What is the purpose of the National Institutes of Health Stroke Scale (NIHSS)?

Purpose of the NIH Stroke Scale

The NIH Stroke Scale (NIHSS) is a standardized assessment tool designed to quantify stroke severity, guide acute treatment decisions (particularly thrombolytic therapy eligibility), and predict patient outcomes, with scores >16 indicating high probability of death or severe disability and scores <6 forecasting good recovery. 1, 2

Primary Clinical Functions

The NIHSS serves three critical purposes in stroke management:

1. Severity Stratification and Prognosis

• The scale strongly predicts likelihood of recovery after stroke, with initial scores highly correlated with functional outcomes 1, 3
• Scores >16 forecast high probability of death or severe disability, while scores <6 forecast good recovery 1, 2, 3
• During the first week after acute ischemic stroke, the NIHSS identifies patients highly likely to have poor outcomes 1, 2
• The scale correlates with initial infarct volume, cerebral perfusion, and functional outcome 4

2. Treatment Decision-Making

• The NIHSS guides decisions concerning acute stroke therapy, most importantly determining eligibility for thrombolytic treatment 1, 2, 3
• A 4-point improvement or worsening may alter treatment eligibility 3
• The scale is used on admission to determine patient eligibility for thrombolytic therapy and throughout the acute hospital stay 4

3. Standardized Assessment and Monitoring

• The scale provides objective, reproducible assessment requiring only 5-10 minutes to administer 1, 2
• It is based solely on examination with no historical information needed, allowing any trained clinician to perform it 1, 2
• High inter-rater reliability between examiners makes it highly reproducible across different healthcare settings 2

Recommended Assessment Timepoints

The American Heart Association recommends performing the NIHSS at three critical junctures:

• At presentation/hospital admission or within the first 24 hours 1, 2, 3
• At acute care discharge 1, 2, 3
• Upon transfer to rehabilitation if previous scores are unavailable 1, 2

The second assessment serves as a recheck and may be more accurate because the patient will have stabilized and can better cooperate with the examiner 1

Scale Structure and Administration

• The scale consists of 11 original items assessing various neurological domains including consciousness, visual fields, gaze, facial palsy, motor function, sensation, language, dysarthria, and extinction/inattention 1, 2, 3
• Scores range from 0 to 42, with higher scores indicating more severe strokes 2, 5
• An additional item examining finger extension is often added to assess distal upper extremity weakness, which is more common than proximal arm weakness, though it doesn't contribute to the total score 1, 2

Critical Limitations and Caveats

The NIHSS significantly underestimates posterior circulation stroke severity because symptoms like vertigo, dysphagia, and ataxia are not included in the assessment 2, 3

• 71% of posterior circulation stroke patients present with NIHSS ≤4, yet 15% of these "minor" strokes result in poor outcomes at 3 months 2, 6
• The optimal NIHSS cutoff for outcome prediction is 4 points higher in anterior circulation (8 points) compared to posterior circulation (4 points) 6
• Thrombolytic treatment should not be withheld based solely on low NIHSS scores in posterior circulation strokes 2, 6
• Distal motor function and balance/gait disorders are not adequately covered by the standard scale 3
• Two items (facial palsy and dysarthria) demonstrate lower inter-rater reliability compared to other components 3, 7

Training Requirements

All professionals involved in any aspect of stroke care should be trained and certified to assess stroke severity using the NIHSS 1, 2, 3

• Certification is achieved by watching a training videotape and passing an examination that involves scoring patients shown on a test tape 1, 3
• Proper training ensures accurate assessment and maintains the scale's high inter-rater reliability 2