What is the National Institutes of Health Stroke Scale (NIHSS) and how is it used to assess stroke severity and guide acute treatment decisions?

National Institutes of Health Stroke Scale (NIHSS)

The NIHSS is a standardized 11-item neurological examination that takes 5-10 minutes to complete, scores from 0-42 points, and serves as the primary tool for determining thrombolytic therapy eligibility and predicting stroke outcomes, with scores >16 forecasting high probability of death or severe disability and scores <6 forecasting good recovery. 1, 2

Core Purpose and Clinical Applications

The NIHSS was developed by stroke neurologists from the University of Cincinnati, University of Iowa, and NIH-NINDS specifically to quantify neurological impairment after stroke. 3 It functions as the most widely used stroke deficit scale among stroke neurologists and neuroscience nurses, providing objective assessment based solely on examination without requiring historical information or family input. 2

The scale directly guides acute treatment decisions, particularly eligibility for thrombolytic therapy, with a change of ±4 points from baseline potentially altering treatment eligibility and requiring reassessment before proceeding. 1, 2

Scale Components and Scoring

The NIHSS evaluates 11 core domains: 1, 2

• Level of consciousness - assessed through patient response to stimulation, orientation questions, and ability to follow commands 1
• Visual fields and gaze - these items demonstrate excellent reliability in both bedside and telemedicine assessments 1
• Facial palsy - though this item shows lower inter-rater reliability compared to other components 1
• Motor arm function - patient extends arms palm down at 90 degrees (sitting) or 45 degrees (supine) and holds for 10 seconds, with scoring: 0=no drift, 1=drift before 10 seconds, 2=some effort against gravity but cannot maintain position, 3=no effort against gravity (arm falls), 4=no movement at all 1, 4
• Motor leg function - assessed similarly to arm function 2
• Limb ataxia - demonstrates lower inter-rater reliability, particularly in telemedicine assessments 1
• Sensory function - evaluated through response to pinprick 1
• Language/aphasia - patient describes standardized pictures, names objects, and reads sentences, scored on fluency and comprehension 1
• Dysarthria - has lower inter-rater reliability and requires extra attention during assessment 1
• Extinction and inattention 1

An optional finger extension item is often added to assess distal upper extremity weakness but is not included in the total score. 2

Mandatory Assessment Timepoints

The American Heart Association mandates NIHSS assessment at three critical timepoints: 1, 2

1. At presentation/hospital admission or within first 24 hours - establishes baseline stroke severity and determines thrombolytic eligibility 2
2. Immediately before any therapeutic intervention - serves as re-check when patient is stabilized and can cooperate better 2
3. At acute care discharge - measures neurological functional improvement 1, 2

If a patient transfers to rehabilitation without documented scores, the rehabilitation team must complete an NIHSS assessment. 2

Training and Certification Requirements

All professionals involved in any aspect of stroke care must be trained and certified in NIHSS administration by watching training videos and passing a competency examination. 3, 1, 2 This certification ensures accurate severity assessment and reduces inter-observer variability, as the scale demonstrates high inter-rater reliability between properly trained examiners. 2

Certification resources are available at www.strokeassociation.org or www.ninds.nih.gov. 3

Prognostic Value and Clinical Decision-Making

The NIHSS strongly predicts patient outcomes: 1, 2

• Scores >16 indicate high probability of death or severe disability 1, 2
• Scores <6 forecast good recovery 1, 2
• Scores >20 indicate large strokes with poor prognosis 4
• Within the first week after acute ischemic stroke, the NIHSS identifies patients highly likely to experience poor outcomes 2

Research demonstrates that patients with initial NIHSS ≤7 experience only 14.8% worsening rate versus 65.9% worsening in those with scores >7, suggesting a critical dichotomy at score of 7 for early clinical course prediction. 5

Critical Limitations and Pitfalls

The NIHSS significantly underestimates posterior circulation stroke severity because symptoms like vertigo, dysphagia, and ataxia are not included in the assessment. 2 Posterior circulation patients evaluated with expanded NIHSS versions score an average of 2 points higher than with classical NIHSS, and 71% of posterior circulation stroke patients present with NIHSS ≤4, yet 15% of these "minor" strokes result in poor outcomes at 3 months. 2

Additional limitations include: 1, 2

• Distal motor function and balance/gait disorders are inadequately covered 1
• Facial palsy and dysarthria items demonstrate lower inter-rater reliability 1
• Limb ataxia shows poor reliability, especially via telemedicine 1
• The scale was originally designed primarily for anterior circulation ischemic strokes 2

Common assessment pitfall: Do not confuse a score of 3 (no effort against gravity but some movement) with score of 4 (no movement at all) when assessing motor function. 4

Telemedicine Administration

The NIHSS can be administered remotely with high-quality video conferencing, yielding strong correlation with bedside scores (Pearson r=0.97), though remote assessments take slightly longer (mean 9.7 minutes versus 6.55 minutes in-person). 1 The American Heart Association recommends rearranging the NIHSS order to reduce camera manipulations, performing close-up items before zoomed-out views. 1

Blood Pressure Management Context

When using NIHSS to guide acute stroke management, blood pressure elevations are generally not treated unless diastolic BP >120 mmHg or systolic BP >220 mmHg in patients not receiving thrombolytics, to facilitate adequate cerebral perfusion pressure. 3 For patients treated with intravenous thrombolysis, stricter blood pressure parameters apply based on NIH-NINDS rtPA trial data. 3