Up to now, prevalence studies investigating rates of dysphonia on a large-scale level have been limited. 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. 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.

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

A hoarse voice, also known as hoarseness or dysphonia, is when the voice involuntarily sounds breathy, raspy, or strained, or is softer in volume or lower in pitch. It can be associated with a feeling of unease or scratchiness in the throat. Hoarseness is often a symptom of problems in the vocal folds of the larynx. It may be caused by laryngitis, which in turn may be caused by an upper respiratory infection, a cold, or allergies. Cheering at sporting events, speaking loudly in noisy situations, talking for too long without resting your voice, singing loudly, or speaking with a voice that's too high or too low can also cause temporary hoarseness. A number of other causes for losing one's voice exist, and treatment is generally by resting the voice and treating the underlying cause. If the cause is misuse or overuse of the voice drinking plenty of water may alleviate the problems.

It appears to occur more commonly in females and the elderly. Furthermore, certain occupational groups, such as teachers and singers, are at increased risk.

Long-term hoarseness, or hoarseness that persists over three weeks, especially when not associated with a cold or flu should be assessed by a medical doctor. It is also recommended to see a doctor if hoarseness is associated with coughing up blood, difficulties swallowing, a lump in the neck, pain when speaking or swallowing, difficulty breathing, or complete loss of voice for more than a few days. For voice to be classified as "dysphonic", abnormalities must be present in one or more vocal parameters: pitch, loudness, quality, or variability. Perceptually, dysphonia can be characterised by hoarse, breathy, harsh, or rough vocal qualities, but some kind of phonation remains.

Dysphonia can be categorized into two broad main types: organic and functional. The type of dysphonia is dependent on the 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.

Although the exact cause of spasmodic dysphonia (i.e., laryngeal dystonia) is still unknown, epidemiological, genetic and neurological pathogenic factors have been proposed in recent research.

Risk factors include:

- Being female

- Being middle aged

- Having a family history of neurological diseases (e.g., tremor, dystonia, meningitis and other neurological diseases)

- Stressful events

- Upper respiratory tract infections

- Sinus and throat illnesses

- Heavy voice use

- Cervical dystonia

- Childhood measles or mumps

- Pregnancy and parturition

It has not been established whether these factors directly impact the development of spasmodic dysphonia (SD), however these factors could be used to identify possible and/or at-risk patients.

Researchers have also explored the possibility of a genetic component to SD. Three genes have been identified that may be related to the development of focal or segmental dystonia: TUBB4A, THAP1 and TOR1A genes. However, a recent study that examined the mutation of these three genes in 86 SD patients found that only 2.3% of the patients had novel/rare variants in THAP1 but none in TUBB4A and TOR1A. Evidence of a genetic contribution for dystonia involving the larynx is still weak and more research is needed in order to establish a causal relationship between SD and specific genes.

SD is a neurological disorder rather than a disorder of the larynx, and as in other forms of dystonia, interventions at the end organ (i.e., larynx) have not offered a definitive cure, only symptomatic relief. The pathophysiology underlying dystonia is becoming better understood as a result of discoveries about genetically based forms of the disorder, and this approach is the most promising avenue to a long-term solution.

SD is classified as a neurological disorder. However, because the voice can sound normal or near normal at times, some practitioners believe it to be psychogenic, that is, originating in the affected person's mind rather than from a physical cause. No medical organizations or groups take this position. A comparison of SD patients compared with vocal fold paralysis (VFP) patients found that 41.7% of the SD patients met the DSM-IV criteria for psychiatric comorbidity compared with 19.5% of the VFP group. However, another study found the opposite, with SD patients having significantly less psychiatric comorbidity compared to VFP patients: "The prevalence of major psychiatric cases varied considerably among the groups, from a low of seven percent (1/14) for spasmodic dysphonia, to 29.4 percent (5/17) for functional dysphonia, to a high of 63.6 percent (7/11) for vocal cord paralysis." A review in the journal Swiss Medicine Weekly states that "Psychogenic causes, a 'psychological disequilibrium', and an increased tension of the laryngeal muscles are presumed to be one end of the spectrum of possible factors leading to the development of the disorder". Alternatively, many investigators into the condition feel that the psychiatric comorbidity associated with voice disorders is a result of the social isolation and anxiety that patients with these conditions feel as a consequence of their difficulty with speech, as opposed to the cause of their dysphonia. The opinion that SD is psychogenic is not upheld by experts in the scientific community.

