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Apraxia of Speech (AOS) is an oral motor speech disorder affecting an individual's ability to translate conscious speech plans into motor plans, which results in limited and difficult speech ability. In adults, the disorder is caused by illness or injury, while the cause of AOS in children is still unknown. Like other apraxias, AOS only affects volitional (willful or purposeful) movement patterns. Individuals with this disorder have difficulty connecting speech messages from the brain to the mouth.

The speech disorder, Apraxia of Speech, can be divided into two specific types: Acquired Apraxia of Speech (AOS) and Childhood Apraxia of Speech (CAS). Acquired Apraxia of Speech is a loss of prior speech ability resulting from a brain illness or injury which occurs in both children and adults. Childhood Apraxia of Speech is an inability to utilize motor planning to perform movements necessary for speech during a child's language learning process. Although the age of onset differs between the two forms, the main characteristics and treatments are similar. For the purpose of this article, both terms will be referred to as 'Apraxia of Speech (AOS).'

Characteristics
Apraxia of Speech (AOS) is a neurogenic communication disorder affecting the motor programming system for speech production. Individuals with AOS demonstrate difficulty in the speech production specifically with the sequencing and forming of sounds. The individual knows exactly what they want to say, however there is a disruption in the part of the brain that sends the signal to the muscle for the specific movement. Individuals with acquired AOS demonstrate hallmark characteristics of articulation and prosody (rhythm, stress or intonation) errors. Coexisting characteristics may include groping and effortful speech production with self-correction, difficulty initiating speech, abnormal stress, intonation and rhythm errors, and inconsistency with articulation.

Wertz et al, (1984) describe the following five speech characteristics that an individual with apraxia of speech may exhibit: Groping is when the mouth searches for the position needed to create a sound. When this trial and error process occurs, sounds may be held out longer, repeated or silently voiced. When one is consciously aware of the attempted speech movements, this is called volitional control. In some cases, one may be able to easily produce certain sounds on their own, unconsciously. Yet, when prompted by another to produce the same sound the patient may grope with their lips, using volitional control, while struggling to produce the sound.
 * Effortful trial and error with groping

Patients are aware of their speech errors and can attempt to correct themselves. This can involve distorted consonants, vowels, and sound substitutions. People with AOS often have a much greater understanding of speech compared to what they are able to express. This receptive ability allows them to attempt at self correction.
 * Self correction of errors

Sufferers of AOS present with prosodic errors which include irregular pitch, rate, and rhythm. This impaired prosody causes their speech to be: too slow or too fast and highly segmented (many pauses). An AOS speaker also stresses syllables incorrectly and sounds monotone. As a result, the speech is often described as 'robotic'. When words exhibit equal syllabic stress in a monotone manner, a word such as 'tectonic' may sound like 'tec-ton-ic' as opposed to 'tec-TON-ic'. These patterns occur even though the speakers are aware of the prosodic patterns that should be used.
 * Abnormal rhythm, stress and intonation

When producing the same utterance in different instances, a person with AOS may have difficulty using and maintaining the same articulation that was previously used for that utterance. Articulation also becomes more difficult when a word or phrase requires an articulation adjustment, in which the lips and tongue must move in order to shift between sounds. For example, the word "baby" needs less mouth adjustment than the word "dog" requires, since producing "dog" requires two tongue/lips movements to articulate.
 * Inconsistent articulation errors on repeated speech productions of the same utterance

Producing utterances becomes a difficult task in patients with AOS. The errors in completing a speech movement gesture increase as the length of the utterance increases. Since multisyllabic words are difficult, those with AOS use simple syllables and a limited range of consonants and vowels.
 * Difficulty initiating utterances

Diagnosis
Apraxia of speech can be diagnosed by a Speech Language Pathologist (SLP) through specific exams that measure oral mechanisms of speech. The exam involves tasks such as pursing lips, blowing, licking lips, elevating the tongues, and also involves an examination of the mouth, and observation of the patient eating and talking. Tests such as the Kaufman Speech Praxis test, a more formal examination, are also used in diagnosis. SLPs do not agree on a specific set of characteristics that make up the Apraxia of Speech diagnosis, so any of the characteristics from the section above could be used to form a diagnosis. For Acquired AOS, patients may be asked to perform other daily tasks such as reading, writing, and conversing with others. In situations involving brain damage, an MRI brain scan also helps determine damaged areas of the brain.

