Combining MRI with NIHSS thresholds to predict outcome in acute ischemic stroke: value for patient selection

Abstract

Background and purpose: Selecting acute ischemic stroke patients for reperfusion therapy on the basis of a diffusion-perfusion mismatch has not been uniformly proved to predict a beneficial treatment response. In a prior study, we have shown that combining clinical with MR imaging thresholds can predict clinical outcome with high positive predictive value. In this study, we sought to validate this predictive model in a larger patient cohort and evaluate the effects of reperfusion therapy and stroke side.

Materials and methods: One hundred twenty-three consecutive patients with anterior circulation acute ischemic stroke underwent MR imaging within 6 hours of stroke onset. DWI and PWI volumes were measured. Lesion volume and NIHSS score thresholds were used in models predicting good 3-month clinical outcome (mRS 0-2). Patients were stratified by treatment and stroke side.

Results: Receiver operating characteristic analysis demonstrated 95.6% and 100% specificity for DWI > 70 mL and NIHSS score > 20 to predict poor outcome, and 92.7% and 91.3% specificity for PWI (mean transit time) < 50 mL and NIHSS score < 8 to predict good outcome. Combining clinical and imaging thresholds led to an 88.8% (71/80) positive predictive value with a 65.0% (80/123) prognostic yield. One hundred percent specific thresholds for DWI (103 versus 31 mL) and NIHSS score (20 versus 17) to predict poor outcome were significantly higher in treated (intravenous and/or intra-arterial) versus untreated patients. Prognostic yield was lower in right- versus left-sided strokes for all thresholds (10.4%-20.7% versus 16.9%-40.0%). Patients with right-sided strokes had higher 100% specific DWI (103.1 versus 74.8 mL) thresholds for poor outcome, and the positive predictive value was lower.

Conclusions: Our predictive model is validated in a much larger patient cohort. Outcome may be predicted in up to two-thirds of patients, and thresholds are affected by stroke side and reperfusion therapy.

Fig 1.

Baseline imaging volumes and NIHSS scores of patients with good (mRS 0–2) and poor (mRS 3–6) clinical outcome at 90 days after stroke. Horizontal lines indicate the thresholds used to predict outcome with DWI (A) (>70 mL MTT predicts poor outcome), NIHSS score (B) (<8 or >20 predicts good or poor outcome, respectively), MTT (C) (<50 mL predicts good outcome), and Tmax (D) (<50 mL predicts good outcome). The filled circles mark patients for whom prediction was incorrect.

Fig 2.

Baseline infarct volumes, clinical status, and probability for poor outcome in treated-versus-untreated patients. A, Mean DWI volume (left) and NIHSS score (right) in patients with good outcome stratified by treatment; asterisks indicate a significant difference. B, Probability (determined by logistic regression) for poor outcome versus DWI plots between untreated and treated patients (black circles represent untreated; gray circles, treated).

Fig 3.

Baseline infarct volumes, probability for poor outcome, and NIHSS score thresholds in left- versus right-sided strokes. A, Mean DWI volume in patients with good outcome stratified by side of involvement. Asterisks indicate a significant difference. B, Probability (determined by logistic regression) for poor outcome versus DWI plots between left- and right-sided strokes (left = black circles, right = gray circles). C, NIHSS score scatterplots and thresholds stratified by side of involvement.