamina propria), a normal postoperative course with regular wound healing, and obeying voice counseling (e.g., 3 days of voice rest, careful vocal rehabilitation), the surgical excision of organic glottal pathologies is a safe, subjectively and objectively satisfactory therapy for the restoration of vocal function.
As a novelty, we examined in our study to which exact extent surgical resection influenced vocal parameters, in order to be able to advise singers about their expected benefit from phonomicrosurgery. The quantitative changes and thus the degree of improvement are indicated by the mean differences between pre- and post-therapeutic voice parameters and the 95% confidence intervals. The range of the increase of MPT (2.0–5.9 s), VEM (8–17) and DSI (0.9–2.0), as well as the decrease of VHI (− 9 to − 6) and sVHI (− 56 to − 40) could serve as reference range for subjective and objective expectation values. If further studies can reveal that the extension of this database with values of future singers enables more precise prognosis about vocal outcome, these values could be quantified for specific diagnosis-related subgroups and used for quality control after phonosurgery. In contrast, the Jitter failed to show a difference in our study. One reason might be the altered time of day during pre- and post-therapeutic voice recordings. According to the process of our clinical routine, most pre-therapeutic measurements were conducted around noon, when patients had time to use and stabilize their voice beforehand. Post-therapeutic check-ups after 3 months took place in the morning without a comparable vocal warm-up. In addition, we know from repeated measurements that the Jitter in general seems to be a rather sensitive parameter, resulting in different consecutive intra-individual values. According to our results, the Jitter as a measurement of irregularities in the frequency seems to be less appropriate to evaluate the success of surgical and conservative voice therapies compared to the other aforementioned parameters.
The recently introduced parameter, VEM, demonstrated significant changes with phonosurgery, logopedic treatment and vocal pedagogy in all singers. This confirmed the results of previous studies where the VEM proved to be a comprehensible and easy-to-use measure for objective evaluation of the VRP [
19,
45]. The standardized VRP and the data thereby determined in order to calculate the DSI are core elements in objective voice diagnostics [
67]. However, the DSI quantifies dysphonia as a negative criterion and involves the risk of inaccurate results due to its multidimensional acquisition [
49]. Additionally, previous studies revealed that the DSI is influenced by differences of measurements of the registration programs as well as by age or gender [
68,
69]. Unimpaired by these interacting factors, we developed the unidimensional VEM for objective VRP evaluation and quantification of vocal performance. The VEM quantifies the subject’s dynamic performance and frequency range, and is calculated as a relationship of the area and the perimeter of the VRP [
44]. The VEM describes the vocal abilities and enables a classification of the voice performance as a positive criterion. Based on our results, this positive measure of vocal function seems to be a compelling diagnostic addition to other established voice measurements and suitable to objectively quantify the vocal performance in singers.
Some study limitations have to be discussed critically when drawing general conclusions. For example, our post-intervention period of 3 months was too short to allow statements about the long-term outcome. Although we did not register any deterioration or relevant recurrences within our follow up, further regular inspections are necessary to ascertain the success of conservative treatments and operations after several years, especially in singers with laryngeal papillomatosis. We advised our patients that the recurrence of vocal fold pathologies cannot be prevented by surgical removal, but that recurrence instead depends on the vocal load after healing, on the speaking and singing technique, and on individual disposition. In addition, the sample size of our study was too small to ensure an informative breakdown for all genres (e.g., musical theater, rap, jazz). Our results indicate a significant improvement for all singing styles; however, a larger pool of singers is required in order to conduct a comparative genre study. Furthermore, the investigated treatment modalities are often used in a combined mode to accelerate recovery and optimize vocal outcome in dysphonic singers. Although we told our patients to stick exclusively to their specific treatment group, we could not control whether they were receiving other, hidden, therapies. Additional singing lessons or logopedic treatment are easily accessible and could influence the results, especially in the recovery of operated patients. Additionally, some general and well-known factors influencing the VRP registration have to be taken into account, such as dependence on the experience of the examiner, the motivation of the singer and the absence of generally accepted specifications concerning the quantity of registered tones. Moreover, the size of the recorded tone intervals affects the VRP circumference. For instance, larger intervals can hide register changes with decreased vocal capability and thus wrongly enlarge the VRP. Most of these errors can be neglected in our study, since all VRPs were recorded by one experienced examiner under practically equal conditions.
Acknowledgements
The authors cordially thank Tony Rymer for manuscript proofreading and our medical technical assistant Julius Rummich for organization of patient investigation and VRP registration. We also sincerely thank all participants of the study.