MRI for unwitnessed stroke looking promising

Feb 22 2016

By Eleanor McDermid

Results of the MR WITNESS study suggest that magnetic resonance imaging (MRI) may be able to identify patients with strokes that can be treated with tissue plasminogen activator (tPA), even if the time of symptom onset is unknown.

The 80 patients in the trial received tPA a median of 11.3 hours after they were last observed without stroke symptoms; 71% had woken up with symptoms.

All patients had evidence of a lesion on diffusion-weighted imaging (DWI), but not on fluid-attenuated inversion recovery (FLAIR), with a signal intensity ratio between the lesion area and unaffected tissue of less than 1.15. This DWI-positive/FLAIR-negative pattern is believed to identify patients within 3 hours of stroke onset, so they were given tPA.

Just one patient developed symptomatic intracerebral haemorrhage (ICH) within 24 hours of treatment, giving a rate of 1.25%, which compared well to the 5.30% rate reported in the European Cooperative Acute Stroke Study (ECASS)3 and therefore met the MR WITNESS study's primary endpoint.

The rate of asymptomatic ICH was also equivalent to that in ECASS3, at 26.3% and 21.8%, respectively, Lee Schwamm (Massachusetts General Hospital, Boston, USA) reported at the International Stroke Conference in Los Angeles, California, USA.

In all, 43.5% of the 69 patients who had no disability (modified Rankin Scale [mRS] 0-1) before stroke still had no disability at 90 days after stroke. Again, this was comparable to rates reported in randomised trials and observational studies of tPA within a 4.5-hour window.

After accounting for confounders, the presence of lacunes, current smoking and more severe stroke reduced the likelihood of achieving mRS 0-1 at 90 days. More severe stroke also increased the likelihood of asymptomatic ICH, as did a shorter time between when patients were last seen well and their arrival at the hospital.

The study did not include placebo-treated controls, but Schwamm pointed to the ongoing randomised WAKE-UP trial, which is testing tPA versus placebo in MRI-selected patients with stroke symptoms on waking.

He also conceded that the use of MRI reduces the generalizability and applicability of the findings, but noted that the planned I-WITNESS trial will test computed tomography versus MRI in patients with unwitnessed stroke.

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