What does NIHSS (National Institutes of Health Stroke Scale) score mean?

Understanding the NIHSS Score

The National Institutes of Health Stroke Scale (NIHSS) is a standardized, validated assessment tool that quantifies neurological deficits in stroke patients, with scores ranging from 0 to 42, where higher scores indicate greater stroke severity and predict worse outcomes in terms of mortality and disability.

What the NIHSS Measures

The NIHSS is an 11-item scale that evaluates specific neurological functions:

1. Level of consciousness (alertness, orientation, and following commands)
2. Best gaze (horizontal eye movements)
3. Visual fields
4. Facial palsy
5. Motor arm strength (both sides)
6. Motor leg strength (both sides)
7. Limb ataxia
8. Sensory function
9. Language abilities
10. Dysarthria (speech clarity)
11. Extinction and inattention

Clinical Significance of NIHSS Scores

The NIHSS score provides critical prognostic information that guides treatment decisions:

• 0-5 points: Mild stroke with good prognosis
• 6-15 points: Moderate stroke
• ≥16 points: Severe stroke with poor prognosis 1

More specifically:

• Score <6: Forecasts good recovery
• Score >16: Forecasts high probability of death or severe disability 1
• Score >20: Indicates a large stroke 1

Research shows that patients with an NIHSS score ≥16 have a 17% risk of intracerebral hemorrhage after thrombolytic treatment, while those with scores <10 have significantly lower risk 1.

Clinical Applications

The NIHSS serves multiple purposes in stroke management:

1. Initial assessment: Strongly recommended within the first 24 hours of presentation 1
2. Treatment decisions: Guides acute interventions, particularly thrombolytic therapy 1
3. Monitoring: Recommended at discharge from acute care to track progress 1
4. Prognosis: Strongly predicts likelihood of recovery and mortality 1, 2

Important Considerations and Limitations

• The NIHSS was designed primarily for anterior circulation strokes and may underestimate the severity of posterior circulation strokes 1
• Symptoms like vertigo or difficulty swallowing (common in posterior circulation strokes) are not included in the NIHSS evaluation 1
• Administration time is approximately 5-8 minutes 3
• Certification is required for proper administration, which involves watching training videos and passing an examination 1
• Inter-rater reliability between examiners for most items is high, making the scale highly reproducible 1

Clinical Pitfalls to Avoid

1. Delay in assessment: Lower NIHSS scores (milder strokes) are associated with longer door-to-needle times for thrombolytic therapy, potentially delaying critical treatment 4

2. Misinterpretation in posterior circulation strokes: Standard NIHSS may underestimate severity in vertebrobasilar strokes 5

3. Failure to reassess: Single assessments may miss neurological progression. Studies show that patients with initial NIHSS scores >7 have a 65.9% chance of neurological worsening in the first 48 hours versus 14.8% for those with scores ≤7 6

4. Improper training: All healthcare professionals involved in stroke care should be trained and certified in NIHSS assessment to ensure accuracy 1

The NIHSS has become an essential tool in stroke management, providing standardized information that helps healthcare teams communicate effectively about stroke severity and make evidence-based treatment decisions that directly impact patient mortality and quality of life.