Dysphonia

Dysphonia, commonly referred to as hoarse voice, refers to dysfunction in the ability to produce voice.^[1][2] For voice to be classified as "dsyphonic", abnormalities must be present in one or more vocal parameters: pitch, loudness, quality, or variability.^[2] Perceptually, dysphonia can be characterized by hoarse, breathy, harsh, or rough vocal qualities, but some kind of phonation remains.^[2]

Current prevalence rates suggest that dysphonia is higher in females and the elderly, however, it can be found in both sexes and across the lifespan.^[3] Furthermore, certain occupational groups, such as teachers and singers, may be at increased risk for developing dysphonia.^[4][5]

Dysphonia can be categorized into two broad main types: organic and functional. The type of dysphonia is dependent on the etiology (i.e. cause) of the pathology. While the causes of dysphonia can be divided into five basic categories, all of them result in an interruption of the ability of the vocal folds to vibrate normally during exhalation, which affects the voice. The assessment and diagnosis of dysphonia is done by a multidisciplinary team, and involves the use of a variety of subjective and objective measures, which look at both the quality of the voice as well as the physical state of the larynx.Multiple treatments have been developed to address organic and functional causes of dysphonia. Dysphonia can be targeted through direct therapy, indirect therapy, medical treatments, and surgery. Functional dysphonias may be treated through direct and indirect voice therapies, whereas surgeries are recommended for chronic, organic dysphonias.^[6]

Definition/classification

Dysphonia is a broad clinical term which refers to abnormal functioning of the voice.^[1][2] More specifically, a voice can be classified as “dysphonic” when there are abnormalities or impairments in one or more of the following parameters of voice: pitch, loudness, quality, and variability.^[2] For example, abnormal pitch can be characterized by a voice that is too high or low whereas abnormal loudness can be characterized by a voice that is too weak or loud.^[2] Similarly, a voice that has frequent, inappropriate breaks characterizes abnormal quality while a voice that is monotone (i.e., very flat) or inappropriately fluctuates characterizes abnormal variability.^[2] While hoarseness is used interchangeably with the term dysphonia, it is important to note that the two are not synonymous. Hoarseness is merely a subjective term to explain the perceptual quality (or sound) of a dysphonic voice.^[7] While hoarseness is a common symptom (or complaint) of dysphonia,^[1] there are several other signs and symptoms that can be present such as: breathiness, roughness, and dryness. Furthermore, a voice can be classified as dysphonic when it poses problems in the functional or occupational needs of the individual or is inappropriate for their age or sex.^[2]

Types

Voice disorders can be divided into 2 broad categories: organic and functional.^[8] The distinction between these broad classes stems from their etiology, whereby organic dysphonia results from some sort of physiological change in one of the subsystems of speech (for voice, usually respiration, laryngeal anatomy, and/or other parts of the vocal tract are affected). Conversely, functional dysphonia refers to hoarseness resulting from vocal use (i.e. overuse/abuse).^[9] Furthermore, according to ASHA, organic dysphonia can be subdivided into structural and neurogenic; neurogenic dysphonia is defined as impacted functioning of the vocal structure due to a neurological problem (in the central nervous system or peripheral nervous system); in contrast, structural dysphonia is defined as impacted functioning of the vocal mechanism that is caused by some sort of physical change (e.g. a lesion on the vocal folds).^[9] Notably, an additional subcategory of functional dysphonia recognized by professionals is psychogenic dysphonia, which can be defined as a type of voice disorder that has no known cause and can be presumed to be a product of some sort of psychological stressors in one’s environment.^[9][10] It is important to note that these types are not mutually exclusive and much overlap occurs. For example, Muscle Tension Dysphonia (MTD) has been found to be a result of many different etiological factors including the following: MTD in the presence of an organic pathology (i.e. organic type), MTD stemming from vocal use (i.e. functional type), and MTD as a result of personality and/or psychological factors (i.e. psychogenic type).^[9][11]

