Apraxia is a motor disorder caused by damage to the brain (specifically the posterior parietal cortex or corpus callosum), which causes difficulty with motor planning to perform tasks or movements. The nature of the damage determines the disorder's severity, and the absence of sensory loss or paralysis helps to explain the level of difficulty. Children may be born with apraxia; its cause is unknown, and symptoms are usually noticed in the early stages of development. Apraxia occurring later in life, known as acquired apraxia, is typically caused by traumatic brain injury, stroke, dementia, Alzheimer's disease, brain tumor, or other neurodegenerative disorders. The multiple types of apraxia are categorized by the specific ability and/or body part affected.
The term "apraxia" comes from the Greek ἀ- a- ("without") and πρᾶξις praxis ("action").
Types
The several types of apraxia include: Apraxia of speech (AOS) is having difficulty planning and coordinating the movements necessary for speech (e.g. potato=totapo, topato). AOS can independently occur without issues in areas such as verbal comprehension, reading comprehension, writing, articulation, or prosody. Buccofacial or orofacial apraxia, the most common type of apraxia, is the inability to carry out facial movements on demand. For example, an inability to lick one's lips, wink, or whistle when requested to do so. This suggests an inability to carry out volitional movements of the tongue, cheeks, lips, pharynx, or larynx on command. Constructional apraxia is the inability to draw, construct, or copy simple configurations, such as intersecting shapes. These patients have difficulty copying a simple diagram or drawing basic shapes. Gait apraxia is the loss of ability to have normal function of the lower limbs such as walking. This is not due to loss of motor or sensory functions. Ideational/conceptual apraxia is having an inability to conceptualize a task and impaired ability to complete multistep actions. This form of apraxia consists of an inability to select and carry out an appropriate motor program. For example, the patient may complete actions in incorrect orders, such as buttering bread before putting it in the toaster, or putting on shoes before putting on socks. Also, a loss occurs in the ability to voluntarily perform a learned task when given the necessary objects or tools. For instance, if given a screwdriver, these patients may try to write with it as if it were a pen, or try to comb their hair with a toothbrush. Ideomotor apraxia is having deficits in the ability to plan or complete motor actions that rely on semantic memory. These patients are able to explain how to perform an action, but unable to "imagine" or act out a movement such as "pretend to brush your teeth" or "pucker as though you bit into a sour lemon." When the ability to perform an action automatically when cued remains intact, though, this is known as automatic-voluntary dissociation. For example, they may not be able to pick up a phone when asked to do so, but can perform the action without thinking when the phone rings. Limb-kinetic apraxia is having the inability to perform precise, voluntary movements of extremities. For example, a person affected by limb apraxia may have difficulty waving hello, tying shoes, or typing on a computer. This type is common in patients who have experienced a stroke, some type of brain trauma, or have Alzheimer's disease. Oculomotor apraxia is having difficulty moving the eye on command, especially with saccade movements that direct the gaze to targets. This is one of the three major components of Balint's syndrome.
Causes
Apraxia is most often due to a lesion located in the dominant (usually left) hemisphere of the brain, typically in the frontal and parietal lobes. Lesions may be due to stroke, acquired brain injuries, or neurodegenerative diseases such as Alzheimer's disease or other dementias, Parkinson's disease, or Huntington's disease. Also, apraxia possibly may be caused by lesions in other areas of the brain.
Ideomotor apraxia is typically due to a decrease in blood flow to the dominant hemisphere of the brain and particularly the parietal and premotor areas. It is frequently seen in patients with corticobasal degeneration.
Ideational apraxia has been observed in patients with lesions in the dominant hemisphere near areas associated with aphasia, but more research is needed on ideational apraxia due to brain lesions. The localization of lesions in areas of the frontal and temporal lobes would provide explanation for the difficulty in motor planning seen in ideational apraxia, as well as its difficulty to distinguish it from certain aphasias.