National Institutes of Health Stroke Scale score is poorly predictive of proximal occlusion in acute cerebral ischemia

Abstract

Background and purpose: Multimodal imaging is gaining an important role in acute stroke. The benefit of obtaining additional clinically relevant information must be weighed against the detriment of increased cost, delaying time to treatment, and adverse events such as contrast-induced nephropathy. Use of National Institutes of Health Stroke Scale (NIHSS) score to predict a proximal arterial occlusion (PO) is suggested by several case series as a viable method of selecting cases appropriate for multimodal imaging.

Methods: Six hundred ninety-nine patients enrolled in a prospective cohort study involving CT angiographic imaging in acute stroke were dichotomized according to the presence of a PO, including a subgroup of 177 subjects with middle cerebral artery M1 occlusion.

Results: The median NIHSS score of patients found to have a PO was higher than the overall median (9 versus 5, P<0.0001). The median NIHSS score of patients with middle cerebral artery M1 occlusion was 14. NIHSS score > or =10 had 81% positive predictive value for PO but only 48% sensitivity with the majority of subjects with PO presenting with lower NIHSS scores. All patients with NIHSS score > or =2 would need to undergo angiographic imaging to detect 90% of PO.

Conclusions: High NIHSS score correlates with the presence of a proximal arterial occlusion in patients presenting with acute cerebral ischemia. No NIHSS score threshold can be applied to select a subgroup of patients for angiographic imaging without failing to capture the majority of cases with clinically important occlusive lesions. The finding of minimal clinical deficits should not deter urgent angiographic imaging in otherwise appropriate patients suspected of acute stroke.

Figure 1

A histogram depicting the distribution of initial NIHSS scores as a percent of the total for subjects found to have a proximal occlusion and those in whom no proximal occlusion is identified.

Figure 2

This figure graphs the percentage of subjects with proximal occlusions that would have remain undetected if an NIHSS score threshold were applied to select subjects for angiographic imaging.

Figure 3

The receiver operator characteristic curve is shown for use of NIHSS score thresholds to predict proximal occlusion. Points on the curve are labeled with their corresponding NIHSS score.

Figure 4

A histogram of initial NIHSS scores for subjects found to have MCA M1 segment occlusion. Superimposed on the histogram is a graph showing the cumulative percentage of subjects by increasing NIHSS score.