What is the NIH Stroke Scale (National Institutes of Health Stroke Scale) and how is it used to assess and quantify neurological impairment in acute stroke patients?

NIH Stroke Scale: Assessment Tool for Acute Stroke

The NIH Stroke Scale (NIHSS) is a standardized 11-item neurological examination that quantifies stroke severity on a 0-42 point scale, taking only 5-10 minutes to administer, and should be performed at presentation, within 24 hours of admission, and at discharge to guide acute treatment decisions and predict patient outcomes. 1, 2

Scale Structure and Components

The NIHSS evaluates specific neurological domains through systematic examination 3:

• Consciousness assessment: Level of alertness, orientation (month, age), and ability to follow commands 2
• Visual function: Visual field deficits and gaze abnormalities 3, 2
• Motor function: Facial palsy, arm and leg motor strength (tested by holding arms at 90 degrees for 10 seconds, scoring based on drift and effort against gravity) 3, 2
• Sensory function: Sensation to pinprick 2
• Language and speech: Aphasia assessment through picture description, object naming, and sentence reading; dysarthria evaluation 3, 2
• Attention: Extinction and inattention 2

An additional item assessing finger extension is often added to evaluate distal upper extremity weakness, which is more common than proximal weakness in stroke patients 1.

Administration Requirements

All clinicians involved in stroke care must be trained and certified in NIHSS administration by watching training videos and passing a standardized examination. 1, 2 The scale requires no historical information or surrogate input—it is based solely on objective examination findings 1.

Critical Timing of Assessment

The NIHSS must be performed at three specific timepoints 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)

Clinical Applications and Treatment Decisions

The NIHSS directly guides acute stroke therapy decisions, particularly thrombolytic therapy eligibility 1, 2. A 4-point improvement or worsening from baseline may alter treatment eligibility and should prompt reassessment before intervention 3, 2.

Prognostic Value

The initial NIHSS score strongly predicts patient outcomes 1, 2, 4:

• Score >16: High probability of death or severe disability 1, 2
• Score <6: Good recovery expected 1, 2
• Score ≤7: Only 14.8% experience early neurological worsening; 45% achieve functional normality within 48 hours 4
• Score >7: 65.9% experience early neurological worsening; only 2.4% return to normal examination within 48 hours 4

Important Limitations and Caveats

The NIHSS significantly underestimates posterior circulation stroke severity because critical symptoms like vertigo, dysphagia, and ataxia are not included in the assessment. 1 Posterior circulation patients score an average of 2 points higher when assessed with expanded scales, and 71% present with NIHSS ≤4, yet 15% of these "minor" strokes result in poor outcomes at 3 months 1. Therefore, thrombolytic treatment should not be withheld based solely on low NIHSS scores in suspected posterior circulation strokes. 1

Additional limitations include 3, 1, 2:

• Distal motor function and balance/gait disorders are inadequately assessed 3, 1
• Facial palsy and dysarthria items demonstrate lower inter-rater reliability 2, 5
• Limb ataxia shows poor reliability, particularly in telemedicine assessments 2

Telemedicine Administration

The NIHSS can be reliably administered via telemedicine with high-quality video conferencing 3, 6. Remote assessments take slightly longer (mean 9.70 vs 6.55 minutes) but maintain strong correlation with bedside scores (r=0.97) 6. Rearrange the NIHSS order to reduce camera manipulations by performing close-up items before zoomed-out views. 2 Items requiring extra attention during telemedicine assessment include facial palsy, ataxia, and dysarthria due to lower reliability 2.

Modified NIHSS Considerations

A modified 11-item NIHSS (mNIHSS) eliminates poorly reliable items and shows improved inter-rater reliability, with excellent agreement increasing from 54% to 71% and poor agreement decreasing from 12% to 5% compared to the standard scale 5, 7. The mNIHSS performs particularly well in record abstraction, telemedicine, and clinical trial settings 7.