The National Institute of Health Stroke Scale (NIHSS) is a well-validated, highly reproducible tool that is widely used to measure neurologic deficit and as a scoring system for stroke intervention.
This scale is heavily weighted toward recognizing deficit due to anterior circulation strokes, however, while that due to posterior circulation strokes receives fewer points.
One study found that nearly 1% of patients with MRI-confirmed acute ischemic stroke patients scored zero points on the NIHSS, and that the majority of these were posterior strokes. These types were more likely to present with truncal ataxia (most commonly), headache, vertigo, and nausea.
Take home points:(1) The NIHSS should not replace a thorough neurological examination. (2) Consider posterior stroke as the source of persistent symptoms in patients with an NIHSS score of zero.
References
Martin-Schild et al. Zero on the NIHSS does not equal the absence of stroke. Annals of Emergency Medicine. Vol. 57. No. 1. January 2011.
