Human voice production involves the synchronization of optimal glottic positioning with the control of the airflow from the lungs to the oropharynx. The vocal folds must be of proper compliance to exhibit their dynamic vibratory characteristics. Factors that influence either the aerodynamic configuration (ie, vocal fold paralysis) or the vibratory property of the glottis (ie, laryngeal cyst) may result in dysphonia. However, when vocal quality deteriorates in the absence of anatomic and neurologic factors, a functional voice disorder should be suspected.
Functional voice disorders may account for up to 40% of the cases of dysphonia referred to a multidisciplinary voice clinic. [1, 2] Altered laryngeal muscle tension is believed to result in altered laryngeal performance despite normal anatomy.  As a result, the term muscle tension dysphonia (MTD) has become the preferred term for functional dysphonia. An Italian study found that approximately 90% of children with dysphonia from a vocal fold lesion had an underlying functional dysphonia. 
See the videos below for five case studies.
A complete history must be taken, including characterization of the patients' specific vocal symptoms and any precipitating factors. A recent upper respiratory infection may serve as a catalyst that forces an already stressed laryngeal system into a more severely imbalanced state. Vocation (ie, singing, athletic coaching) and misuse of the voice in this vocation must be assessed. Patient questionnaires, such as the Voice Handicap Index (VHI), are frequently administered. A German study found that while patients with dysphonia due to an organic etiology and those with FD both had higher VHI scores than nondysphonic controls, the scores between the 2 dysphonic groups were not significantly different. 
The patient's general health, including medications, should be reviewed. Neurologic disorders such as generalized dystonia or myasthenia gravis should be excluded. Any history of laryngeal trauma or neural injury resulting from prior neck surgery or trauma should be obtained. A history of temporomandibular joint disorders, cervical myalgia, or muscular fatigue may be suggestive of a pattern of hyperfunction. Other medical disorders, including laryngopharyngeal reflux as well as endocrinopathies such as hypothyroidism, must be assessed. 
Any psychiatric history or recent history of psychosocial stressors should be elicited. Patients with functional dysphonia are more likely than controls to have symptoms of depression, nonspecific and general anxiety, and specific anxiety concerning health.  A complete social history must be obtained to evaluate for exposure to irritants such as tobacco smoke, alcohol, caffeine, dairy products, chocolate, mints, and occupational irritants.
Initial assessment of vocal quality for the range ease, volume, and quality of the voice occurs during the patient interview. All patients must undergo a complete ear, nose, and throat examination to assess nasal airway patency, pharyngeal function, and velopharyngeal competency. Hearing loss may result in voice strain due to altered biofeedback. Pulmonary analysis may reveal air wasting (exhalation before phonation) or limited chest excursion. Diminished breath support, particularly with patients using long run-on sentences, may stress the laryngeal system, leading to altered mechanics.
A thorough laryngeal examination is required, ideally with stroboscopy evaluation. Although functional dysphonia is typically defined as dysphonia in the setting of normal anatomy and neurologic function, certain vocal fold lesion such as nodules and granulomas may be the result of vocal trauma from persistent patterns of underlying functional dysphonia. Although a flexible endoscope traditionally has less resolution than a rigid endoscope, the ability to evaluate the larynx with a flexible endoscope during connected speech allows for more complete voice analysis. Distal chip technology has improved the image resolution of flexible endoscopes.
Findings on laryngoscopy that have been associated with functional dysphonia include laryngeal isometry, plica ventricularis (false fold compression), anterior-posterior compression, incomplete adduction/posterior glottal chink, and hard glottal attack. Classification systems to describe laryngeal findings have been proposed by Morrison et al and by Van Lawrence. [8, 9] However, Sama et al reporting that a more than 60% of a nondysphonic population demonstrated at least 1 feature of laryngeal hyperfunction as described by Morrison and Van Lawrence. The authors concluded that the laryngoscopy features associated with functional dysphonia are commonly seen in a control population and do not separate patients with functional dysphonia from nondysphonic patients. 
