Published online before print September 18, 2003, doi: 10.1161/01.STR.0000094661.43891.F9
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(Stroke. 2003;34:2396.)
© 2003 American Heart Association, Inc.
Original Contributions |
Editorial Comment—Measurement of Cognitive Deficits in Acute Stroke
Department of Neurology, University of Florida College of Medicine, Jacksonville, Florida
Department of Neurology, University of Florida College of Medicine, Veterans Affairs Medical Center, Gainesville, Florida
Whereas diffusion-weighted imaging (DWI) identifies areas of metabolic failure and cellular injury that are often, but not invariably, irreversible,1 perfusion-weighted imaging (PWI) depicts areas of hypoperfusion that, when not matched by a diffusion abnormality, constitute the potentially reversible ischemic penumbra.2 Early neurological deficits correlate with core and penumbral lesion volume rather than with the diffusion abnormality.3 These new imaging techniques are powerful tools that provide insights into the pathophysiology of the deficits and the effects of therapeutic interventions in patients with acute stroke.
Earlier SPECT observations showed that patients with subcortical stroke and aphasia or neglect had decreased cortical perfusion that was attributed to the interruption of neural connections (diaschisis).4 Using neuropsychological tests and PWI, however, Hillis and colleagues have shown that patients with subcortical strokes have aphasia and neglect because of the cortical hypoperfusion,5 and that these deficits improve when blood flow to the cortex is restored.5,6 In this issue of Stroke, Hillis et al demonstrate that a battery of neurobehavioral tests that assess language and attention correlates well with the volume of hypoperfused cortex but that the National Institute of Health Stroke Scale (NIHSS) score correlates poorly when the left hemisphere is involved and not at all when right hemisphere is injured. Neither neurobehavioral nor NIHSS scores correlated with DWI abnormalities, regardless of which hemisphere was affected.7 Furthermore, in a second experiment, they found that among patients with right-sided stroke, treatment-induced changes in perfusion correlate with changes in performance on the line cancellation task but not with changes in the NIHSS score.7
Attention depends on a complex neuroanatomically distributed modular network8 that includes the dorsolateral prefrontal lobes, the posterior and superior temporal and inferior parietal lobes, the cingulate gyrus, and portions of the diencephalic and mesencephalic reticular activating system. Lesions anywhere in this network, particularly—but not exclusively—in the right hemisphere, can lead to attention abnormalities including extinction, hemispatial neglect, personal neglect, and anosognosia. Attention deficits are found in 20% to 40% of patients 3 months after a stroke.9,10 While these deficits do not always precisely localize the lesion, it is important to identify them because they are disabling and negatively impact rehabilitation. They are, however, rarely elicited or recorded by neurologists in the acute stage, particularly when a standardized scale is not used.11
The findings reported in this issue by Hillis and colleagues highlight some issues regarding the NIHSS that have been previously identified.12,13 This scale is used to select acute stroke patients for treatment with pharmacological and mechanical agents, and is a measure of stroke severity in many prospective stroke databases. The scale, however, is biased toward left hemisphere strokes, since 7 out of 42 possible points are assigned to language dysfunction while only 2 are given for neglect. As a result, for a given NIHSS score the volume of acute diffusion-weighted (DWI) abnormality13 and of infarction on CT12 is larger when the stroke is in the right, particularly if the deficits are mild.13 This bias has significant implications. Patients with low NIHSS scores are seldom treated with tissue plasminogen activator, even though one third of the untreated patients die or are dependent at discharge.14 In addition, higher NIHSS score and stroke volume are associated with worse outcomes,15,16 and when strokes of similar size in both hemispheres are compared, those in the right lead to worse outcomes.17
Hillis et al demonstrate that a battery of cognitive tests that takes about 45 minutes to administer correlates with PWI abnormalities.5–7 We need a shorter instrument for use in clinical care and research in the acute setting. Hillis et al chose the line cancellation task for the second experiment for its sensitivity and reliability. However, different tests assess separate components of the neglect syndrome, and patients may perform well on one test but not on the other.18 Binder and colleagues did not find a correlation between the scores in the line bisection and the letter cancellation tasks.19 Perhaps a measure that combines elements of both tests, such as one recently proposed by Na and coworkers, will be useful.20 This test consists of horizontally aligned strings of characters and the subject’s task is to mark a target character that is at, or closest to, the true midpoint of the simulated line. The sensitivity and specificity of this task in the setting of acute stroke, however, still need to be established.
More than 60% of patients have deficits in at least one cognitive domain 3 months after a stroke,10 yet cognitive disorders are often either overlooked or underestimated in the assessment of acute stroke. Clinical trials inadequately assess cognitive status as an outcome measure. In their second experiment, Hillis and colleagues demonstrate the value of using cognitive outcomes—the treatment associated change in perfusion correlated with changes in performance of line cancellation task but not with changes in the NIHSS.7 Thus, there is a need for a cognitive scale that can be used in conjunction with the NIHSS both to select patients for acute stroke treatment and to be used as baseline and outcome measure in clinical trials. Such a scale must allow prompt evaluation of the domains that are most often affected by stroke and must be simple to administer by physicians who are not familiar with neurobehavioral testing. Like the NIHSS it should provide an overall numeric score, but should also provide subscores that can be used to track changes in individual domains over time. The scale can have a brief multicognitive domain screening section that can be applied in a few minutes before treatment, and more detailed components to address domains where the patient performed abnormally. Data such as those presented by Hillis et al in this issue should be the basis for such a scale.
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