MRI May Help Predict Which Stroke Patients Benefit Most From Endovascular Therapy

Combining MRI with patient characteristics may be useful for selecting acute stroke patients likely to benefit from endovascular therapy, according to a study published online November 2, 2015, ahead of print in JAMA Neurology. The study authors say the combination method results in a greater proportion of patients who are screened being treated. 

A series of randomized clinical trials published in the past year is stoking renewed excitement for mechanical thrombectomy for major ischemic stroke, but how best to identify patients who might benefit from the therapy remains an unanswered question.

Investigators led by Thabele M. Leslie-Mazwi, MD, of Massachusetts General Hospital (Boston, MA) tested a strategy of combining MR-based measurements of ischemic core size with patient-level characteristics in 72 consecutive stroke patients undergoing endovascular therapy at their center from 2012 through 2014. In a secondary analysis, investigators also looked a group of 31 patients with similar ischemic stokes who were sent for endovascular treatment following CT evaluation, but without additional MRI—either because they were unable to undergo the imaging test itself, or because they presented early, with “reassuring” findings, most notably no evidence of a large infarct on head CT.

In a telephone interview with TCTMD, Leslie-Mazwi explained that patients were classified as ‘likely to benefit’ (n = 40) or ‘uncertain to benefit’ (n = 32) based on a combination of “our clinical experience, our published experience, and others’ published experience.” The criteria have been used in a prospective fashion at their center since the end of 2011, he added.

To be categorized as ‘likely to benefit,’ patients had to be < 80 years old, have a time from stroke onset or last seen well to groin puncture of < 6 hours, had a premorbid mRS score of 1 or less, a life expectancy greater than 12 months, and MRI findings indicating a lesion volume < 70 mL. Those deemed ‘uncertain to benefit’ met 1 or more of the following criteria: age 80 or older, a 6- to 8-hour time from stroke onset, a premorbid mRS score of 2 to 3, a life expectancy of 6 to 12 months, or a lesion volume of 70 to 100 mL.

At 3 months, more patients initially classified as ‘likely to benefit’ did, indeed, have a favorable outcome (defined as a return to complete functional independence) compared with those classified as ‘uncertain to benefit.’ Successful reperfusion resulted in even higher rates of favorable outcomes in this group.

Likewise, patients whose clinical and MR findings at baseline put them in the “unlikely to benefit” category had worse outcomes, even when reperfusion was successful, than patients in whom a benefit was predicted at the outset. Of note, outcomes were similar between the CT-only group and those considered ‘uncertain to benefit.’

“CT alone just is not that great at identifying who will benefit,” Leslie-Mazwi said. “If you have a sample that is selected based on CT with no hemorrhage in the presence of an occlusion, which is the criteria that MR CLEAN and REVASCAT used, you’re going to dilute out that sample with a variety of people who are never going to benefit.”

Across all three groups, failure of reperfusion despite attempted thrombectomy was associated with poor outcomes; mRS scores of 0 to 2 occurred in only 1 of 13 ‘likely to benefit’ patients with failed reperfusion and in none of 8 ‘uncertain to benefit patients.’

More Screened Patients Treated Than with CT

Leslie-Mazwi and colleagues say their ‘likely to benefit’ cohort closely resembled patients enrolled in other endovascular stroke therapy trials, including EXTEND-IA, ESCAPE,  and SWIFT PRIME. Those trials had rates of favorable outcomes ranging from 53% to 71%, but they selected patients with small ischemic cores using advanced imaging beyond identifying an occlusion by CTA to get “the cream of the crop,” Leslie-Mazwi noted. MR CLEAN and REVASCAT relied solely on CT and had low rates of favorable outcomes (33% and 44%, respectively).

“We applied diffusion MRI for the same purpose and screened 3 patients for each patient treated, whereas in EXTEND-IA and SWIFT PRIME a mean of 14 and 7.5 patients, respectively, were screened to select a patient for treatment,” Leslie-Mazwi and colleagues write. “The outcomes of the clinical trials and our prospective observational study suggest that there is a trade-off between maximizing the favorable outcome rate with endovascular treatment and the selection rate of those patients.”

Leslie-Mazwi added that he believes MRI confers more precision and helps extend screening to people who otherwise might be excluded.    

The study is not the first to utilize MRI in this patient population. SWIFT PRIME included a small cohort of patients imaged with MRI, but outcome data on those patients have not been published.

According to Leslie-Mazwi, MRI may be more useful than CT in evaluating eligibility of patients with other types of stroke as well, including posterior and distal strokes, and those in the so-called “late window” with strokes of later onset.

DEFUSE-3, currently underway, is using MRI in patients with acute ischemic anterior circulation strokes due to large artery occlusion who will be randomized to thrombectomy or control as far out as 16 hours from stroke onset, Leslie-Mazwi noted.

“The signal is not going to be as loud in that later time window,” he said. “So the way of identifying those patients has to be even more refined, and that’s where MRI comes in.”

Source: 
Leslie-Mazwi TM, Hirsch JA, Falcone GJ, et al. endovascular stroke treatment outcomes after patient selection based on magnetic resonance imaging and clinical criteria. JAMA Neurol. 2015;Epub ahead of print. 

Disclosures:

• Leslie-Mazwi reports no relevant conflicts of interest. 

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