Although frequent (13,62), limb apraxia is not a clinical feature included in the diagnostic criteria of PSP (69,70). Bilateral IMA mainly for transitive movements, slightly asymmetric, and almost always more pronounced in the nondominant limb is the most consistent finding. IMA for intransitive movements is usually less frequent and severe. The praxic deficit is particularly evident when patients pantomime under verbal command, improve on imitation and more with the use of the tool/ object (13,58,62). Spatial (i.e., internal and external configuration, trajectory) are more prominent than temporal errors (i.e., hesitation, delay); perseveration and sequencing errors are uncommon; content errors are not found (13) (video 4). PSP patients rarely develop abnormal motor behavior compatible with LKA (13,58). Ideomotor apraxia seems to correlate significantly with cognitive deficits as measured with Mini Mental State Examination (MMSE). Recognition of pantomimes is normal, but on occasion patients may fail on the multiple-step task (13). Facial (orofacial) apraxia may be found, though it may be difficult to interpret the exact nature of the abnormal performance given the unique facial appearance usually present in PSP patients (13). In turn, apraxia of eyelid opening is common and may be very disabling (70).
The ideomotor type of praxic deficit is qualitatively similar in PSP and PD patients, though more frequent and usually more severe in the former (13), as also demonstrated by the use of three-dimensional motor analysis (22).
Limb apraxia is not observed (13), or exceptionally found with MSA (15) and has not been systematically studied in patients with demential Lewy bodies (DLB). However, we have found IMA with predominantly imitative deficits in three patients with mild to moderate DLB as clinically diagnosed by McKeith et al. criteria (72) (see also Abeleyra et al., in preparation) (videotape 5).
Limb apraxic deficits in PSP seem to correlate with low MMSE, whereas in PD they appear to correlate with neuropsychological tests reflecting frontal lobe dysfunction and visuospatial cognitive deficits (13). Since focal lesions restricted to the basal ganglia only rarely cause apraxia and patients with MSA, which is characterized by severe basal ganglion and slight cortical involvement, fail to exhibit praxic deficits, we suggested that apraxia in PSP and PD reflect combined corticostriatal dysfunction (13). Cortical degeneration is now recognized to be common in PSP and identified mainly in the cingulate, superior, and medial frontal gyri (72,74). However, in PSP patients with limb apraxia cortical pathology may predominate in motor cortices or coexist with Alzheimer's disease pathology (74).
Comparison of Different Types of Praxic Disorders Among CBD, PSP, MSA, and DLB
Praxic Disorder CBD PSP MSA DLB
Limb Apraxia Ideomotor
Pantomiming to verbal commands Object use Imitation Intransitive gestures Asymmetry
Voluntary / automatic dissociation Mechanical problem solving Ideational
Conceptual errors Sequencing Limb-kinetic
Pantomime recognition / discrimination Facial apraxia Apraxia eyelid opening Truncal apraxia
In PD patients, impairment of neuropsychological tests reflecting frontal lobe function correlated with reduced fluorodopa uptake in caudate nucleus (75), and proton magnetic resonance spectroscopy (MRS) may detect temporoparietal cortical dysfunction in nondemented patients with PD (76). Therefore, it seems plausible that the subgroups of PD patients developing limb apraxia and more severe kinematic abnormalities in the spatial precision of movements and interjoint coordination (22) are those with greater caudate nucleus and frontal lobe involvement with or without temporoparietal cortical dysfunction (36). Thus, basal ganglion pathology per se would not cause overt apraxia. However, when combined with dysfunction of the cortical components of the neural circuits devoted to sensorimotor transformation, sequencing, and action selection, various types of praxic deficits would become clinically manifested (36).
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