Excerpt from Apraxia and Related Syndromes

Synonyms, Key Words, and Related Terms: apraxia and related syndromes, behavioral neurology syndrome, apraxia of speech, buccofacial apraxia, callosal apraxia, conceptual apraxia, dyspraxia, ideomotor apraxia, ideational apraxia, limb apraxia, limb kinetic apraxia, magnetic apraxia, motor agnosia, oral apraxia, parectropia, disorder of voluntary movement, voluntary movement disorder, alien hand syndrome

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Background

Apraxia is one of the most important and least understood major behavioral neurology syndromes. It is one of the best localizing signs of the mental status examination and also predicts disability in patients with stroke or dementia (unlike aphasia). Patients with apraxia cannot use tools; therefore, they are unlikely to perform activities of daily living well. Patients with aphasia, without coexisting apraxia, can live independently, take the bus or subway, and lead a relatively normal life; a patient with significant limb apraxia is likely to remain dependent.

Heilman defined apraxia in negative terms, "Apraxia is defined as a disorder of skilled movement not caused by weakness, akinesia, deafferentation, abnormal tone or posture, movement disorders such as tremors or chorea, intellectual deterioration, poor comprehension, or uncooperativeness."¹ To simplify matters, apraxia can be considered a form of a motor agnosia. Patients are not paretic but have lost information about how to perform skilled movements.

There is no consensus on how to divide and organize the many different syndromes known as apraxias. Authors have divided apraxias based on the following:

Body part affected (eg, limb apraxia or buccofacial apraxia)
Dysfunctional sensory area (left inferior parietal) or motor areas (left premotor and left supplementary motor)
If use of tools is affected (transitive vs intransitive)
If knowledge about the use of tools is preserved (conceptual)
Deficits in pantomiming tool use and gesture (ideomotor)

The term apraxia is used to describe a variety of syndromes, including the following, which are not considered true apraxias by some.

Dressing apraxia - Usually associated with right parietal lesions and part of a neglect syndrome
Constructional apraxia - Inability to copy 2-dimensional drawings or 3-dimensional assemblies (may be associated with right or left parietal and left frontal among other brain regions)
Gait apraxia - Part of the triad of symptoms of normal pressure hydrocephalus
Gaze apraxia - Part of Balint syndrome
Apraxia of eyelid opening
Magnetic apraxia

Pathophysiology

Apraxia is a syndrome reflecting motor system dysfunction at the cortical level, exclusive of primary motor cortex. In planning movements, previously learned, stored complex representations of skilled movements are used. These 3-dimensional, supramodal codes, also called representations or movement formulae, are stored in the inferior parietal lobule of the left hemisphere. Diseases that involve this part of the brain, including strokes, dementias, and tumors, can cause loss of knowledge about how to perform skilled movements.

Apraxia can occur with lesions in other locations as well. Information contained in praxis representations is transcoded into innervatory patterns by the premotor cortices, including the supplementary motor area (SMA) and possibly the convexity of the premotor cortex; the information is then transmitted to the primary motor cortex and a movement is performed. Lesions of the SMA or other premotor cortices also can cause apraxia; in this case, knowledge about movement is still present, but the ability to perform movement is absent.

Apraxia also occurs with lesions of the corpus callosum, such as tumors or anterior cerebral artery strokes. Although the corpus callosum is not known to be involved directly in the performance of skilled movements, it contains crossing fibers from the right hemisphere to the premotor cortex. This type of apraxia represents a classic disconnection syndrome; patients with callosal apraxia typically are apractic only with the left hand.

Frequency

United States

Few data are available regarding the frequency of apraxia; however, it commonly occurs after stroke and in dementia—2 of the most frequent neurological illnesses.

International

Few data are available regarding the frequency of apraxia.

Mortality/Morbidity

Apraxia is not a disease but a syndrome; consequently, it has no attributable morbidity or mortality.

Race

No data are available.

Sex

No good data are available.

Age

No good data exist concerning the occurrence of apraxia in different age groups. However, it is more common in older age groups, as they typically have higher frequencies of stroke and dementia.

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