Evidence-based guideline: The role of diffusion and perfusion MRI for the diagnosis of acute
Miriam G.Brazzelli, University of Edinburgh, Division of Clinical Neurosciences, University of Edinburgh, Western General Hospital, Edinburgh, UKm.brazzelli@ed.ac.uk
Peter Sandercock (Edinburgh, UK; peter.sandercock@ed.ac.uk), Joanna Wardlaw (Edinburgh, UK; joanna.wardlaw@ed.ac.uk)
Submitted January 19, 2011
Schellinger et al. assessed the evidence on DWI and PWI for the diagnosis of acute ischemic stroke. [1]
While the authors stated that they systematically analyzed the literature to address the diagnostic value of DWI, their selection criteria were not clearly described and they failed to report potentially relevant studies. [6] Schellinger et al. categorized the evidence using a simple, non-validated, four-tier classification based on the type of study design and a few study characteristics but they did not formally appraise the quality of the identified evidence [7] or assess compliance with the recommended standards for reporting of diagnostic studies. [8] Moreover, their classification did not differentiate between single test studies and studies that compared imaging tests directly (i.e., DWI and CT in the same patients versus an acceptable reference standard).
The authors concluded that DWI is superior to CT in patients presenting within 12 hours of symptom onset according to the findings of four studies (one Class I study and 3 Class II studies). However, all of these studies included patients with high probability of stroke and very few stroke mimics, which makes the sample poorly representative of the acute patients typically seen in clinical practice.
Furthermore, the Class I study primarily included mild strokes (median NIHSS=3) and counted TIAs with imaging evidence of cerebral infarction as true positive cases (i.e. as strokes rather than TIAs). This would have inflated the sensitivity of DWI and may suggest that the reference standard was switched to a MRI diagnosis. In the third Class II study where CT and DWI were assessed using the Alberta Stroke Program Early CT Score, the CT estimates were calculated assuming DWI as reference standard.
Considering the limited number and quality of the identified evidence, their conclusions on the accuracy of DWI and CT are perhaps overly optimistic and not entirely justified. We recently published a review of comparative studies on MRI versus CT for the diagnosis of acute stroke. [9] Our results indicate that DWI is probably more sensitive than CT, but not more specific, for the early detection of ischemic stroke in highly selected patients.
Due to the few comparative studies available and their limited methodological quality, we believe that any other conclusion would be misleading.
References
6. Barber PA, Darby DG, Desmond PM, et al. Identification of major ischemic change. Diffusion-weighted imaging versus computed tomography. Stroke 1999;30:2059-2065.
7. Whiting P, Rutjes AW, Reitsma JB, Bossuyt PM, Kleijnen J. The development of QUADAS: a tool for the quality assessment of studies of diagnostic accuracy included in systematic reviews. BMC Medical Research Methodology 2003;3:25.
8. Bossuyt PM, Reitsma JB, Bruns DE et al. Standards for Reporting of Diagnostic accuracy steering group. Towards complete and accurate reporting of studies of diagnostic accuracy: the STARD initiative. BMJ 2003;326:41-44.
9. Brazzelli M, Sandercock PAG, Chappell FM et al. Magnetic resonance imaging versus computed tomography for detection of acute vascular lesions in patients presenting with stroke symptoms. Cochrane Database of Systematic Reviews 2009, Issue 4. Art. No.: CD007424. DOI: 10.1002/14651858.CD007424.pub2.
Disclosures: Dr. Brazzelli reports no disclosures.Dr. Sandercock serves as a member of the Data and Safety Monitoring Board (DSMB), UK for three stroke clinical trials; serves as a Coordinating Editor for the Cochrane Stroke Group, UK; receives research grants from the Medical Research Council, UK (EME 09/800/15) and the National Institute for Health Research (NIHR), UK (EME 08-43-52) for stroke and imaging research. Dr. Wardlaw is Professor of Neuroradiology at the University of Edinburgh, UK; receives research funding from the Scottish Funding Council, UK, the National Institute for Health Research Emerging Medicines Evaluation, UK, and the Scottish Funding Council SPIRIT Scheme, UK; received research support from Wyeth/TMRI Ltd the Row Fogo Trust (AD.ROW4.35, R35865), the UK Stroke Association (TSA 2006/11), the Wellcome Trust, UK (088134/Z/09) for independent academic imaging research.
