Apraxia is a disorder caused by damage to specific areas of the cerebrum. Apraxia is characterized by loss of the ability to execute or carry out learned purposeful movements, despite having the desire and the physical ability to perform the movements. It is a disorder of motor planning, which may be acquired or developmental, but may not be caused by incoordination, sensory loss, or failure to comprehend simple commands (which can be tested by asking the person to recognize the correct movement from a series). Apraxia should not be confused with ataxia, a lack of coordination of movements, aphasia, an inability to produce and/or comprehend language; abulia, the lack of desire to carry out an action; or allochiria, in which patients perceive stimuli to one side of the body as occurring on the other.
There are many different forms of apraxia. Some are listed below:
- Buccofacial or orofacial apraxia. Difficulty carrying out movements of the face on demand. For example, an inability to lick one’s lips or whistle.
- Ideational apraxia. Loss of ability to carry out learned complex tasks in the proper order, such as putting on socks before putting on shoes.
- Ideomotor apraxia. Loss of ability to voluntarily perform a learned task when given the necessary objects. For instance, if given a screwdriver, the patient may try to write with it as if it were a pen, or try to comb one’s hair with a toothbrush.
- Limb-kinetic apraxia. Difficulty making precise movements with an arm or leg.
- Verbal apraxia. Trouble coordinating mouth movements and speech.
Apraxia of Speech (AOS) is a motor speech disorder affecting an individual’s ability to translate conscious speech plans into motor plans and is caused by illness or injury in adults. Like other apraxias, it only affects volitional movement patterns. In children, Childhood Apraxia of Speech, Dyspraxia of speech, verbal apraxia, and other terms, are used to describe difficulty in planning and programming speech movements.
Childhood Apraxia of Speech
Childhood Apraxia of Speech (CAS) is the term used most widely to describe difficulty in planning and programming speech movements in children. CAS is considered to be a neurological speech disorder that can occur by itself, along with other neuro-developmental disorders (such as autism, mitochondrial disorders, Down Syndrome, etc.), or due to accident or illness. CAS can range from mild to very severe. Children with apraxia of speech, in early stages of speech development, are likely to need intensive, individual, and frequent speech therapy in order to become intelligible speakers. According to the Childhood Apraxia of Speech Association of North America, with proper help, children with apraxia of speech can make great strides in speech, language and communication with appropriate help, and in many cases they can achieve progress to the point that no one could tell that they had a severe speech disorder. However, often, other speech, language, and learning difficulties co-occur with this speech disorder.
Stroke-associated AOS is the most common form of AOS with about 60% of all AOS cases reported. 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 leads to this disorder. 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-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 last 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.
Nature and Symptoms
Sufferers of AOS have impaired prosody, which causes their speech to be slow, highly segmented (at the syllable or word level), and is often described as ‘robotic’. Because of this, they also exhibit equal syllabic stress (tec-ton-ic as opposed to tec-TON-ic), and have trouble consciously producing correct stress patterns, even though they are aware of prosodic patterns required.
Symptoms are evident only in connected speech.
AOS is often associated with Broca’s Aphasia. It is actually characterised by damage to the posterior portion of Broca’s area; the insula, an area underneath the inferior-anterior portion of the temporal lobe, concealed by the fissure separating the frontal and temporal lobes; and the lentiform nucleus. However, some studies have shown that only a percentage of patients with AOS have these lesions.
Acquired 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 errors. Coexisting characteristics may include groping and effortful speech production with self-correction, difficulty initiating speech, abnormal stress, intonation and rhythm, and inconsistency with articulation errors.
Wertz et al, (1984) describe the following as speech characteristics that an individual with apraxia of speech can exhibit:
1) Effortful trial and error with groping 2) Self correction of errors 3) Abnormal rhythm, stress and intonation 4) Inconsistent articulation errors on repeated speech productions of the same utterance 5) Difficulty initiating utterance
Differential diagnosis is important as AOS can co-occur with a Broca’s Aphasia (Duffy, 1995), appear to have similar speech sound level errors as in conduction aphasia and may share the appearance of a dysarthria. Individual’s with Broca’s aphasia will also have linguistic deficits to include naming difficulties and agrammatism. Similarly, individuals with Conduction aphasia have an underlying language deficit prohibiting their ability to select the correct phonemes and typically lack the awareness of their errors. This is in contrast to AOS in which it is believed the individual chooses the correct phoneme, however the motor execution is disrupted and are more likely to make attempts at self-correction. Dysarthria is due to an impairment in the muscle tone, strength, range of motion and/or coordination of movement as a result of damage to the central or peripheral nervous system. Dysarthria is characterized by imprecise articulation, changes in resonance, prosody, phonation. The primary distinguishing diagnostic factor between dysarthria and AOS is the consistency and predictability of the sound errors. Speech errors found in individuals with AOS are inconsistent and irregular in contrast to the consistent and predictable errors found in individuals with dysarthria.