Face apraxia refers to a disturbance of upper and lower face movements not explained by elementary motor or sensory deficits. Patients exhibit spatial and temporal errors of similar quality to those observed in the limbs when performing representational and nonrepresentational movements such as sticking out the tongue, blowing out a match, smiling, blowing a kiss, showing the teeth, blinking the left or right eye, looking down, or sucking on a straw. Although lower face or buccofacial apraxia often coexists with Broca's aphasia, and thus is more frequently observed with left-hemisphere lesions, in particular involving the frontal and central operculum, insula, centrum semiovale, and basal ganglia (51), it can also be seen with lesions confined to left posterior cortical regions as well as with right-hemisphere damage (52).
Apraxia of eyelid opening has been defined as a nonparalytic inability to open the eyes at will, in the absence of visible contraction of the orbicularis oculi muscle owing to involuntary palpebral levator inhibition (53). Many patients show a forceful contraction of the frontalis muscle and/or a backward thrusting of the head on attempting eyelid opening and use different types of maneuvers to help open the eyes including opening the mouth, massaging the lids, and manual elevation of the lids. However, apraxia of eyelid opening can hardly be considered a "true" apraxia but rather a subclinical form of blepharospasm because (a) most patients exhibit abnormal persistence of orbicularis oculi activity detected at electromyography; (b) it is commonly associated with overt blepharospasm; and (c) it is particularly observed in patients with basal ganglion disorders (54).
Truncal or whole body apraxia is a disorder of axial movements neither attributable to elementary motor (e.g., extrapyramidal) or sensory deficit nor to dementia. Patients have difficulties dancing or turning around and may be unable to adapt the body to the furniture; patients have difficulty sitting down in a chair, showing hesitation, sitting in a wrong position (e.g., on the edge of the chair) and in incorrect directions (e.g., facing the back of the chair). When lying in bed, their body is not aligned parallel to the major axis of the bed and they place the pillow in an unusual position. Patients may have minimal or no difficulty in standing or getting up, in contrast to features of some basal ganglion disorders such as parkinsonism. Truncal apraxia is seen with bilateral hemispheric damage involving the parietal or parieto-temporal cortex or affecting parietofrontal connections (55,56).
THE NATURE OF APRAXIA IN ATYPICAL PARKINSONISMS Corticobasal Degeneration
Limb apraxia is a prominent clinical feature and the most widely studied cognitive deficit in CBD. It is almost invariably asymmetric and more frequent in patients whose initial symptoms were in the right limb (left-hemisphere dominance) than in the left limb (right-hemisphere dominance), in agree ment with the fact that most right-handers develop IMA as well as IA predominantly with left-hemisphere lesions (10,21). In CBD, IMA is the most common type of limb praxic deficit. Patients exhibit temporal and spatial errors more frequently when performing transitive than intransitive movements. Spatial errors such as incorrect positioning of the hand to grasp the tool (internal configuration errors), difficulty in orienting the hand with respect to the body and the tool with respect to the object receiving the tool's action in extrapersonal space (external configuration errors), abnormal movement trajectories, and timing errors were those more frequently found whereas body-part-as-object and sequencing errors were not so common (videotapes 1 and 2). All these patients have difficulties when imitating meaningful and meaningless postures and movements and some exhibited even more errors when imitating than pantomiming gestures to command. Thus, there is no consistent pattern when comparing performance on gestures to command with imitation and the use of the real object/tool, since some patients may have more difficulties when imitating than pantomiming gestures and occasional patients perform worse when handling the objects than pantomiming to command or the reverse, show a dramatic improvement when holding the tool/object (10,21,57-63).