Causes

A variety of different cause, which result in abnormal vibrations of the vocal folds, can cause dysphonia. These causes can range from vocal abuse and misuse to systemic diseases. Causes of dysphonia can be divided into five basic categories, although overlap may occur between categories.^{[12][13][14][15]} (Note that this list is not exhaustive):

Mechanism

Located in the anterior portion of the neck is the larynx (also known as the voice box), a structure made up of several supporting cartilages and ligaments, which houses the vocal folds.^[1] In normal voice production, exhaled air moves out of the lungs and passes upward through the vocal tract.^[1] At the level of the larynx, the exhaled air causes the vocal folds to move toward the midline of the tract (a process called adduction). The adducted vocal folds do not close completely but instead remain partially open. The narrow opening between the folds is referred to as the glottis.^[1][2] As air moves through the glottis, it causes a distortion of the air particles which sets the vocal folds into vibratory motion. It is this vibratory motion that produces phonation or voice.^[2] In dysphonia, there is an impairment in the ability to produce an appropriate level of phonation. More specifically, it results from an impairment in vocal fold vibration or the nerve supply of the larynx.^[2]

Diagnosis

The assessment and diagnosis of a dysphonic voice is completed by a multidisciplinary team, and involves the use of both objective and subjective measures to evaluate the quality of the voice as well as the condition of the vocal fold tissue and vibration patterns.^[16]

Auditory-perceptual measures

Auditory-perceptual measures are the most commonly used tool by clinicians to evaluate the voice quality due to its quick and non-invasive nature.^[17] Additionally, these measure have been proven to be reliable in a clinical setting.^[18] Ratings are used to evaluate the quality of a patient's voice for a variety of voice features, including overall severity, roughness, breathiness, strain, loudness and pitch. These evaluations are done during spontaneous speech, sentence or passage reading or sustained vowel productions.^[15] The GRBAS (Grade, Roughness, Breathiness, Asthenia, Strain) and the CAPE-V (Consensus Auditory Perceptual Evaluation—Voice) are two formal voice rating scales commonly used for this purpose.^[17]

Vocal fold imaging

Vocal fold imaging techniques are used by clinicians to examine the vocal folds and allows them to detect vocal pathology and assess the quality of the vocal fold vibrations. Laryngeal stroboscopy is the primary clinical tool used for this purpose. Laryngeal stroboscopy uses a synchronized flashing light passed through either a rigid or flexible laryngoscope to provide an image of the vocal fold motion; the image is created by averaging over several vibratory cycles and is thus not provided in real-time.^[19] As this technique relies on periodic vocal fold vibration, it cannot be used in patients with moderate to severe dysphonia.^[15] High speed digital imaging of the vocal folds (videokymography), another imaging technique, is not subject to the same limitations as laryngeal stroboscopy. A rigid endoscope is used to take images at a rate of 8000 frames per second, and the image is displayed in real time. As well, this technique allows imaging of aperiodic vibrations^[15] and can thus be used with patients presenting with all severities of dysphonia.

Acoustic Measures

Acoustic measures can be used to provide objective measures of vocal function. Signal processing algorithms are applied to voice recordings made during sustained phonation or during spontaneous speech.^[20] The acoustic parameters which can then be examined include fundamental frequency, signal amplitude, jitter, shimmer, and noise-to-harmonic ratios.^[15] However, due to limitations imposed by the algorithms employed, these measures cannot be used with patients who exhibit severe dysphonia.^[20]

Aerodynamic Measures

Aerodynamic measures of voice include measures of air volume, air flow and sub glottal air pressure. The normal aerodynamic parameters of voice vary considerably among individuals, which leads to a large overlapping range of values between dysphonic and non-dysphonic patients. This limits the use of these measures as a diagnostic tool.^[15] Nonetheless, they are useful when used in adjunct with other voice assessment measures, or as a tool for monitoring therapeutic effects over time.^[18]

Treatment

A combination of both indirect and direct treatment methods are used to treat dysphonia.^{[8][11][21][22]}