SD is formally classified as a movement disorder, one of the focal dystonias, and is also known as laryngeal dystonia.

Injuries are often the cause of aphonia . Minor injuries can affect the second and third dorsal area in such a manner that the lymph patches concerned with coordination become either atrophic or relatively nonfunctioning. Tracheotomy can also cause aphonia.

Any injury or condition that prevents the vocal cords, the paired bands of muscle tissue positioned over the trachea, from coming together and vibrating will have the potential to make a person unable to speak. When a person prepares to speak, the vocal folds come together over the trachea and vibrate due to the airflow from the lungs. This mechanism produces the sound of the voice. If the vocal folds cannot meet together to vibrate, sound will not be produced. Aphonia can also be caused by and is often accompanied by fear.

Aphonia is defined as the inability to produce voiced sound. A primary cause of aphonia is bilateral disruption of the recurrent laryngeal nerve, which supplies nearly all the muscles in the larynx. Damage to the nerve may be the result of surgery (e.g., thyroidectomy) or a tumor.

Aphonia means "no sound". In other words, a person with this disorder has lost his/her voice.

There are a number of proposed causes for the development of puberphonia. The aetiology of puberphonia can be both organic (biological) or psychogenic (psychological) in nature. In males, however, organic causes are rare and psychogenic causes are more common.

Psychogenic causes of Puberphonia include:

- Emotional stress

- Delayed development of secondary sex characteristics

- Self-consciousness resulting from an early breaking of the voice

Organic causes of Puberphonia include:

- Laryngeal muscle tension which then causes laryngeal elevation

- Muscle Incoordination

- Congenital anomalies of the larynx

- Vocal fold asymmetries

- Unilateral vocal fold paralysis

- Non fusion of the thyroid laminae. When this is the case, it is important that hypogonadism is ruled out, as this may be the cause.

Puberphonia is described as having three main variants, related to the level of anatomical change. The most common presentation of the condition is characterized by a normal adult larynx and an increased pitch due to the vocal folds adopting the falsetto position. A second variant can occur when the laryngeal development is prolonged during puberty. Lastly, puberphonia can occur due to an incomplete transformation of the larynx into the adult form.

The presbylarynx is a condition in which age-related atrophy of the soft tissues of the larynx results in weak voice and restricted vocal range and stamina. In other words, it is the loss of vocal fold tone and elasticity due to aging which affects voice quality.

During puberty, changes in the larynx typically result in a decrease in pitch in both males and females. On average, the male voice deepens by one octave while the female voice lowers by a few semitones. The fundamental frequency (pitch) of an adult female typically falls between 165 and 255 Hz and an adult male between 85 and 180 Hz. Anatomical changes during puberty include enlargement of the larynx for both sexes. However, the larynx descends and grows significantly larger in males which often results in a visible laryngeal prominence on the neck (Adam’s Apple). Additionally, male vocal folds become longer and thicker and resonant cavities become larger. These changes contribute to a deepening of the voice characteristic of pubescent males.

Puberphonia is characterized by the failure to transition into the lower pitched voice of adulthood. In conjunction with an atypically high pitch, common symptoms include a weak, breathy, or hoarse voice as well as a low vocal intensity, pitch breaks, and shallow breathing.

Hypernasal speech (also hyperrhinolalia or open nasality; medically known as Rhinolalia aperta from Latin "rhinolalia": "nasal speech" and "aperta": "open") is a disorder that causes abnormal resonance in a human's voice due to increased airflow through the nose during speech. It is caused by an open nasal cavity resulting from an incomplete closure of the soft palate and/or velopharyngeal sphincter. In normal speech, nasality is referred to as nasalization and is a linguistic category that can apply to vowels or consonants in a specific language. The primary underlying physical variable determining the degree of nasality in normal speech is the opening and closing of a velopharyngeal passageway between the oral vocal tract and the nasal vocal tract. In the normal vocal tract anatomy, this opening is controlled by lowering and raising the velum or soft palate, to open or close, respectively, the velopharyngeal passageway.

