Apraxia

Apraxia (praxis: Greek for an act, work, or deed) is a neurological disorder characterized by loss of the ability to execute or carry out learned purposeful movements, despite having the desire to and the physical ability to perform the movements.

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Overview

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. It is assumed that when performing an action, the motor engram or “space-time plan' has to be conveyed from the left parietal lobe via association fibers to the 'Central region” according to Liepmann (1920), this includes the pre-central and post-central gyri, the middle and superior frontal gyri and their underlying white matter tracts. The Central region affects action through the primary motor cortex. Many studies have confirmed that the left hemisphere has dominance in praxis (Basso et al., 1980, De Renzi et al., 1980,1982). As apraxia is tested through the use of various pantomimes, it has been found in about 50% of the patients with left hemisphere damage and only less than 10% with right hemisphere damage. Apraxia can also be found in diseases of the basal ganglia, including Parkinson's disease, progressive supranuclear palsy and Huntington’s disease and in isolated lesions of the basal ganglia.

Types

There are several types of apraxia including:

• Speech
• Limb-Kinetic
• Ideomotor
• Ideational
• Eyelid Opening
• Apraxia of Gait
• Constructional
• Oculomotor
• Buccofacial

Apraxia of speech

This term has been introduced first by Lipermann as the general term of ‘apraxia’. It is a condition in which the patient has a motor speech disorder characterized by an impaired ability to coordinate the sequential, articulatory movements necessary to generate speech sounds. It is distinct from other speech and language deficits such as dysarthria, aphasia or stuttering.

There are two types of Apraxia of Speech: Acquired and Developmental apraxia of speech. Acquired apraxia of speech can affect a person at any age. It can be caused due to injuries to the parts of the brain involved with speech and involves the loss of the existing speech ability. This disorder can also result from a stroke, head injury, tumor, or other illnesses that affect brain. Developmental apraxia occurs in children and it is present from birth. This type of apraxia of speech affects more boys than girls. The cause of developmental apraxia is not known yet.

Limb-kinetic apraxia

Limb-kinetic apraxia also called motor apraxia is loss of hand and finger dexterity resulting from inability to connect. It comprises ranges of higher-order motor disorders that result from acquired brain disease affecting the performance of skilled or learned movements with the forelimbs, with or without preservation of the ability to perform the same movement outside the clinical settings in the appropriate situation or environment [1]. Currently, limb apraxia is primarily classified by the nature of the errors made by the patient and the pathways through which these errors are elicited, based on a two-system model for the organization of action: a conceptual system and a production system. Dysfunction of the former would cause ideational (or conceptual) apraxia, whereas impairment of the latter would induce ideomotor and limb-kinetic apraxia [1].

Ideomotor Apraxia

It is a neurological disorder of imitation of gesture, which is common after left hemisphere is damaged, especially when there is involvement of parietal lobe. The patients of this apraxia will have postural inaccuracies such as the wrong location or orientation of hand when attempting to imitate someone placing the palm of their hand under the chin. They cannot perform goal-directed movement. They know what to do but do not know how to do it. They suffer from disturbance of timing, sequencing and spatial organization of gestural movement and these patients make errors when asked to pantomime limb movements involving tools. Testing for ideomotor apraxia can be performed at the bedside with simple tests for the ability to use tools. One of the tests was devised by De Renzi et al. This test uses 24-item imitation with equal meaningful and meaningless movements. Some of these tests involve holding postural gesture while others require the patient to carry out some motor sequence. Score was assigned to correct or not correct attempt. This score is used to determine whether the performance of the patient is pathological.

