Assessment Of Limb Praxis

A systematic evaluation of praxis is critical in order: (a) to identify the presence of apraxia; (b) to classify correctly the nature of praxis deficit according to the errors committed by the patient and through the modality by which the errors are elicited; and (c) to gain an insight into the underlying mechanism of the patient's abnormal motor behavior (Table 1).

Patients' performance should be assessed in both forelimbs if an elementary motor-sensory deficit does not preclude testing the limb contralateral to the damaged hemisphere. Intransitive and transitive movements should be evaluated. The sample of intransitive gestures tested has to include movements performed toward or on the body (salute, crazy) vs away from the body (okay sign, wave goodbye), repetitive (beckon, go away) or nonrepetitive (sign of victory), since the dimensions of spatial location relative to the body and repetitiveness contribute to the overall complexity of the task and may be differentially influenced by the disorder. Likewise, several types of transitive movements have to be evaluated since it is not an uncommon finding that apraxic patients perform some but not all movements in a particularly abnormal fashion and/or that individual differences appear in some but not all components of a given movement. Therefore, the dissimilar complexity and features of transitive movements should also be considered in order to analyze and interpret praxic errors accurately. For instance, (a) movements may or may not be repetitive in nature (e.g., hammering vs using a bottle opener to remove the cap); (b) an action may be composed of sequential movements (e.g., to reach for a glass and take it to the lips in drinking); (c) a movement may primarily reflect proximal limb control (transport) such as transporting the wrist when carving a turkey, proximal and distal limb control such as reaching and grasping a glass of water, or primarily distal control as when the patient is asked to manipulate a pair of scissors; and (d) movements may be performed in the peripersonal space (e.g., carving a turkey), in body-centered space (e.g., tooth brushing), or require the integration of both, such as the drinking action (4).

Transitive movements should be assessed under different modalities, including verbal, visual (seeing the tool or the object upon which the tool works), and tactile (using actual tools and/or objects) as well as on imitation, since impairment can be seen under some performance conditions but not others. Nevertheless, the most sensitive test for apraxia is asking patients to pantomime to verbal commands because this test provides the least cues and is almost entirely dependent on stored movement representations. In addition to the specific praxis assessment tasks listed in Table 1, it is important to evaluate other cognitive functions, since they may contribute to understand the neural mechanisms of some praxic deficits. Thus, the evaluation of conceptual tool and object knowledge, such as correct naming, descriptions, or correct associative semantic judgement, may help to discern the specific nature of an object/tool use deficit. Knowledge about body image, body structural description, and the effects of changing viewing angles when matching gestures as well as tests of body rotation are necessary to establish the involvement of the processes coding the dynamic position of the body parts of self and others, that is, the body schema, which may also facilitate the comprehension of the praxic defect (16).

Analysis of a patient's performance is based on both accuracy and error patterns (Table 2). One problem with many investigations of apraxia is that the analysis of gestural performance may be insensitive to subtle apraxic deficits, which may have led to an uncorrected estimation about the frequency and degree of apraxia. Therefore, detailed error analysis is crucial to unveil and to properly classify an apraxic disorder. The patient with IA has difficulty mainly is sequencing actions (e.g., making coffee) and exhibits content errors or semantic parapraxias (e.g., mimicking a hammer use when requested to use a knife). Ideomotor apraxia patients show primarily temporal and spatial errors, which are more evident when they perform transitive than intransitive movements. Errors in LKA represent slowness, coarseness, and fragmentation of finger and hand movements (4,17).

Three-dimensional analysis of different types of movements has provided a better and more accurate method to capture objectively the nature of the praxis errors observed in clinical examination. Patients with IMA, due to focal left-hemisphere lesions (18,19), different asymmetric cortical degenerative syndromes (20,21), CBD, PSP, and PD (21,22), have shown several kinematic abnormalities of dissimilar severity, such as slow and hesitant build-up of hand velocity, irregular and non-sinusoidal velocity profiles, abnormal amplitudes, alterations in the plane of motion and in the direction and shapes of wrist trajectories, decoupling of hand speed and trajectory curvature, and loss of interjoint coordination. All these studies have evaluated gestures, such as carving a turkey or slicing a loaf of bread, which mainly explore the transport or reaching phase of the movement. However, the majority of transitive gestures included in most apraxia batteries include prehension (reaching and grasping) movements that reflect proximal (transport) as well as distal limb control (grasping). The kinematic analysis of aiming movements in apraxic patients has demonstrated spatial deficits, in particular when visual feedback is unavailable (23), whereas the analysis of prehension movements in CBD has shown disruption of both the transport and grasp phases of the movements as well as transport-grasping uncoupling (21,24). Furthermore, the study of manipulating finger movements in patients with CBD and LKA has disclosed several abnormalities, which more fully unveil the nature of the deficit. The workspace is highly irregular and of variable amplitude, there is breakdown of the temporal profiles of the scanning movements, and overall, a severe interfinger uncoordination is found (25). Thus, exploration into the kinematics of reaching, grasping, and manipulating may provide useful information regarding the specific neural subsystems involved in patients with different types of limb praxic disorders.