Patulous Eustachian tube is a physical disorder. The exact causes may vary depending on the person. Weight loss is a commonly cited cause of the disorder due to the nature of the Eustachian tube itself. Fatty tissues hold the tube closed most of the time in healthy individuals. When circumstances cause overall body fat to diminish, the tissue surrounding the Eustachian tube shrinks and this function is disrupted.

Activities and substances which dehydrate the body have the same effect and are also possible causes of patulous Eustachian tube. Examples are stimulants (including caffeine) and exercise. Exercise may have a more short-term effect than caffeine or weight loss in this regard.

Pregnancy can also be a cause of patulous Eustachian tube due to the effects of pregnancy hormones on surface tension and mucus in the respiratory system.

Granulomatosis with polyangiitis can also be a cause of this disorder. It is yet unknown why.

Diplophonia, also known as diphthongia, is a phenomenon in which a voice is perceived as being produced with two concurrent pitches. Diplophonia is a result of vocal fold vibrations that are quasi-periodic in nature. It has been reported from old days, but there are no uniform interpretation of established mechanisms. It has been established that diplophonia can be caused by various vocal fold pathologies, such as vocal folds polyp, vocal fold nodule, recurrent laryngeal nerve paralysis or vestibular fold hypertrophy.

In most cases the cause is unknown. However, there are various known causes of speech impediments, such as "hearing loss, neurological disorders, brain injury, intellectual disability, drug abuse, physical impairments such as cleft lip and palate, and vocal abuse or misuse."

The list of treatments mentioned in various sources for presbylarynx includes the following list. Always seek professional medical advice about any treatment or change in treatment plans.

- Voice therapy

Patulous Eustachian Tube (PET) or tube to open remains an ET dysfunction category, difficult to diagnose and to treat. Recent studies suggest that the pathophysiology and etiology of PET is more related to a previous history of otitis media, rather than from weight loss, which was widely recognized as the major causal factor. Simultaneous weight gain can even be observed in some cases. The average age is 30 years, with a female prevalence. It’s rare to find patients of less than 15 years of age, which seems to confirm the opinion that PET is an acquired condition. Chronic upper respiratory inflammatory diseases are almost always associated with PET; half of these patients report previous history of nasal or sinus surgery. Radical posterior / inferior turbinectomies seem to be proportionally connected to PET severity. History of recurrent otitis media with effusion, with tympanostomy and adenoidectomy during childhood is also frequent. Laryngopharyngeal reflux (LPR) is identified in a great proportion of patients. Last epidemiological data indicates that PET results from obstructive ET dysfunction evolving over a long period of time.

Since the surgical management of these two pathologies is at diametrically opposed extremes, it is critical to obtain the correct diagnosis before undertaking any treatment. Visualization of a permanently open tubal valve by endoscopic examination allows settling this question, but its absence does not exclude PET diagnosis. Sonotubometry and recently developed tubomanometry may help in some specific cases. Unfortunately, some PET cases remain difficult to diagnose.

A number of operations that cut one of the nerves of the vocal folds (the recurrent laryngeal nerve) has improved the voice of many for several months to several years but the improvement may be temporary.

An operation called "selective laryngeal adductor denervation-rennervation (SLAD-R)" is effective specifically for adductor spasmodic dysphonia which has shown good outcomes in about 80% of people at 8 years. Post-surgery voices can be imperfect and about 15% of people have significant difficulties. If symptoms do recur this is typically in the first 12 months. Another operation called "recurrent laryngeal nerve avulsion" has positive outcomes of 80% at three years.

Another surgical option is a thyroplasty, which ultimately changes the position or length of the vocal folds. After thyroplasty there is an increase in both objective and subjective measures of speech.

