Stroke-associated AOS is the most common form of acquired AOS, making up about 60% of all reported acquired AOS cases. This is one of the several possible disorders that can result from a stroke, but only about 11% of stroke cases involve this disorder. Brain damage to the neural connections, and especially the neural synapses, during the stroke can lead to acquired AOS. Most cases of stroke-associated AOS are minor, but in the most severe cases, all linguistic motor function can be lost and must be relearned. Since most with this form of AOS are at least fifty years old, few fully recover to their previous level of ability to produce speech.

Other disorders and injuries of the brain that can lead to AOS include (traumatic) dementia, progressive neurological disorders, and traumatic brain injury.

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."

Recent research has established the existence of primary progressive apraxia of speech caused by neuroanatomic motor atrophy. For a long time, this disorder was not distinguished from other motor speech disorders such as dysarthria and in particular primary progressive aphasia. Many studies have been done trying to identify areas in the brain in which this particular disorder occurs or at least to show that it occurs in different areas of the brain than other disorders. One study observed 37 patients with neurodegenerative speech disorders to determine whether or not it is distinguishable from other disorders, and if so where in the brain it can be found. Using speech and language, neurological, neuropsychological and neuroimaging testing, the researchers came to the conclusion that PAS does exist and that it correlates to superior lateral premotor and supplementary motor atrophy. However, because PAS is such a rare and recently discovered disorder, many studies do not have enough subjects to observe to make data entirely conclusive.

Developmental verbal dyspraxia is a developmental inability to motor plan volitional movement for the production of speech in the absence of muscular weakness. Research has suggested links to the FOXP2 gene.

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

DVD/CAS is a motor disorder, which means that the problem is located in the brain and its signals, and not in the mouth. In most cases, the cause is unknown. Possible causes include genetic syndromes and disorders.

Recent research has focused on the significance of the FOXP2 gene in both species and individual development.

Research regarding the KE family, where half the members of the extended family, over three generations, exhibited heritable developmental verbal dyspraxia, were found to have a defective copy of the FOXP2 gene. and further studies suggest that the FOXP2 gene as well as other genetic issues could explain DVD/CAS. including 16p11.2 microdeletion syndrome.

Birth/prenatal injuries, as well as stroke, can also be causes of DVD/CAS. Furthermore, DVD/CAS can occur as a secondary characteristic to a variety of other conditions. These include autism, some forms of epilepsy, fragile X syndrome, galactosemia, and chromosome translocations involving duplications or deletions.

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.

There are three significant features that differentiate DVD/CAS from other childhood speech sound disorders. These features are:

- "Inconsistent errors on consonants and vowels in repeated productions of syllables and words

- Lengthened coarticulatory transitions between sounds and syllables

- Inappropriate prosody, especially in the realization of lexical or phrasal stress"

Even though DVD/CAS is a "developmental" disorder, it will not simply disappear when children grow older. Children with this disorder do not follow typical patterns of language acquisition and will need treatment in order to make progress.

A speech sound disorder is a speech disorder in which some speech sounds (called phonemes) in a child's (or, sometimes, an adult's) language are either not produced, not produced correctly, or are not used correctly. The term protracted phonological development is sometimes preferred when describing children's speech to emphasize the continuing development while acknowledging the delay.

Muteness or mutism () is an inability to speak, often caused by a speech disorder, hearing loss, or surgery. Someone who is mute may be so due to the unwillingness to speak in certain social situations.

Motor speech disorders are a class of speech disorders that disturb the body's natural ability to speak due to neurologic impairments. These neurologic impairments make it difficult for individuals with motor speech disorders to plan, program, control, coordinate, and execute speech productions. Disturbances to the individual's natural ability to speak vary in their etiology based on the integrity and integration of cognitive, neuromuscular, and musculoskeletal activities. Speaking is an act dependent on thought and timed execution of airflow and oral motor / oral placement of the lips, tongue, and jaw that can be disrupted by weakness in oral musculature (dysarthria) or an inability to execute the motor movements needed for specific speech sound production (apraxia of speech or developmental verbal dyspraxia). Such deficits can be related to pathology of the nervous system (central and /or peripheral systems involved in motor planning) that affect the timing of respiration, phonation, prosody, and articulation in isolation or in conjunction.

Dysarthria is a motor speech disorder resulting from neurological injury of the motor component of the motor-speech system and is characterized by poor articulation of phonemes. In other words, it is a condition in which problems effectively occur with the muscles that help produce speech, often making it very difficult to pronounce words. It is unrelated to problems with understanding language (that is aphasia), although a person can have both. Any of the speech subsystems (respiration, phonation, resonance, prosody, and articulation) can be affected, leading to impairments in intelligibility, audibility, naturalness, and efficiency of vocal communication. Dysarthria that has progressed to a total loss of speech is referred to as anarthria.