Most of the errors exhibited by IMA cases are equally seen in left- or right-hemisphere-damaged patients when they pantomime nonrepresentative and representative/intransitive gestures, but are observed predominantly in left-hemisphere-damaged patients when they pantomime transitive movements, because it is this action type that is performed outside the natural context (25). The left hemisphere would not only be dominant for the "abstract" performance (i.e., pantomiming to verbal command) of transitive movements but also for learning and reproducing novel movements such as meaningless actions and sequences (27), as well as for action selection (28) and motor attention (29).

Table 2

Types of Praxis Errors

sequencing: some pantomimes require multiple positionings that are performed in a characteristic sequence. Sequencing errors involve any perturbation of this sequence including addition, dele tion, or transposition of movement elements as long as the overall movement structure remains recognizable.

timing: this error reflects any alterations from the typical timing or speed of a pantomime and may include abnormally increased, decreased, or irregular rate of production or searching or groping behavior.

occurrence: pantomimes may involve either single (i.e., unlocking a door with a key) or repetitive (i.e., screwing in a screw with a screwdriver) movement cycles. This error type reflects any mul tiplication of single cycles or reduction of a repetitive cycle to a single event.

amplitude: any amplification, reduction, or irregularity of the characteristic amplitude of a target pantomime.

IC = internal configuration: when pantomiming, the fingers and hand must be in specific spatial rela tion to one another to reflect recognition and respect for the imagined tool. This error type reflects any abnormality of the required finger/hand posture and its relationship to the target tool. For example, when asked to pretend to brush teeth, the subject's hand may close tightly into a fist with no space allowed for the imagined toothbrush handle.

BPO = body-part-as-object: the subject uses his or her finger, hand, or arm as the imagined tool of the pantomime. For example, when asked to smoke a cigarette, the subject might puff on his or her index finger.

ECO = external configuration orientation: when pantomiming, the fingers/hand/arm and the imagined tool must be in a specific relationship to the "object" receiving the action. Errors of this type involve difficulties orienting to the "object" or in placing the "object" in space. For example, the subject might pantomime brushing teeth by holding his hand next to his mouth without reflecting the distance necessary to accommodate an imagined toothbrush. Another example would be when asked to hammer a nail, the subject might hammer in differing locations in space reflecting diffi culty in placing the imagined nail in a stable orientation or in a proper plane of motion (abnormal planar orientation of the movement).

M = movement: when acting on an object with a tool, a movement characteristic of the action and necessary to accomplish the goal is required. Any disturbance of the characteristic movement reflects a movement error. For example, a subject, when asked to pantomime using a screwdriver, may orient the imagined screwdriver correctly to the imagined screw but instead of stabilizing the shoulder and wrist and twisting at the elbow, the subject stabilizes the elbow and twists at the wrist or shoulder.

III.Content P =

perseverative: the subject produces a response that includes all or part of a previously produced pantomime.

related: the pantomime is an accurately produced pantomime associated in content with the target. For example, the subject might pantomime playing a trombone for a target of a bugle. nonrelated: the pantomime is an accurately produced pantomime not associated in content with the target. For example, the subject might pantomime playing a trombone for a target of shaving. the patient performs the action without benefit of a real or imagined tool. For example, when asked to cut a piece of paper with scissors, he or she pretends to rip the paper.

concretization. The patient performs a transitive pantomime not on an imagined object but instead on a real object not normally used in the task. For example, when asked to pantomime sawing wood, the patient pantomimes sawing on his or her leg. no response.

unrecognizable response: the response shares no temporal or spatial features of the target.

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