CBD patients may not only exhibit spatiotemporal errors when handling objects but in addition may often show impairment in the selection and usage of novel tools in the mechanical problemsolving task (63); on occasion, they may also commit content errors and perform wrongly the sequential arm movement test, displaying errors such as omissions, misuse, mislocations, and intrusions, as well as pantomime recognition deficits (10). Therefore, a consistent production or executive deficit may frequently combine with mechanical problem-solving impairment and less commonly with semantic knowledge breakdown as well (63). However, disruption of conceptual knowledge and IA (content errors or semantic parapraxias) are uncommon in CBD patients; this type of praxic deficit is particularly observed in patients with cognitive impairment including aphasia and dementia (10,64), or in the presence of primitive reflexes (10). The combination of several types of limb praxic deficits relevant for object use clearly explains why CBD patients are far more disabled in everyday life than any patients with other atypical parkinsonian diseases.
The limb-kinetic type of apraxia has also been frequently reported in CBD (21,25,49,50,65). Patients show slow, awkward, and mutilated finger and hand movements; on occasion, movements are amorphous and contaminated by extraneous movements. Difficulties are particularly evident with motor skills requiring fractionated or sequential fingers movements. Imitation of finger postures is abnormal and some patients use the other hand to move the abnormal one to reproduce the requested posture. At times, the fingers and hand remain in an abnormal posture while the patient performs other tasks with the contralateral hand. Perseveration of postures and movements is commonly observed. Patients are aware of the poor performance but are unable to correct their errors (21) (video 3, see companion DVD). Kinematic studies in these patients showed severe disruption of manipulative movements with marked interfinger uncoordination (25).
The prevalence of facial (buccofacial) apraxia in CBD is unclear. Pillon et al. (58) found orofacial apraxia in their patients though milder than limb apraxia. We only demonstrated orofacial apraxia in 4 out of 16 patients (21) but other authors failed to mention it in their studies (57,59). However, in a recent study by Ozsancak et al., orofacial apraxia, as evaluated by means of simple and sequential gestures, was found in 9 of 10 patients with a clinical diagnosis of CBD (66). Lastly, truncal apraxia has also been recorded in CBD patients (56).
The brunt of the pathology in CBD is located in the superior frontal gyrus, which is more often affected than the middle and inferior gyri, the pre- and postcentral regions, the anterior corpus callo-sum, the caudate, putamen, globus pallidus, thalamus, and substantia nigra, with atypical asymmetric distribution (67). Functional brain-imaging studies have disclosed decreased metabolism in the frontoparietal region, particularly in the superior prefrontal cortex, lateral and mesial premotor areas, in the sensorimotor and parietal association cortices, as well as in the caudate, lenticular, and thalamic regions with striking interhemispheric asymmetries, the hemisphere contralateral to the more affected limb proving more severely involved (68).
The particular distribution of the pathological process in patients with CBD clearly explains the disruption of the cortical and subcortical components of the multiple, parallel, sensorimotor transformation circuits, and hence the severe IMA observed in these patients. An action selection deficit owing to involvement of parietal and premotor cortices and basal ganglia on the left hemisphere may further aggravate the praxic disorder. Moreover, frequent breakdown in mechanical problem solving as a result of parietal lobe pathology and the occasionally observed impairment in object-specific conceptual knowledge, probably related to temporofrontal pathology, explain the IA disorder and the rarely observed gesture recognition deficit (10). The limb-kinetic type of praxic deficit is mainly related to damage to the circuits subserving grasping and manipulation; in addition, it may be further aggravated by derangement of independent finger movements and by dysfunction of somatosensory control of manipulation (25). Involvement of inhibitory areas in the inferior and superior frontal gyri and damage to subcortical structures may reduce facilitation of inhibitory interneurones, causing defective cortical inhibition, which in turn may also interfere with the selection and control of finger muscle activity. We found reduced cortical inhibition, as reflected by a short silent period, in CBD patients with LKA (25). Finally, an associated sensory defect because of parietal damage may interfere with the kinaesthetic and tactile information necessary for somatosensory control of manipulation; however, as a defect in somaesthesis may not be present and parietal involvement may be absent in patients with CBD, LKA may basically result from bilateral dysfunction of nonprimary cortical motor areas (25).
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