Apraxia

Why Can't You Do What You Do?

Doctor
Doctor. Adam Berry / Stringer / Getty Images

The term apraxia has been applied to many, often seemingly unrelated disorders, and has been divided into several overlapping sub-categorizations. The result is that often even neurologists disagree about what they mean when they say "apraxia," and may argue about whether a particular symptom fits the definition. Most broadly, apraxia means in inability to perform a skilled movement despite intact strength, sensation, and other cognitive faculties such as attention, memory or drive.

Apraxia cannot be due to interfering movements such as tremor, dystonia or chorea, but instead reflects an inability to integrate the information required to perform a needed movement.

What Causes Apraxia?

Apraxia can result from lesions in several different regions of the brain, including parietal, frontal, and subcortical lesions. For some reason, however, apraxia almost always results from damage to the left hemisphere or to the bundle of fibers that connects the left and right hemisphere (the corpus callosum). Lesions such as tumors, stroke, or multiple sclerosis may lead to apraxia, and it is often seen in degenerative illnesses like Alzheimer's disease. Apraxia is a core feature of corticobasal syndrome as well.

Limb Kinetic Apraxia

There are several proposed subtypes of apraxia, of which limb kinetic, or ideomotor, apraxia is the most commonly agreed upon. Ideomotor apraxia means a loss of ability to perform a previously learned skilled movement.

This can impact any voluntary movement in the body, but has been best studied in the arms and hands. For example, someone with ideomotor apraxia may lose the ability to manipulate commonly used tools, or may describe the loss of ability to perform something more complex, such as sewing or knitting.

When asked to pantomime performing some activity, they may hold their hand in the wrong position, or move it in the wrong direction. Another common error is to substitute a body part as the tool, rather than pantomiming use of the tool as requested. For example, when asked to demonstrate how to use a toothbrush, they may instead brush their teeth with their finger, even when corrected and told to pretend they are holding the toothbrush.

Other Types of Apraxia

Apraxia has been subcategorized in several different fashions. Not all those apraxia types are universally recognized as being true apraxia, though.

Apraxia by Task Type

Some people classify apraxia by what daily task the apraxic person is no longer able to perform. For example, someone may no longer be able to dress properly, and so they would be said to have a dressing apraxia. Someone may no longer be able to draw something, and would be said to have a constructional apraxia. The problem is that there are other recognized neurological deficits that can lead to these disabilities.

For example, someone with a right parietal lobe stroke may lose their ability to perceive the left part of their world. This makes it difficult to get dressed, since they may not even recognize the left side of their body as their own. This is a problem with spatial recognition, though, not with performing a movement per se.

Apraxia by Body Part

Others refer to apraxia by body part. This can be both accurate and useful-if someone is unable to use their left leg appropriately, it can lead to important repercussions such as difficulty walking. Buccofacial apraxia means difficulty using the lips and mouth, which can interfere with speech. The term comes into contention, though, when referring to movements that do not require any degree of skill. For example, some people call an inability to open the eyelids an "eyelid apraxia," but this could in fact reflect a weakness or other disorder such as dystonia, thereby failing to meet the definition of apraxia, which requires no other explanatory movement disorder be present.

Apraxia by Severity

Apraxia can also be categorized by degree of severity. For example, in dissociation apraxia, the person cannot pantomime an action to command, but can still use the stated object if it is actually handed to them, and can imitate the examiner. In conduction apraxia, the person can neither pantomime nor imitate.

In ideational apraxia, a patient can perform simple individual actions, but cannot sequence them appropriately. For example, a patient with ideational apraxia could not pantomime pulling a match book out of their pocket, opening it to get a match, lighting the match, then blowing it out, but might instead mix up the order of these events.

This is perhaps the most widely agreed on way of discussing apraxia, but some debate still exists. For example, limb-kinetic apraxia is posited to be a very simple form of apraxia in which everything else discussed is intact, but the patient can no longer perform movements with deft coordination. There are so many other potential reasons that someone might be clumsy, including the rigidity of parkinsonism, that many doctors question the existence of limb-kinetic apraxia as a distinct entity.

Conclusion

Despite the disagreements among types of apraxia, some things remain consistent. Apraxia represents a lack of neural communication at some point in the brain. Even though part of the brain may understand what it is being asked to do, it cannot relay that information to the parts that coordinate the movement. These lines of communication can be disrupted in several places throughout the brain, making it difficult to reliably determine precisely where the problem arises, but can clue a doctor into doing additional tests to determine the apraxia's cause.

The brain is good at rewiring itself, and provided time and protection from further injury, can reroute that neural information to become better coordinated again. Physical and occupational therapy may be useful, and at the very least can help someone adjust to their newfound disability.

Sources:

Heilman KM (2010): Apraxia. Continuum: Lifelong Learning in Neurology. 16:86-98.

Zadikoff C, Lang AE (2005): Apraxia in movement disorders. Brain. 128:1480-1497.

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