Neurological injury due to damage in the central or peripheral nervous system may result in weakness, paralysis, or a lack of coordination of the motor-speech system, producing dysarthria. These effects in turn hinder control over the tongue, throat, lips or lungs; for example, swallowing problems (dysphagia) are also often present in those with dysarthria.

Dysarthria does not include speech disorders from structural abnormalities, such as cleft palate, and must not be confused with apraxia of speech, which refers to problems in the planning and programming aspect of the motor-speech system. Just as the term "articulation" can mean either "speech" or "joint movement", so is the combining form of the same in the terms "dysarthria", "dysarthrosis", and "arthropathy"; the term "dysarthria" is conventionally reserved for the speech problem and is not used to refer to arthropathy, whereas "dysarthrosis" has both senses but usually refers to arthropathy.

Cranial nerves that control the muscles relevant to dysarthria include the trigeminal nerve's motor branch (V), the facial nerve (VII), the glossopharyngeal nerve (IX), the vagus nerve (X), and the hypoglossal nerve (XII). The term is from New Latin, "dys-" "dysfunctional, impaired" and "arthr-" "joint, vocal articulation")

Pressured speech may also lead to the development of a stutter. The person's need or pressure to speak causes them to involuntarily stutter. Therefore, the person's need to express themselves is greater than their ability to vocalise their thoughts.

Those who are physically mute may have problems with the parts of the human body required for human speech (the esophagus, vocal cords, lungs, mouth, or tongue, etc.).

Trauma or injury to Broca's area, located in the left inferior frontal cortex of the brain, can cause muteness.

The exact cause of palilalia is unknown.

Palilalia also occurs in a variety of neurodegenerative disorders, occurring most commonly in Tourette syndrome, Alzheimer's disease, and progressive supranuclear palsy. Such degradation can occur in the substantia nigra where decreased dopamine production results in a loss of function. It can also occur in a variety of genetic disorders including Fragile X syndrome, Prader-Willi syndrome, Asperger's syndrome, autism, and the speaker has no difficulty initiating speech.

Most speech sound disorders occur without a known cause. A child may not learn how to produce sounds correctly or may not learn the rules of speech sounds on his or her own. These children may have a problem with speech development, which does not always mean that they will simply outgrow it by themselves. Many children do develop speech sounds over time but those who do not often need the services of a Speech-Language Pathologist to learn correct speech sounds.

Some speech sound errors can result from other syndromes or disorders such as:

- developmental disorders (e.g. autism)

- genetic disorders (e.g. Down syndrome)

- hearing loss, including temporary hearing loss, such as from ear infections

- cleft palate or other physical anomalies of the mouth

- illness

- neurological disorders (e.g. cerebral palsy)

Speech delay, also known as alalia, refers to a delay in the development or use of the mechanisms that produce speech. Speech, as distinct from language, refers to the actual process of making sounds, using such organs and structures as the lungs, vocal cords, mouth, tongue, teeth, etc. Language delay refers to a delay in the development or use of the knowledge of language.

Because language and speech are two independent stages, they may be individually delayed. For example, a child may be delayed in speech (i.e., unable to produce intelligible speech sounds), but not delayed in language. In this case, the child would be attempting to produce an age appropriate amount of language, but that language would be difficult or impossible to understand. Conversely, since a child with a language delay typically has not yet had the opportunity to produce speech sounds, it is likely to have a delay in speech as well.

Speech disorders or speech impediments are a type of communication disorder where 'normal' speech is disrupted. This can mean stuttering, lisps, etc. Someone who is unable to speak due to a speech disorder is considered mute.

At times, speech delay and impairment is caused by a physical disruption in the mouth such as a deformed frenulum, lips, or palate. If the motion or ability to form words and appropriate sounds is disrupted, the child may be slow to pick up words and lack the ability to shape their mouth and tongue in the formation of words.

Other more serious concerns are those that can be caused by oral-motor issues. Oral-motor dysfunction refers to a lack or delay in the area of the brain that speech is formed and created and communicated to the mouth and tongue. While speech may be the only concern, this disorder can be highlighted with feeding issues as well.

Children that are having speech delay disorders could have the following characteristics (Shriberg 1982):

- Speech mechanism in which speech is associated with hearing, motor speech and craniofacial malfunction

- Cognitive-linguistic aspects in which the impairment is associated with the child's intellectual, receptive, expressive and linguistic ability.