With the popularization of fiberoptic laryngoscopy, Koufman reported 4 basic patterns of muscle tension dysphonia (MTD) that may be seen in both functional dysphonia and those patients with organic lesions. For those patients with organic lesions, these patterns tend to be compensatory.  These types of muscle tension dysphonia (MTD) are as follows:
Type I: Glottic/laryngeal isometry features a posterior chink due to simultaneous (and inappropriate) contraction of the posterior cricothyroid muscle and lateral cricoarytenoid muscle during phonation.
Type II: Supraglottic/plica ventricularis is A false vocal fold approximation that may be functional or compensatory.
Type III: Supraglottic/partial anterior-posterior contraction.
Type IV: Supraglottic/complete anterior-posterior contraction in which the petiole of the epiglottis approximates the arytenoids.
A classification system of characterizing functional voice disorders was proposed by Koufman in 1982, including the categories of conversion aphonia/dysphonia, habituated hoarseness, inappropriate falsetto, vocal abuse syndrome, postoperative dysphonia, and relapsing aphonia.  Vocal abuse syndrome accounts for over 70% of functional dysphonia in this system. Others advocate the umbrella term of “muscle tension dysphonia.” In these systems, subtypes of muscle tension dysphonia (MTD) can be used including psychogenic, habituated, compensatory, and organic abnormalities resulting from misuse or abuse. 
The development of conversion dysphonia, also referred to as a psychogenic dysphonia, may result from a temporally related psychologically or emotionally traumatic event. Conversion disorder is a somatoform disorder in which the symptoms are not intentionally produced or feigned by the patient. The patient's vocal quality is usually hypofunctional or aphonic. Fiberoptic laryngoscopy may demonstrate a lack of vocal cord adduction during attempted phonation. However, coughing and throat clearing (vegetative phonation) demonstrate normal vocal cord adduction. The treatment is voice therapy. Patients may also require psychotherapy to address the underlying psychological trauma.
Patients experiencing falsetto (also called puberphonia or mutational falsetto) present with a stable dysfunction of pitch control. The typical patient is a young male of pubertal age whose voice fails to descend to a normal adult pitch level at puberty. Falsetto is typically responsive to voice therapy. Occasionally, psychological counseling or botulism toxin injection of the cricothyroid muscle may be beneficial. 
Dysphonia may develop and persist after an acute episode such as viral infection, chemical/irritant exposure, or laryngeal surgery. A “secondary gain” is frequently present. Patients may experience laryngeal fatigue or pain. The voice tends to be consistent with voice quality described as breathy, raspy, or diplophonic. Laryngeal examination reveals normal anatomy but poor vibration and closure. Response to voice therapy is very good.
Excessive tension of the laryngeal or extralaryngeal muscle or both may result in altered phonatory function. This hyperfunctional activity, however, may be in response to an underlying organic condition such as trauma, infection, or diminished subglottic airflow pressures from impaired pulmonary function. Patients with vocal fold bowing (presbylarynx) were 17 times more likely to demonstrate hyperfunctional muscle tension dysphonia (MTD) patterns.  Patients with muscle tension dysphonia (also called tension-fatigue syndrome) may manifest other symptoms of muscle tension such as neck and shoulder strain. Extended periods of voice use result in vocal effort and fatigue that intensifies over time. Laryngeal exam may reveal poor glottal closure. Voice therapy may help “unload” the hyperfunction and tension found in the larynx. The underlying glottic condition may also need to be treated for continued improvement.
Organic lesions from muscle tension dysphonia
Although compensatory muscle tension dysphonia (MTD) behavior occurs as a result of an organic condition, the hyperfunctional behavior of muscle tension dysphonia (MTD) may result in an anatomic lesion such as nodules, edema, or granulomas. Patients present with complaints of discomfort, effort, and fatigue. Nodules, which are the most common presentation of a functional dysphonia in children, present as bilateral lesions at the junction of the anterior and middle third of the vocal fold. Jiang et al found that mechanical intraepithelial stress plays an important role in the development of vocal nodules, polyps, and other lesions that are usually ascribed to hyperfunctional dysphonia.  Granulomas are associated with reflux and are frequently preceded by endotracheal intubation.
