What is the significance of NIHSS (National Institutes of Health Stroke Scale) scores in acute stroke management?

NIHSS Scores in Acute Stroke Management

The NIHSS is the essential standardized tool for assessing stroke severity at presentation, guiding thrombolytic therapy decisions, and predicting patient outcomes, with scores >16 indicating high probability of death or severe disability and scores <6 forecasting good recovery. 1, 2

Core Purpose and Clinical Utility

The NIHSS serves three critical functions in acute stroke care:

• Treatment decision-making: The scale directly determines eligibility for thrombolytic therapy and guides acute intervention strategies 2
• Prognostic stratification: Initial scores strongly predict likelihood of recovery, with a 4-point change potentially altering treatment eligibility 2
• Standardized communication: The scale provides reproducible assessment across different clinicians and healthcare settings with high inter-rater reliability 1

Scale Structure and Administration

The NIHSS consists of 11 core items evaluating neurological domains including level of consciousness, visual fields, gaze, facial palsy, motor function, sensation, language, dysarthria, and extinction/inattention, with scores ranging from 0 to 42 1, 2:

• Administration time: Takes only 5-10 minutes to complete 1
• Objective assessment: Based solely on examination without requiring historical information 1
• Additional item: Finger extension assessment is often added to evaluate distal upper extremity weakness 1

Critical Assessment Timepoints

Perform the NIHSS at three mandatory intervals: 1, 2

1. At presentation/hospital admission (or within first 24 hours)
2. At acute care discharge
3. Upon transfer to rehabilitation if previous scores unavailable

Prognostic Thresholds

The NIHSS provides clear outcome predictions based on specific score ranges 1, 2:

• Score <6: Forecasts good recovery
• Score 7-15: Indicates moderate stroke severity
• Score >16: Forecasts high probability of death or severe disability
• Score >20: Indicates large stroke with poor prognosis 3

Research validates these thresholds, with one study showing 14.9% of cases scored 0-6 points (good), 29.1% scored 7-15 points (moderate), and 56% scored ≥16 points (poor), with significant association between NIHSS score and mortality 4

Training Requirements

All professionals involved in stroke care must be trained and certified in NIHSS administration by watching training videos and passing an examination that involves scoring patients shown on a test tape 1, 2

Critical Limitations and Pitfalls

Posterior Circulation Stroke Underestimation

The NIHSS significantly underestimates posterior circulation stroke severity because symptoms like vertigo, dysphagia, and balance disorders are not adequately covered 2:

• Lower cutoff thresholds needed: The optimal NIHSS cutoff for predicting outcomes is 4 points in posterior circulation strokes versus 8 points in anterior circulation strokes 5
• Risk of withholding treatment: 71% of posterior circulation stroke patients present with NIHSS ≤4, yet 15% of these "minor" stroke patients had poor outcomes at 3 months 5
• Clinical implication: Do not withhold thrombolytic treatment from posterior circulation stroke patients based solely on low NIHSS scores 5

Other Assessment Gaps

• Distal motor function: Not adequately assessed by standard scale 2
• Lower inter-rater reliability: Facial palsy and dysarthria items show reduced reliability compared to other components 2

Motor Assessment Specifics

When scoring motor arm function (Item 5), use precise criteria 3:

• Score 0: No drift (arm holds 90° for full 10 seconds)
• Score 1: Drift (arm holds 90° but drifts down before 10 seconds)
• Score 2: Some effort against gravity (cannot maintain 90° but has effort against gravity)
• Score 3: No effort against gravity (arm falls)
• Score 4: No movement at all

Common pitfall: Do not confuse score 3 (some movement without antigravity effort) with score 4 (complete absence of movement) 3

Predicting Early Progression

The initial NIHSS score predicts likelihood of neurological worsening in the first 48 hours 6:

• NIHSS ≤7: 14.8% progression rate, with 45% achieving functional normality by 48 hours
• NIHSS >7: 65.9% progression rate, with only 2.4% returning to normal examination within 48 hours

A cutoff of NIHSS ≥10.5 demonstrates the best predictive performance for non-neurological in-hospital complications including dysphagia, aspiration pneumonia, and urinary tract infections 7