- Psychosocial issues in which the impairment is associated with caregiver, school environment, and the child's self behaviors such as aggression and maturity

The many other causes of speech delay include bilingual children with phonological disorders autism spectrum disorders, childhood apraxia, Auditory processing disorder, prematurity, cognitive impairment and hearing loss. Broomfield and Dodd's (2004a) found out after survey that 6.4% of children who are perfectly normal showed speech difficulty while they lacked these disorders will often show early signs and are at times identified as "at risk" when the speech delay is diagnosed.

Scanning speech, like other ataxic dysarthrias, is a symptom of lesions in the cerebellum. It is a typical symptom of multiple sclerosis, and it constitutes one of the three symptoms of Charcot's neurologic triad.

Scanning speech may be accompanied by other symptoms of cerebellar damage, such as gait, truncal and limb ataxia, intention tremor, inaccuracies in rapidly repeated movements and sudden, abrupt nausea and vomiting. The handwriting of such patients may also be abnormally large.

Tachylalia can occur with the following:

- Normal speech

- Cluttering

- Parkinson's disease

- Cluttered speech

- Pressure of speech

Scanning speech, also known as explosive speech, is a type of ataxic dysarthria in which spoken words are broken up into separate syllables, often separated by a noticeable pause, and spoken with varying force. The sentence "Walking is good exercise", for example, might be pronounced as "Walk (pause) ing is good ex (pause) er (pause) cise". Additionally, stress may be placed on unusual syllables.

The name is derived from literary scansion, because the speech pattern separates the syllables in a phrase much like scanning a poem counts the syllables in a line of poetry.

There is no universal agreement about the exact definition of this term. Some sources require only a noticeable pause between syllables, while others require other speech abnormalities, such as the unusual stress pattern on syllables. Some sources consider it a common, but not necessary, feature of ataxic dysarthria; others consider it exactly synonymous with ataxic dysarthria.

In relation to other types of aphasia, TMoA occurs less frequently, so there is less information on its prognosis. In general, for individuals with aphasia, most recovery is seen within 6 months of the stroke or injury although more recovery may continue in the following months or years. The timeline of recovery may look different depending on the type of stroke that caused the aphasia. With an ischemic stroke, recovery is greatest within the first two weeks and then diminishes overtime until the progress stabilizes. With a hemorrhagic stroke, the patient often shows little improvement in the first few weeks and then has relatively rapid recovery until they stabilize.

In a study involving eight patients with border zone lesions, all patients presented with transcortical mixed aphasia initially after the stroke. Three of these patients made a complete recovery within a few days post-stroke. For three other patients with more anterior lesions, their aphasia transitioned to TMoA. All participants in the study regained full language abilities within 18 months following their stroke. This suggests a positive long-term prognosis for patients with TMoA. However, this might not be the case for all patients and more research is needed in order to solidify these findings. Another study found that prognosis of TMoA is affected by lesion size. Smaller lesions typically cause delays in speech initiation; whereas, larger lesions lead to more profound language abnormalities and difficulty with abstract language abilities.

Research has shown that treatment has a direct effect on aphasia outcomes. Intensity, duration and timing of treatment all need to be taken in to consideration when choosing a course of treatment and determining a prognosis. In general, greater intensity leads to greater improvement. For duration, longer-term treatment produces more permanent changes. As for timing, beginning treatment too early may be difficult for the system which has not recovered enough to do intensive therapy, but beginning too late may result missing the window of the opportunity in which the most change can occur. Neuroplasticity, the brain's natural ability to reorganize itself following a traumatic event, occurs best when treatment connects simultaneous events, maintains attention, taps into positive emotion, utilizes repetition tasks, and is specific to the individual's needs.

Other factors affecting prognosis includes location and site of lesion. Since the lesion that results in TMoA usually occurs in the watershed area and does not directly involve the areas of the brain responsible for general language abilities, prognosis for these patients is good overall. Other factors that determine a patient’s prognosis include age, education prior to the stroke, gender, motivation, and support.

Tachylalia or tachylogia is extremely rapid speech. Tachylalia occurs in many clutterers and many people who have speech disorders.

Tachylalia is a generic term for speaking fast, and does not need to coincide with other speech problems. Tachylalia by itself is not considered a speech disorder.

Tachylalia may be exhibited as a single stream of rapid speech without prosody, and can be delivered quietly or mumbled. Tachylalia can be simulated by stimulating the brain electronically.

Cluttering (also called tachyphemia or tachyphrasia) is a speech and communication disorder characterized by a rapid rate of speech, erratic rhythm, and poor syntax or grammar, making speech difficult to understand.