Combining MRI with NIHSS Thresholds to Predict Outcome in Acute Ischemic Stroke: Value for Patient Selection

P.W. Schaefer; B. Pulli; W.A. Copen; J.A. Hirsch; T. Leslie-Mazwi; L.H. Schwamm; O. Wu; R.G. González; A.J. Yoo

doi:10.3174/ajnr.A4103

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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.
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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).
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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.

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Table 1:

Baseline clinical and imaging characteristics, treatment, and predictors of 3-month mRS

	All Patients (n = 123)	mRS 0–2 (n = 68)	mRS 3–6 (n = 55)	P Value
Age (yr)	69.8 ± 15.9	68.9 ± 16.9	70.8 ± 14.7	.727^{^a}
Baseline NIHSS score	11 (6–16)	7 (5–11.5)	16 (14–20.75)	<.0001^{^a}
Female sex	55 (44.7%)	31 (45.6%)	24 (43.6%)	.973^{^b}
Right hemisphere	74 (47.2%)	34 (50.0%)	24 (43.6%)	.602^{^b}
Time to MRI	3:57 ± 1:26	3:45 ± 1:29	4:12 ± 1:20	.085^{^c}
DWI volume (mL)	37.4 ± 47.7	16.3 ± 20.1	63.4 ± 58.2	<.0001^{^a}
MTT volume (mL)	129.5 ± 101.3	80.6 ± 78.3	189.9 ± 94.1	<.0001^{^a}
Tmax volume (mL)	148.1 ± 114.9	89.5 ± 86.5	217.3 ± 106.0	<.0001^{^a}
Absolute mismatch (mL)	92.7 ± 81.4	64.9 ± 69.1	127.1 ± 82.9	<.0001^{^a}
Relative mismatch	8.7 ± 21.6	10.9 ± 27.8	6.0 ± 8.8	.541^{^a}
Reperfusion therapy	None: 37 (30.1%)	22 (32.4%)	15 (25.4%)
	IV-tPA: 61 (49.6%)	36 (52.9%)	25 (45.5%)	.200^{^b}
	IAT ± IV-tPA: 25 (20.3%)	10 (14.7%)	15 (27.3%)
Occlusion level	ICA: 24 (19.5%)	6 (8.8%)	18 (32.7%)
	MCA M1: 39 (31.7%)	15 (22.1%)	24 (43.6%)	<.0001^{^b}
	MCA M2/3: 36 (29.3%)	24 (35.3%)	12 (21.8%)
	None: 24 (19.5%)	23 (33.8%)	1 (1.8%)

Note:—IAT indicates intra-arterial thrombolysis.
↵a Mann-Whitney U test.
↵b χ² test.
↵c Student t test.

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Table 2:

Validation of the previously described model combining clinical and imaging thresholds to predict outcome in acute ischemic stroke

Threshold	Positive Predictive Value (%)	Prognostic Yield (%)
Poor outcome
DWI > 70 mL	86.4^{^a}	17.9
NIHSS score > 20	100.0^{^a}	11.4
Good outcome
MTT < 0 mL	89.5^{^a}	30.9
Tmax < 50 mL	88.9^{^a}	29.3
NIHSS score < 8	92.3^{^a}	31.7
Combined clinical thresholds (NIHSS score)	94.3^{^a}	43.1
Combined imaging thresholds (DWI + MTT)	88.3^{^a}	48.8
Combined imaging thresholds (DWI + Tmax > 6 seconds)	87.9^{^a}	47.2
Combined clinical and imaging thresholds	88.8^{^a}	65.0^{^b}

↵a No significant difference in PPV between any of the applied thresholds.
↵b Significantly increased over use of single parameters (P < .0001) and combined clinical or imaging thresholds (P = .01).

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Table 3:

Differences of clinical and imaging thresholds in patients receiving thrombolysis versus untreated patients

	No Reperfusion Therapy	IV and/or IA Therapy	P Value
DWI
AUC ± SE for predicting poor outcome	0.935 ± 0.06	0.724 ± 0.05	.011
90% Specificity for poor outcome (prognostic yield) (mL)	>19.7 (42.3%)	>51.8 (19.5%)	.016^{^a}
95% Specificity for poor outcome (prognostic yield) (mL)	>20.5 (40.5%)	>74.8 (16.1%)	.007^{^a}
	>30.6 (35.1%)	>103.1 (10.4%)	.003^{^a}
NIHSS score
AUC ± SE for predicting poor outcome	0.903 ± 0.06	0.827 ± 0.04	.314
90% Specificity for poor outcome (prognostic yield)	>12 (37.8%)	>16 (23.0%)	.142^{^a}
95% Specificity for poor outcome (prognostic yield)	>15 (27.0%)	>19 (14.9%)	.182^{^a}
100% Specificity for poor outcome (prognostic yield)	>17 (16.2%)	>20 (9.2%)	.414^{^a}

↵a P value for comparison among prognostic yields.

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Table 4:

Differences of clinical and imaging thresholds in patients stratified by affected cerebral hemisphere

	Right Side	Left Side	P Value
DWI
AUC ± SE	0.706 ± 0.07	0.875 ± 0.04	.043
90% Specificity for poor outcome (prognostic yield) (mL)	>39.6 (20.7%)	>23.4 (40.0%)	.034^{^a}
95% Specificity for poor outcome (prognostic yield) (mL)	>98.5 (12.1%)	>51.8 (26.2%)	.082^{^a}
100% Specificity for poor outcome (prognostic yield) (mL)	>103.1 (10.4%)	>74.8 (16.9%)	.435^{^a}
NIHSS score
AUC ± SE	0.808 ± 0.06	0.911 ± 0.03	.077
90% Specificity for poor or good outcome (prognostic yield)	>15 or <6 (29.3%)	>17 or <10 (66.2%)	<.001^{^a}
95% Specificity for poor or good outcome (prognostic yield)	>16 or <5 (17.2%)	>20 or <9 (49.2%)	<.001^{^a}
100% Specificity for poor or good outcome (prognostic yield)	>16 or <3 (1.7%)	>20 or <7 (38.5%)	<.001^{^a}