Direct Therapies

Direct therapies address the physical aspects of vocal production.^[8] Techniques work to either modify vocal fold contact, manage breathing patterns, and/or change the tension at level of the larynx.^[8] Notable techniques include, but are not limited to, the yawn-sigh method, optimal pitch, laryngeal manipulation, humming, the accent method, and the Lee Silverman Voice Treatment.^[8][21] An example of a direct therapy is circumlaryngeal manual therapy, which has been used to reduce tension and massage hyoid-laryngeal muscles.^[11] This area is often tense from chronic elevation of the larynx.^[11] Pressure is applied to these areas as the patient hums or sustains a vowel.^[11] Traditional voice therapy is often used to treat muscular tension dysphonia.^[11]

Indirect Therapies

Indirect therapies take into account external factors that may influence vocal production.^[8] This incorporates maintenance of vocal hygiene practices, as well as the prevention of harmful vocal behaviours.^[23] Vocal hygiene includes adequate hydration of the vocal folds, monitoring the amount of voice use and rest, avoidance of vocal abuse (e.g., shouting, clearing of the throat), and taking into consideration lifestyle choices that may affect vocal health (e.g., smoking, sleeping habits).^[23] Vocal warm-ups and cool-downs may be employed to improve muscle tension and decrease risk of injury before strenuous vocal activities.^[23] It should be taken into account that vocal hygiene practices alone are minimally effective in treating dysphonia, and thus should be paired with other therapies.^[23]

Preventative Strategies

Given that certain occupations are more at risk for developing dysphonia (e.g. teachers) research into prevention studies have been conducted.^[24] Research into the effectiveness of prevention strategies for dysphonia have yet to produce definitive results, however, research is still ongoing.^[8][24] Primarily, there are two types of vocal training recognized by professionals to help with prevention: direct and indirect. Direct prevention describes efforts to reduce conditions that may serve to increase vocal strain (such as patient education, relaxation strategies, etc.), while indirect prevention strategies refer to changes in the underlying physiological mechanism for voice production (e.g. adjustments to the manner in which vocal fold adduction occurs, respiratory training, shifting postural habits, etc.).^[8][24]

Medical and Surgical Treatments

Medical and surgical treatments have been recommended to treat organic dysphonias. An effective treatment for spasmodic dysphonia (hoarseness resulting from periodic breaks in phonation due to hyperadduction of the vocal folds) is botulinum toxin injection.^[6][25] The toxin acts by blocking acetylcholine release at the thyro-arytenoid muscle. Although the use of botlinum toxin injections is considered relatively safe, patients' responses to treatment differ in the initial stages; some have reported experiencing swallowing problems and breathy voice quality as a side-effect to the injections.^[6][25] Breathiness may last for a longer period of time for males than females.^[25]

Surgeries involve myoectomies of the laryngeal muscles to reduce voice breaks, and laryngoplasties, in which laryngeal cartilage is altered to reduce tension.^[6]

Prevalence

Up to now, prevalence studies investigating rates of dysphonia on a large-scale level have been limited.^[3] According to a large sample of 55 million patients seeking health-care treatment in the United States, dysphonia can be found in approximately 1% of the population.^[3] Higher rates are reported in females and elderly adults, however, dysphonia can be found in both sexes and across age groups. It is proposed that higher rates in females are due to anatomical differences of the vocal mechanism.^[3]

Certain occupational groups may be more prone to developing voice disorders, namely dysphonia.^[4][5] Occupations that require extensive use of voice may be at a greater risk such as teachers and singers.^[5] However, the evidence is highly variable and must be interpreted carefully.^[4][5]

See also

• National Center for Voice and Speech
• Human voice
• Vocology
• Otorhinolaryngology#Laryngology
• Lists of language disorders

References

External links

• National Center for Voice and Speech's official website
• National Spasmodic Dysphonia Association
• ASHA: Voice Disorders
• ASHA: Clinical Topics- Voice Disorders Overview
• The Voice Foundation