New tool predicts stroke outcomes

Scientists have developed a new tool that may help physicians predict, during the first several hours a stroke patient is in the hospital, the degree of recovery the patient will eventually experience. The tool uses three factors for the accurate prediction of stroke outcome: measurement of brain injury using magnetic resonance imaging, the patient's score on the National Institutes of Health Stroke Scale, and the time in hours from the onset of symptoms until the MRI brain scan is performed.

"We hope this new tool will not only help physicians manage their patients more efficiently, but also will alleviate the distress and anxiety about prognosis that patients and their families suffer in the first days after stroke," said Alison E. Baird, an author of the study, which was published in The Lancet (vol. 357, no. 9274).

The researchers set out to see whether a new type of brain imaging technology called magnetic resonance diffusion-weighted imaging, in addition to standard clinical assessments, could yield prognostic information about a stroke. The MR-DWI can measure the volume of the lesions that appear during the first few hours after an ischemic stroke, which is caused by a clot obstructing blood flow to the brain. The study results showed that this measurement correlates with the severity of the stroke, as well as the patient's outcome. Patients with small lesion volumes (less than 14.1 milliliters) were five times more likely to recover from their strokes than patients with larger lesion volumes.

The Stroke Scale

Another important prognostic tool that has been used widely for many years is the National Institutes of Health Stroke Scale, which is used to measure the severity of neurological dysfunction at the time of a stroke. In the study reported in The Lancet, the Stroke Scale was measured within one hour of the MRI scan. A score greater than 25 indicates very severe neurological impairment, a score between 15 and 25 indicates severe impairment, a score between five and 15 indicates mild to moderately severe impairment, and a score less than five indicates mild impairment. The mean score of the patients in this study was 11.

The third measurement in the scale is the time from the onset of the patient's symptoms to the time of the brain scan. If a patient suffered the stroke while asleep, the time was backdated to the last time the patient was known to have no stroke symptoms. Surprisingly, the patients who waited the longest before receiving their scans were more likely to recover. The investigators speculate that this time relationship may reflect an "instability" factor in the earliest hours of stroke. There may be more certainty of a good outcome when the patient is assessed beyond the first six hours, by which time the most critical changes in blood flow in the brain have occurred.

An accurate prediction

The National Institute of Neurological Disorders and Stroke study involved looking at data from a total of 129 stroke patients - 66 at the Boston-based Beth Israel Deaconess Medical Center and 63 at the Royal Melbourne Hospital in Australia - and then developing a three-item scale for early prediction of stroke recovery (good stroke recovery in this study was defined as a score of greater than 90 on the Barthel Index, indicating a patient who has nearly full functional independence).

Using the three-item scale, the researchers assigned points (with a maximum score of 7) based on brain lesion volume, the patient's score on the NIHSS and the time from symptoms to scanning. The clinicians rated patients' likelihood of recovery using categories of low (total score of 0 to 2), medium (total score of 3 to 4) or high (total score of 5 to 7).

The new scale proved to be a very accurate predictor of stroke recovery, with high sensitivity and specificity. In the Boston group, only 6% of the patients who had a low score (0 to 2) recovered, 47% of the patients with a medium-range score recovered and 93% of those with a high score recovered. In the Australian group, 8% of patients with a low score recovered, 57% of patients with a medium score recovered and 78% of patients with a high score recovered.

The researchers concluded that the combination of clinical and imaging data allowed more reliable early prediction of stroke recovery than any single factor alone. PR