NIHSS Score: Clinical Significance and Interpretation
The NIHSS is a standardized 11-item assessment tool that quantifies stroke severity on a 0-42 point scale, with scores >16 predicting high probability of death or severe disability, scores <6 predicting good recovery, and should be performed at presentation, within 24 hours, and at discharge to guide acute treatment decisions including thrombolytic therapy eligibility. 1, 2
Score Ranges and Prognostic Implications
The NIHSS provides clear prognostic stratification that directly impacts clinical decision-making:
- Scores 0-6 (Minor stroke): Forecast good recovery with low probability of severe disability 1, 2
- Scores 7-15 (Moderate stroke): Intermediate severity requiring close monitoring and aggressive rehabilitation 3
- Scores ≥16 (Severe stroke): High probability of death or severe disability, indicating need for intensive interventions 1, 2, 3
Higher scores correlate directly with increased mortality risk, with baseline NIHSS demonstrating profound association with post-stroke mortality (p<0.001) 3
Administration Requirements and Timing
All clinicians involved in stroke care must be trained and certified through standardized video training and examination to ensure high inter-rater reliability 1, 2
Perform NIHSS at three critical timepoints:
- At presentation or within first 24 hours of admission 1, 2
- At acute care discharge 1, 2
- Upon transfer to rehabilitation if previous scores unavailable 1
The assessment takes only 5-10 minutes and requires no historical information, relying solely on objective examination findings 1
Clinical Applications
The NIHSS directly determines eligibility for thrombolytic therapy and guides acute stroke management decisions 2. A 4-point improvement or worsening may alter treatment eligibility 2. The scale's high inter-rater reliability (ICC = 0.99) makes it highly reproducible across different healthcare settings and examiners 1, 4
Critical Limitations and Pitfalls
The NIHSS systematically underestimates posterior circulation stroke severity because key symptoms like vertigo, dysphagia, and ataxia are not included in the assessment 1. Posterior circulation patients score an average of 2 points higher when evaluated with expanded NIHSS versions 1, 5. Critically, 71% of posterior circulation strokes present with NIHSS ≤4, yet 15% of these "minor" strokes result in poor outcomes at 3 months 1
Do not withhold thrombolytic treatment based solely on low NIHSS scores in suspected posterior circulation strokes 1
Additional limitations include:
- Distal motor function and balance/gait disorders inadequately covered 2
- Facial palsy and dysarthria items demonstrate lower inter-rater reliability compared to other components 2, 6
Assessment Components
The scale evaluates 11 core domains including level of consciousness, visual fields, gaze, facial palsy, motor arm and leg function, sensation, language, dysarthria, and extinction/inattention 1, 2. An additional item assessing finger extension is often added to better capture distal upper extremity weakness 1
When distinguishing motor scores, carefully differentiate between score 3 (no effort against gravity but some movement present) versus score 4 (complete absence of movement) 7. For language assessment, even subtle hesitations or circumlocutions indicate mild aphasia rather than normal function 1