Ideational Apraxia

This condition is also known as conceptual apraxia in which the patients do not know what to do. Ideational Apraxia is the inability to plan and discriminate between gestures . The ideational praxic patients have the inability to initiate gestures appropriate for the utilization of most objects. Although these subjects are able to comprehend and identify most objects and their use, when asked to imitate use of these objects or to actually use these objects, they exercise this request incorrectly. The disorder can be explained as a disturbance in the concept involved with the organization of action. Patients with ideational apraxia would most likely perform poorly when asked to distinguish correct vs. incorrect gesture use in photographs. Their disability is most evident when the patient must design the action and would be very invisible when a model is provided for them based on verbal instruction (Faglioni & Basso, 1985, Mackay, 1985). Imitation and mimicking movements are also easy for these patients simply because they may use tactile cues, visual information and reference points (Motomura & Yamadori, 1994). As the desired action becomes more difficult by addition steps in a sequence of movements, the disorder becomes more severe (Hecean & Albert, 1978).

The disabilities proposed in ideational apraxia are best reflected in a sequence of motions rather than a single one or two step action of object bound movement (Platz, & Mauritz, 1995). These patients' errors are sequential in nature. Errors shown by these patients have a wide range of variability. For instance, these individuals may stop after the first partial act has been committed (Hecean & Albert, 1978). They may confound the order of the steps by omitting one or several intermediate steps (Hecean & Albert, 1978). A similar action may often be substituted for a desired action (Hecean & Albert, 1978). And lastly, a part of the required action may be omitted or executed using an incorrect object (Poeck, 1985) In all cases, hesitation to a movement is frequent and it is usually repeated during self correction. This indicates the patient is aware of the inadequacy of the motor performance but still performs inappropriately (Poeck, 1985).

Apraxia of Eyelid Opening

Patients suffering from apraxia of eyelid opening are inable to voluntarily open their eyes. The underlying pathophysiology of ALO is not well understood, yet. However, there are some pathological causes proposed by many including inhibition of levator palpebrae (Lepore and Duvoisin, 1985; Fahn, 1988), akinesia of lid opening (Fahn, 1988) and lid freezing (Jankovic et al., 1990). Goldstein and Cogan (1965) described the difficulty in initiating the act of lid elevation in four patients with basal ganglia disease and subsequent reports emphasized the presence of this syndrome in extrapyramidal disorders, in particular PSP (Lepore and Duvoisin, 1985; Krack and Marion, 1994; Boghen, 1997). It is frequently found in association with blepharospasm, and rarely occurs as an isolated entity [2].

Apraxia of Gait

Apraxia of gait is different from ‘leg apraxia’, and often the two do not coexist. Leg apraxia can be tested using similar concepts to those that guide assessment of the upper limb. The patient can be asked to pantomime tasks such as kicking a ball or stubbing a cigarette out with a foot. However, leg apraxia has not been routinely well studied in the examination of praxis, and most of the literature on apraxia concentrates exclusively on the upper limb. This is in part because there is no standardized testing of the lower limb and in part because there are fewer movements (especially complex tasks) that can be tested in the lower limb. It is possible to also assume that there is no such thing as apraxia of gait since walking is more ‘hard wired’. Locomotion is not a consciously learned motor act but rather a repetitive motor pattern generated by spinal mechanisms and modified by brainstem structures. Since apraxia affects learned skills it is obvious that apraxia of gait is unacceptable nomenclature.

Constructional apraxia

Constructional apraxia, typically caused by a lesion in the right cerebral hemisphere, is the inability to construct elements in the correct fashion to form a meaningful whole. It affects the person’s ability to draw or copy simple diagrams or to construct simple figures. For example, the patient would be unable to build a structure with blocks or to copy a design.