Treatment & Management
All voice rehabilitation should include the elimination of vocally abusive behaviors such as throat clearing, habitual yelling or screaming, habitual breath holding, or improper glottic valving during exercise. Inhaled irritants such as tobacco and toxic chemicals should be avoided. Gastroesophageal reflux should be controlled. Patients should demonstrate proper fluid intake, and medications with drying potential should be minimized to optimize laryngeal hydration. 
Stemple has classified the different treatment philosophies of voice therapy into the following 5 categories: 
Symptomatic voice therapy addresses the identification and elimination of vocally abusive behaviors through facilitating approaches. These techniques facilitate a target or a more optimal vocal response by the patient. Examples include auditory feedback, head positioning, laryngeal massage, and relaxation. Disorders of misuse or abuse benefit from this treatment philosophy.
Psychogenic voice therapy addresses the underlying emotional and psychosocial issues that are causing the dysphonia. Patients with conversion dysphonia would benefit from this approach.
Etiological voice therapy focuses on recognition and elimination of the cause of the voice disorder, which may be multifaceted. Muscle tension dysphonia may benefit from this approach.
Physiologic voice therapy, a type of biofeedback, involves the use of acoustic and aerodynamic analysis to direct the patient's vocal function back to objectively normative physiologic voice function. Physiologic voice therapy may be useful on a patient with falsetto.
Others classify voice therapy into 2 categories: direct and indirect. Direct techniques focus on voice production and include techniques such as the yawn-sigh method, optimal pitch establishment, and laryngeal manipulation. [19, 20] Indirect techniques focus on reducing the etiologic factor that cause the voice problem and include auditory training and patient education.  Through a meta analysis, Ruotsalainen et al concluded that comprehensive voice therapy was effective in “improving vocal performance in adults with functional dysphonia,” but no evidence was found that voice training prevented voice disorders. 
In certain cases, neuropsychiatric evaluation may be needed to address the inciting factor. In a prospective study, Daniilidou reported that the addition of cognitive behavioral therapy to traditional voice therapy was more effective in the treatment of functional dysphonia than voice therapy alone. 
A study by Tomlinson and Archer suggested that physical therapy may aid patients with muscle tension dysphonia (MTD). In the study, nine patients with MTD underwent a series of physical therapy sessions, which included manual therapy, exercise, and stress management education. After therapy concluded, all of the patients showed improvement on the Patient-Specific Functional Scale, including seven whose scores exceeded those demonstrating clinically meaningful improvement. In addition, three patients demonstrated clinically meaningful changes in their Voice Handicap Index (VHI) scores. Cervical flexion and lateral flexion and jaw opening improved in all patients, while cervical extension and rotation improved in eight of them. Moreover, eight patients were pain-free following treatment. 
However, a study by Craig et al found that in patients with muscle tension dysphonia, median improvement of the VHI score for those with moderate to severe VHI scores at baseline did not significantly differ between patients treated with voice therapy alone, with a combination of voice therapy and physical therapy, or with physical therapy alone. Nonetheless, the investigators suggested that physical therapy may be effective in a subset of muscle tension dysphonia patients. 
Some cases of muscle tension dysphonia may remain refractory to intense voice therapy. In these cases, the original diagnosis must be reexamined. Dworkin reported a small series of patients that responded to voice therapy after a topical application of 4% lidocaine.  Some have hypothesized that lidocaine may interrupt the sensory feedback that contributes to hyperfunctional behavior. In cases of compensatory muscle tension dysphonia, once the hyperfunctional behavior has been reduced, attention to the underlying etiology may be needed. For example, injection laryngoplasty or medialization thyroplasty may be needed to correct glottal insufficiency.