The general term for disorders of the velopharyngeal valve is velopharyngeal dysfunction (VPD). It includes three subterms: velopharyngeal insufficiency, velopharyngeal inadequacy, and velopharyngeal mislearning.

- Velopharyngeal insufficiency can be caused by an anatomical abnormality of the throat. It occurs in children with a history of cleft palate or submucous cleft, who have short or otherwise abnormal vela. Velopharyngeal insufficiency can also occur after adenoidectomy.

- Velopharyngeal incompetence is a defective closure of the velopharyngeal valve due to its lack of speed and precision. It is caused by a neurologic disorder or injury (e.g. cerebral palsy or traumatic brain injury).

- Sometimes children present no abnormalities yet still have hypernasal speech: this can be due to velopharyngeal mislearning, indicating that the child has been imitating or has never learned how to use the valve correctly.

In 2006, the U.S. Department of Education indicated that more than 1.4 million students were served in the public schools' special education programs under the speech or language impairment category of IDEA 2004. This estimate does not include children who have speech/language problems secondary to other conditions such as deafness; this means that if all cases of speech or language impairments were included in the estimates, this category of impairment would be the largest. Another source has estimated that communication disorders—a larger category, which also includes hearing disorders—affect one of every 10 people in the United States.

ASHA has cited that 24.1% of children in school in the fall of 2003 received services for speech or language disorders—this amounts to a total of 1,460,583 children between 3 –21 years of age. Again, this estimate does not include children who have speech/language problems secondary to other conditions. Additional ASHA prevalence figures have suggested the following:

- Stuttering affects approximately 4% to 5% of children between the ages of 2 and 4.

- ASHA has indicated that in 2006:

- Almost 69% of SLPs served individuals with fluency problems.

- Almost 29% of SLPs served individuals with voice or resonance disorders.

- Approximately 61% of speech-language pathologists in schools indicated that they served individuals with SLI

- Almost 91% of SLPs in schools indicated that they servedindividuals with phonological/articulation disorder

- Estimates for language difficulty in preschool children range from 2% to 19%.

- Specific Language Impairment (SLI) is extremely common in children, and affects about 7% of the childhood population.

Voice disorders are medical conditions involving abnormal pitch, loudness or quality of the sound produced by the larynx and thereby affecting speech production. These include:

- Puberphonia

- Chorditis

- Vocal fold nodules

- Vocal fold cysts

- Vocal cord paresis

- Reinke's edema

- Spasmodic dysphonia

- Foreign accent syndrome

- Bogart–Bacall syndrome

- Laryngeal papillomatosis

- Laryngitis

Unilateral hearing loss (UHL) or single-sided deafness (SSD) is a type of hearing impairment where there is normal hearing in one ear and impaired hearing in the other ear.

Bogart–Bacall syndrome (BBS) is a voice disorder that is caused by abuse or overuse of the vocal cords.

People who speak or sing outside their normal vocal range can develop BBS; symptoms are chiefly an unnaturally deep or rough voice, or dysphonia, and vocal fatigue. The people most commonly afflicted are those who speak in a low-pitched voice, particularly if they have poor breath and vocal control. The syndrome can affect both men and women.

In 1988 an article was published, describing a discrete type of vocal dysfunction which results in men sounding like Humphrey Bogart and women sounding like Lauren Bacall. BBS is now the medical term for an ongoing hoarseness that often afflicts actors, singers or TV/radio voice workers who routinely speak in a very low pitch.

Treatment usually involves voice therapy by a speech language pathologist.

Dysprosody, which may manifest as pseudo-foreign accent syndrome, refers to a disorder in which one or more of the prosodic functions are either compromised or eliminated completely.

