Lancet: MRI technique may open window for stroke therapy
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Approximately 25 percent of ischemic stroke patients present with strokes that occurred during sleep, which excludes them from thrombolysis. These patients and others with an unknown time of stroke onset are excluded from therapy as thrombolysis should be administered within a 4.5-hour time window of stroke onset.
Previous research has suggested that mismatched visibility of an acute ischemic lesion between DWI and FLAIR may identify patients likely to be within a three-hour window of stroke onset, according to Gotz Thomalla, MD, of the department of neurology at University of Hamburg in Hamburg, Germany, and colleagues.
Thomalla and colleagues designed a retrospective study to determine if DWI-FLAIR mismatch could estimate lesion age in patients with an unknown time of stroke onset.
Two neurologists reviewed DWI and FLAIR datasets of 543 patients acquired between Jan. 1, 2001, and May 31, 2009, to determine the visibility of lesions on the images. The researchers calculated predictive values of DWI-FLAIR mismatch for identification of stroke within 4.5 and six hours of onset.
Thomalla et al emphasized three primary findings. “We showed that the DWI-FLAIR mismatch can be used to identify patients within 4.5 hours of symptom onset with high specificity and high positive predictive value [78 percent and 83 percent, respectively].” However, at 62 percent, sensitivity was low, indicating the need for studies of additional imaging methods. The researchers also identified several potential confounders that could affect the accuracy of DWI-FLAIR mismatch, including lesion volume and image quality.
“The clinical use of DWI-FLAIR mismatch as a surrogate marker of lesion age could enable the extension of thrombolysis use to a new population of patients who are likely to benefit from treatment. However, patients should not be offered such treatment beyond a time from onset of symptoms during which thrombolysis is safe and effective,” Thomalla and colleagues wrote.
These restrictions require high specificity and positive predictive value. The values derived in the current study met this threshold, the researchers said, and suggest the need for a prospective clinical trial to begin testing the role of DWI and FLAIR imaging and thrombolysis among patients with an unknown time of stroke onset.
An accompanying editorial, authored by Michael D. Hill, MD, and Richard Frayne, MD, of Hotchkiss Brain Institute at University of Calgary in Canada, noted that DWI-FLAIR mismatch may help identify a tissue window that defines salvageable tissue. Thus, an imaging biomarker could identify patients within the 4.5 hour time window who would not benefit from thrombolysis and also those beyond the window who could benefit.