Abnormalities of praxis are assessed by clinical history and the bedside neurological examination. Complementary investigations, such as neuroimaging, electrophysiology, fluid and tissue analysis, and neuropsychological testing can contribute to the etiological diagnosis.
Neuroimaging. Neuroimaging can be very useful in localizing and identifying the various disorders that present with praxis abnormalities. While the clinical history and examination are most helpful in distinguishing apraxia due to an acute process, such as stroke, from a more chronic process such as the degenerative disorders, magnetic resonance imaging (MRI) and computed tomography (CT) are useful in differentiating the causes of stroke (hemorrhage, ischemia) and in ruling out central nervous system malignancies. Additionally, these imaging studies (particularly MRI) may show the areas of cortical atrophy in patients with degenerative disorders. Unilateral, predominantly parietal, atrophy suggests corticobasal ganglionic degeneration, whereas bilateral temporoparietal atrophy is associated with Alzheimer's disease. Single-photon emission computed tomography (SPECT) may be useful in demonstrating
decreased cortical activity when obvious atrophy is not observed. Photon-emission tomography (PET), utilizing oxygen metabolism and 18F-dopa uptake, can demonstrate asymmetrical hypometabolism in the posterior frontal, inferior parietal, and lateral temporal cortex, striatum, and thalamus in patients with corticobasal ganglionic degeneration, whereas patients with Alzheimer's disease generally show hypometabolism of the parietotemporal and frontal association area, which may be asymmetrical or symmetrical, but striatal metabolism is preserved.
Electrophysiology. Electroencephalography is one measure of cortical function, and the finding of asymmetrical or symmetrical slowing may aid in the localization of pathology in patients with apraxia. Electromyography and nerve conduction studies are generally of little use in the evaluation of patients with apraxia.
Cerebrospinal Fluid and Tissue Analysis. Cerebrospinal fluid (CSF) analysis is generally not helpful in differentiating the causes of apraxia, demonstrating at most nonspecific findings in patients with stroke or degenerative disorders. Brain biopsy, while potentially diagnostic in patients with apraxia associated with Alzheimer's disease or corticobasal ganglionic degeneration, is indicated only in atypical cases or when the history and examination suggest other potentially treatable etiologies.
Neuropsychological Tests. In addition to bedside testing of praxis function, additional neuropsychological tests may be useful in differentiating early degenerative disorders such as Alzheimer's disease, corticobasal ganglionic degeneration, or Pick's disease (see Chapte.L33 ).
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