Schellinger et al. assessed the evidence on DWI and PWI for the diagnosis of acute ischemic stroke. [1]
While the authors stated that they systematically analyzed the literature to address the diagnostic value of DWI, their selection criteria were not clearly described and they failed to report potentially relevant studies. [6] Schellinger et al. categorized the evidence using a simple, non-validated, four-tier classification based on the type of study design and a few study characteristics but they did not formally appraise the quality of the identified evidence [7] or assess compliance with the recommended standards for reporting of diagnostic studies. [8] Moreover, their classification did not differentiate between single test studies and studies that compared imaging tests directly (i.e., DWI and CT in the same patients versus an acceptable reference standard).
The authors concluded that DWI is superior to CT in patients presenting within 12 hours of symptom onset according to the findings of four studies (one Class I study and 3 Class II studies). However, all of these studies included patients with high probability of stroke and very few stroke mimics, which makes the sample poorly representative of the acute patients typically seen in clinical practice.
Furthermore, the Class I study primarily included mild strokes (median NIHSS=3) and counted TIAs with imaging evidence of cerebral infarction as true positive cases (i.e. as strokes rather than TIAs). This would have inflated the sensitivity of DWI and may suggest that the reference standard was switched to a MRI diagnosis. In the third Class II study where CT and DWI were assessed using the Alberta Stroke Program Early CT Score, the CT estimates were calculated assuming DWI as reference standard.
Considering the limited number and quality of the identified evidence, their conclusions on the accuracy of DWI and CT are perhaps overly optimistic and not entirely justified. We recently published a review of comparative studies on MRI versus CT for the diagnosis of acute stroke. [9] Our results indicate that DWI is probably more sensitive than CT, but not more specific, for the early detection of ischemic stroke in highly selected patients.
Due to the few comparative studies available and their limited methodological quality, we believe that any other conclusion would be misleading.
References
6. Barber PA, Darby DG, Desmond PM, et al. Identification of major ischemic change. Diffusion-weighted imaging versus computed tomography. Stroke 1999;30:2059-2065.
7. Whiting P, Rutjes AW, Reitsma JB, Bossuyt PM, Kleijnen J. The development of QUADAS: a tool for the quality assessment of studies of diagnostic accuracy included in systematic reviews. BMC Medical Research Methodology 2003;3:25.
8. Bossuyt PM, Reitsma JB, Bruns DE et al. Standards for Reporting of Diagnostic accuracy steering group. Towards complete and accurate reporting of studies of diagnostic accuracy: the STARD initiative. BMJ 2003;326:41-44.
9. Brazzelli M, Sandercock PAG, Chappell FM et al. Magnetic resonance imaging versus computed tomography for detection of acute vascular lesions in patients presenting with stroke symptoms. Cochrane Database of Systematic Reviews 2009, Issue 4. Art. No.: CD007424. DOI: 10.1002/14651858.CD007424.pub2.
Disclosures: Dr. Brazzelli reports no disclosures.Dr. Sandercock serves as a member of the Data and Safety Monitoring Board (DSMB), UK for three stroke clinical trials; serves as a Coordinating Editor for the Cochrane Stroke Group, UK; receives research grants from the Medical Research Council, UK (EME 09/800/15) and the National Institute for Health Research (NIHR), UK (EME 08-43-52) for stroke and imaging research. Dr. Wardlaw is Professor of Neuroradiology at the University of Edinburgh, UK; receives research funding from the Scottish Funding Council, UK, the National Institute for Health Research Emerging Medicines Evaluation, UK, and the Scottish Funding Council SPIRIT Scheme, UK; received research support from Wyeth/TMRI Ltd the Row Fogo Trust (AD.ROW4.35, R35865), the UK Stroke Association (TSA 2006/11), the Wellcome Trust, UK (088134/Z/09) for independent academic imaging research.