A differential diagnosis must be used in order to rule out other similar or alternative disorders. Although disorders such as Broca's aphasia, conduction aphasia, and dysarthria involve similar symptoms as Apraxia of Speech, we must distinguish between the disorders in order to correctly treat the patients. While apraxias involve the planning aspect of speech, aphasic disorders such as these involve the content of the language. A differential diagnosis of AOS is often not possible for children under the age of 2 years old. Even when children are between 2-3 years, a clear diagnosis cannot always occur because at this age, they may still be unable to focus on, or cooperate with, diagnostic testing.

AOS and Broca's aphasia (also known as Expressive Aphasia) are commonly mistaken as the same disorder mainly because they often occur together in patients. Although both disorders present with symptoms such as a difficulty producing sounds due to damage in the language parts of the brain, they are not the same. The main difference between these disorders lies in the ability to comprehend spoken language; patients with Apraxia are able to fully comprehend speech, while patients with Aphasia are not always fully able to comprehend others' speech.

Conduction Aphasia is another speech disorder that is similar to, but not the same as, Apraxia of Speech. Although Conduction Aphasia involves full comprehension of speech, like those with AOS, there are some differences between the two. Those with Conduction Aphasia are typically able to speak fluently, but they do not have the ability to repeat what they hear. Similarly, Dysarthria, another motor speech disorder, is characterized by difficulty articulating sounds. The difficulty in articulation does not occur due in the planning the motor movement, as AOS does. Instead, Dysarthria is caused by the inability or weakness of the muscles in the mouth, face, and respiratory system.

Cause of Childhood Apraxia of Speech (CAS)
The cause of CAS remains unknown at this point in the research on the disorder. Some speculators believe the disorder is associated with a child's overall language development, while others see it as a neurological disorder in which the brain is unable to send messages to the speech muscles. Research on the brain structures has not been able to find specific areas indicating lesions or differences in brain structure. Some observations suggest a genetic relationship with CAS, as many with the disorder have a family history of communication disorders.

Brain damage
AOS can be caused by any type of brain damage affecting the speech controls in the brain. Brain damage can occur as a result of stroke, head injury, tumor, or a specific illness affecting brain functioning.

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 lead to acquiring 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 state of linguistics.

Stress
Stress-induced AOS account for about 25% of all cases of AOS in the United States and Canada. This is the least severe of the forms and often lasts only a few weeks. It is marked by an inability to communicate effectively after overwhelming levels of unresolved stress. The three major sources of stress that induce this form of AOS are long drawn-out divorces, high-profile criminal cases, and incidences of extreme child abuse.

Treatment
In cases of Acquired AOS, spontaneous recovery may occur, in which previous speech abilities reappear on their own. All other cases of Acquired AOS and CAS require a form of therapy, however the therapy differs with the individual needs of the patient. Typically, treatment involves one-on-one therapy with a Speech Language Pathologist (SLP). For severe forms of AOS, therapy may start at 3-5 sessions per week, which is reduced with speech improvement. In children with CAS, consistency is a key element in treatment. Consistency in the form of communication, as well as the development and use of oral communication are extremely important in aiding a child's speech learning process. Another main theme in AOS treatment is the use of repetition in order to achieve a large amount of target utterances, or desired speech usages.

One treatment method, called the Motor-programming Approach, involves five essential key elements of treatment. The first is practicing desired speech targets with frequency and intensity. In order to achieve accuracy in speech movements, treatment must be fully focused on one particular skill at a time. Treatment should also include other sensory cues in addition to sound, such as sight and touch. The type of practice is another factor that should be kept in mind, such as whether the target items that are used are random or blocked. Finally, feedback to the patient is important in order to communicate results of their performance.

History & Terminology
The term Apraxia was first defined by Hugo Karl Liepmann in 1908 as the "inability to perform voluntary acts despite preserved muscle strength." In 1969, Frederic L. Darley initiated the term 'apraxia of speech,' replacing Liepmann's original term ‘apraxia of the glosso-labio-pharyngeal structures.’ Paul Broca had also identified this speech disorder in 1861, which he referred to as 'aphemia': a disorder involving difficulty of articulation despite having intact language skills and muscular function.

The disorder is currently referred to as 'apraxia of speech,' but was also formerly termed 'verbal dyspraxia.' The term apraxia comes from the Greek root “praxis,” meaning the performance of action or skilled movement. Adding the prefix 'a,' meaning absence, or 'Dys,' meaning partial, to the root 'praxis,' both function to imply speech difficulties related to movement.