Embed Size (px)
Citation preview
592 nature clinical practice neurology november 2008 vol 4 no 11
www.nature.com/clinicalpractice/neuro
commentary
During the past decade, the approach to stroke therapeutics has evolved from ‘diagnose and adios’ to immediate and aggressive intervention. Intravenous tissue plasminogen activator administered within 3 h of symptom onset is now the standard of care for acute ischemic stroke, and several pharmacologic and endovascular approaches to the treatment of acute stroke are being advanced.1 With the development and routine use of multimodal CT and MRI, imaging findings have become important variables to consider when formulating individualized treatment plans.2 When choosing a therapy, clinicians must determine, amongst other things, whether there is an occlusion in one of the major arteries supplying blood to the brain or if there is evidence of permanent parenchymal injury. As long as sensitive tests are performed, evidence of either feature should prompt an aggressive course of action, and negative findings a more conservative one. A proximal occlusion suggests that a large area of tissue is at risk and is associated with poor functional outcome; therefore, identifying such a lesion can help clinicians to predict a patient’s outcome.3 In this regard, a new classification instrument for predicting outcome after stroke, the Boston Acute Stroke Imaging Scale (BASIS), has the potential to become a useful tool for clinical care and research.4 BASIS incorporates
SummaryThis Practice Point commentary discusses a report by Torres-Mozqueda et al. on a newly developed classification instrument for predicting outcome after stroke, the Boston Acute Stroke Imaging Scale (BASIS). This tool incorporates imaging data on the patency of the vasculature and the parenchyma and classifies ischemic strokes as major (if large vessels are occluded or parenchymal changes are present) or minor (all others). When testing the scale, the authors looked at short-term outcome at the time of hospital discharge; patients classified with major stroke by BASIS had a higher mortality and longer hospital stay and were more likely to be discharged to a rehabilitation facility than patients with minor stroke. The authors concluded that BASIS can predict outcome after stroke. We point to several shortcomings in the study methodology and argue that, although BASIS has potential as a prognostic tool, further studies are needed before it can be widely used.
keywords acute stroke, imaging, MrI, prognosis
data on the patency of the vasculature and the presence of early parenchymal changes; ischemic stroke is classified as major if there is a large vessel occlusion on CT angiography or magnetic resonance angiography or noteworthy parenchymal abnormality on CT or MRI, and as minor if both these features are absent.
To determine whether BASIS accurately predicts outcome after stroke, TorresMozqueda and colleagues used this tool to classify 230 patients who had a discharge diagnosis of ischemic stroke.4 The majority (n = 205) of these individuals had CT angiography or magnetic resonance angiography, performed soon after the onset of symptoms, as part of their imaging protocol. A further 25 patients who underwent CT or MRI only were also included in the study. Outcomes at the time of hospital discharge were evaluated. In accordance with BASIS, 59 patients were classified with major stroke, and 171 patients were classified with minor stroke. There were 8 deaths (3.5% of patients), all of which occurred in the major stroke group. Not surprisingly, survivors with a major stroke stayed longer in the hospital (mean 12.5 days vs 3.2 days), were more likely to be discharged to a rehabilitation facility (72% vs 17%), and were less likely to be discharged home (18% vs 76%) than patients with a minor stroke.
Several methodological issues constrain both the interpretation and the implication of these
JG Merino is Medical Director of the Suburban Hospital Stroke Program, and LL Latour is a Staff Scientist in the Section on Stroke Diagnostics and Therapeutics at the National Institute of Neurological Disorders and Stroke, Bethesda, MD, USA.
Correspondence*Suburban Hospital Stroke Program 8600 Old Georgetown Road Bethesda MD 20814 USA [email protected]
received 6 April 2008 accepted 19 August 2008 Published online 30 September 2008
www.nature.com/clinicalpracticedoi:10.1038/ncpneuro0919
The Boston Acute Stroke Imaging Scale: ready for use in clinical practice? José G Merino* and Lawrence L Latour
practice point practice pointpractice point
november 2008 vol 4 no 11 nature clinical practice neurology 593
www.nature.com/clinicalpractice/neuro
Competing interestsThe authors declared no competing interests.
results. The most important concern is the choice and timing of the outcome measures. Measuring outcome at the time of hospital discharge is problematic, because recovery may continue over months, and the degree and timing of recovery relate to the initial severity of the stroke. For this reason, clinical trials usually evaluate outcome several months after stroke.5 Additionally, other than death, the outcome measures in the study do not reflect longterm functional status. The length of hospital stay is affected by comorbidities and administrative factors, and discharge to a rehabilitation facility is not necessarily a bad outcome and does not reflect longterm functional status. Other methodological shortcomings of the study include possible biases regarding the selection of imaging modality and timing of image acquisition, and the failure to take into account in the analysis the effect of important clinical variables (e.g. age and stroke severity) that most studies show are powerful significant independent predictors of outcome.6 In addition, patients imaged with CT were more likely to be classified with major stroke than patients imaged with MRI (49% vs 11%), and, regardless of modality, patients with major stroke had a shorter time from symptom onset to imaging than did patients with minor stroke. Furthermore, the study did not include patients without stroke, so the sensitivity and specificity of the scale cannot be determined.
Imaging has led to a greater understanding of stroke pathophysiology, and imaging markers may eventually be routinely used to match patients with potential therapies. New imaging techniques and classification instruments such as BASIS may ultimately improve patient care, but they must be validated in randomized trials before they can be used in routine clinical practice and in research studies. Progress has been made in this respect. Several ongoing or recently completed clinical trials of thrombolytic agents used up to 24 h after symptom onset
have relied on imaging for patient selection in an attempt to replace the time window with a tissue window,7 and at least one study, the MR and Recanalization of Stroke Clots Using Embolectomy (MR Rescue) trial, tests the primary hypothesis that the penumbral pattern can predict the patients most likely to respond to treatment. Incorporating objective evidence of pathology through the use of imaging to confirm and grade the severity of an ischemic insult is a step in the right direction; it will help clinicians to identify which patients are suitable for different therapies, as well as those who will have a bad outcome regardless of treatment. An instrument such as BASIS could ultimately become an important tool for achieving these goals.
references1 Sacco RL et al. (2007) Experimental treatments for
acute ischaemic stroke. Lancet 369: 331–341 2 Hjort N et al. (2005) Magnetic resonance imaging
criteria for thrombolysis in acute cerebral infarct. Stroke 36: 388–397
3 Schellinger PD et al. (2001) Stroke magnetic resonance imaging within 6 hours after onset of hyperacute cerebral ischemia. Ann Neurol 49: 460–469
4 Torres-Mozqueda F et al. (2008) An acute ischemic stroke classification instrument that includes CT or MR angiography: the Boston Acute Stroke Imaging Scale. AJNR Am J Neuroradiol 29: 1111–1117
5 Duncan PW et al. (2000) Outcome measures in acute stroke trials: a systematic review and some recommendations to improve practice. Stroke 31: 1429–1438
6 König IR et al. (2008) Predicting long-term outcome after acute ischemic stroke: a simple index works in patients from controlled clinical trials. Stroke 39: 1821–1826
7 Köhrmann M and Schellinger PD (2007) Stroke-MRI: extending the time-window: recent trials and clinical practice. Int J Stroke 2: 53–54
PractIce PoIntThe Boston Acute Stroke Imaging Scale (BASIS) takes into account imaging findings of the patency of the vasculature and the presence of early ischemic changes in the parenchyma and is, therefore, potentially useful in predicting outcome after stroke. However, this scale must be evaluated with robust methodology before its use in routine clinical practice or in research studies can be advocated.
practice point practice pointpractice point