Oculomotor apraxia

Ocular Motor Apraxia is an uncommon condition that causes children to have difficulty moving their eyes horizontally or from side to side. It is rare degenerative disorders of the nervous system that usually affects the ability of the patients to quickly move their eyes from side to side and often have to turn their head (head jerking) and not just their eyes to track an object, although they may be able to track a slow moving object. Currently, there are two subtypes of oculomotor apraxia that have been described. Ataxia with oculomotor apraxia 1 is caused by a mutation in the APTX gene at locus 9p13.3. The APTX gene encodes for the APTX protein, a ubiquitously expressed histidine triad nuclear protein whose function remains unclear; some researchers have suggested a role in DNA repair[3]. Several different APTX mutations were reported in ataxia with oculomotor apraxia 1: R199H and P206L, which are missense mutations; V230, a frameshift mutation; and W279X, a stop mutation. A later study described an additional four mutations, namely A198V, D267G, W279R, and IVS5+1. [11] There is some genotype-phenotype correlation with later onset of the ataxia in patients with the missense mutation. The Japanese patients with mental retardation were all compound heterozygous for 689-690Ins T/P206L. [8, 9] Children suspected of having ocular motor apraxia should be evaluated by a Pediatric Neurologist and a Pediatric Ophthalmologist. Therapy through an early childhood intervention program for occupational and/or physical therapy may also be helpful.

Buccofacial apraxia

Buccofacial apraxia patients cannot perform skilled movements involving the lips, mouth, and tongue in the absence of paresis. Sometimes called facial-oral apraxia, it is the inability to coordinate and carry out facial and lip movements such as whistling, winking, coughing, etc, on command. This form includes verbal or speech developmental apraxia, perhaps the most common form of the disorder. Although it is probably the most frequent types of all apraxia due to focal brain lesions, buccofacial apraxia seldom assessed in clinical practice and very few controlled experimental studies have been carried out [2]. This buccofacial apraxia has, with rare exceptions, been associated with left hemispheric lesions in right-handers.

Causes

Different apraxias have various causes. However, animal and human studies, using both electrophysiology and functional imaging, have tried to define the role of the basal ganglia in producing apraxia.

Apraxia of speech can be caused from vascular lesion or tumors and trauma. AOS is associated with structural damage or low blood flow in the left posterior frontal gyrus. Study also shown that in AOS patients there is focal atrophy in frontal operculum, premotor and primary motor cortices as well as the inferior frontal gyrus, left insula and subcortical regions.

In the case of ideomotor Apraxia, patients have normal dexterity, and the error is not due to problems involving any limb weakness akinesia, differentiation, abnormal tone or posture, dementia, poor comprehension. There are some anatomical diverse lesions mainly in left hemisphere; typically involve parietal association areas and white matter bundles connecting frontal and parietal association areas. There is less commonly premotor and supplementary motor cortex involvement as well as basal ganglion and thalamus.

Treatment

There is no one treatment proven to be effective for all the patients suffering from AOS. Some therapies focus on improving communication effectiveness. For the mild AOS, patients can be treated by working on their primary speech deficit and, therefore, the goal is to improve intonation and stress. They can also be treated by teaching them oral postures for individual speech sounds. Some of the techniques employed includes: traditional articulate therapy (repetitive exercises involving imitation of speech sounds and words) ( Rosenbeck, et al., 1973), finger tapping or pacing (Dworkin et al., 1988), singing and EMG feedback to reduce tension (McNeil et al., 1976; Wambaugh, 2002).

Prognosis

The prognosis for individuals with apraxia varies. With therapy, some patients improve significantly, while others may show very little improvement. Some individuals with apraxia may benefit from the use of a communication aid. The potential for significant improvements with treatments and self-healing (spontaneous recovery) are also most likely in cases of mild apraxia with stable medical courses. For more severe cases, particularly those with progressive or unstable neurological pathologies, the prognoses for no-table gains with medical and behavioral interventions remain guarded at the outset. However, many such cases achieve sufficient gains to enable independent lifestyles.

Links

• http://www.apraxiadallas.com
• http://www.apraxia-kids.org

References

Primary Source

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• Bruno Laeng, “Constructional apraxia after left or right unilateral stroke.” Neuropsychologia 44 (2006) 1595–1606
• C. Rosci, V. Chiesa, M. Laiacona and E. Capitani ,“Apraxia is not associated to a disproportionate naming impairment for manipulable objects,” Brain and Cognition, Volume 53, Issue 2, November 2003, Pages 412-415.
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