Prosody refers to the variations in melody, intonation, pauses, stresses, intensity, vocal quality, and accents of speech. As a result, prosody has a wide array of functions, including expression on linguistic, attitudinal, pragmatic, affective and personal levels of speech. People diagnosed with dysprosody most commonly experience difficulties in pitch or timing control. Essentially, people diagnosed with the disease can comprehend language and vocalize what they intend to say, however, they are not able to control the way in which the words come out of their mouths. Since dysprosody is the rarest neurological speech disorder discovered, not much is conclusively known or understood about the disorder. The most obvious expression of dysprosody is when a person starts speaking in an accent which is not their own. Speaking in a foreign accent is only one type of dysprosody, as the disease can also manifest itself in other ways, such as changes in pitch, volume, and rhythm of speech. It is still very unclear as to how damage to the brain causes the disruption of prosodic function. The only form of effective treatment developed for dysprosody is speech therapy.

Known causes include physical trauma, acoustic neuroma, measles, labyrinthitis, microtia, meningitis, Ménière's disease, Waardenburg syndrome, mumps (epidemic parotitis), and mastoiditis.

Many of these types of disorders can be treated by speech therapy, but others require medical attention by a doctor in phoniatrics. Other treatments include correction of organic conditions and psychotherapy.

In the United States, school-age children with a speech disorder are often placed in special education programs. Children who struggle to learn to talk often experience persistent communication difficulties in addition to academic struggles. More than 700,000 of the students served in the public schools’ special education programs in the 2000-2001 school year were categorized as having a speech or language impediment. This estimate does not include children who have speech and language impairments secondary to other conditions such as deafness". Many school districts provide the students with speech therapy during school hours, although extended day and summer services may be appropriate under certain circumstances.

Patients will be treated in teams, depending on the type of disorder they have. A team can include SLPs, specialists, family doctors, teachers, and family members.

Dysprosody is usually attributed to neurological damage, such as brain tumors, brain trauma, brain vascular damage, stroke and severe head injury. To better understand the causes of the disease, 25 cases of dysprosody diagnosed between 1907-1978 were examined more closely. It was found that the majority developed dysprosody after a cerebrovascular accident, while another 6 cases developed after a head trauma. In that same study, 16 of the patients were female, while 9 were male. However, there has been no conclusive evidence that gender affects the onset of dysprosody. There has been no evidence that ethnicity, age, or genetics has any impact on the development of dysprosody.

In another reported case in 2004, a patient presented with dysprosody under interesting circumstances. The patient underwent surgery to correct a Reinke's edema, which originates in the vocal folds of the larynx. After the surgery, however, she began speaking in a foreign German accent. Neurological examinations were carried out on the patient through magnetic resonance imaging, but the results were completely normal. The only conclusion the doctors could make was that the surgery somehow changed the patient's vocal identification causing the new voice pattern. It was possible that the patient suffered a lack of oxygen to the brain during the surgery, which would have gone undetected by the resonance imaging, causing dysprosody. Although most causes of dysprosody are due to neurological damage, this case study shows that there can be other causes which are not necessarily neurologically based.

There are many potential causes of dysarthria. They include toxic, metabolic, degenerative diseases, traumatic brain injury, or thrombotic or embolic stroke.

Degenerative diseases include parkinsonism, amyotrophic lateral sclerosis (ALS), multiple sclerosis, Huntington's disease, Niemann-Pick disease, and Friedreich ataxia.

Toxic and metabolic conditions include: Wilson's disease, hypoxic encephalopathy such as in drowning, and central pontine myelinolysis.

These result in lesions to key areas of the brain involved in planning, executing, or regulating motor operations in skeletal muscles (i.e. muscles of the limbs), including muscles of the head and neck (dysfunction of which characterises dysarthria). These can result in dysfunction, or failure of: the motor or somatosensory cortex of the brain, corticobulbar pathways, the cerebellum, basal nuclei (consisting of the putamen, globus pallidus, caudate nucleus, substantia nigra etc.), brainstem (from which the cranial nerves originate), or the neuro-muscular junction (in diseases such as myasthenia gravis) which block the nervous system's ability to activate motor units and effect correct range and strength of movements.

Causes:

- Brain tumor

- Cerebral palsy

- Guillain–Barré syndrome

- Hypothermia

- Lyme disease

- Stroke

- Intracranial hypertension (formerly known as pseudotumor cerebri)

- Tay-Sachs, and late onset Tay-Sachs (LOTS), disease