What is the NIHSS?
The National Institutes of Health Stroke Scale (NIHSS) is a standardized, validated 11-item neurological examination tool that quantifies stroke severity on a 0-42 point scale, where higher scores indicate more severe neurological impairment. 1, 2, 3
Core Purpose and Clinical Applications
The NIHSS serves as the primary tool for guiding acute stroke treatment decisions, including eligibility for thrombolytic therapy, and strongly predicts patient outcomes after stroke. 4, 2, 3
The scale takes only 5-10 minutes to administer and is based solely on physical examination without requiring historical information or input from family members. 3
Scores are interpreted prognostically: scores >16 forecast high probability of death or severe disability, scores <6 forecast good recovery, and scores between 7-15 indicate moderate severity. 4, 2, 5
Scale Components
The NIHSS evaluates 11 core domains of neurological function: 2, 3
Level of consciousness (alertness, orientation, commands)
Visual fields
Extraocular movements/gaze
Facial palsy
Motor arm function (both sides)
Motor leg function (both sides)
Limb ataxia
Sensory function
Language/aphasia
Dysarthria
Extinction and inattention
An additional item assessing finger extension is often added to better capture distal upper extremity weakness, which is more common than proximal weakness in stroke patients. 3
When to Perform the NIHSS
All stroke patients should be assessed using the NIHSS at three critical timepoints: 4, 2, 3
- At presentation/hospital admission (or at minimum within the first 24 hours)
- At acute care discharge
- Upon transfer to rehabilitation if no previous scores are documented
Training and Certification Requirements
All healthcare professionals involved in stroke care—including physicians, nurses, therapists, and social workers—should be trained and certified in NIHSS administration. 4, 2, 3
Certification is achieved by watching training videotapes and passing an examination that involves scoring patients shown on test videos. 4, 3
The scale demonstrates high inter-rater reliability between certified examiners, making it highly reproducible across different healthcare settings. 4, 3
Critical Limitations and Pitfalls
The NIHSS significantly underestimates posterior circulation stroke severity because key symptoms like vertigo, dysphagia, and ataxia are not adequately assessed. 2, 3, 6
71% of posterior circulation stroke patients present with NIHSS scores ≤4, yet 15% of these "minor" strokes result in poor outcomes at 3 months. 3, 6
The optimal NIHSS cutoff for predicting poor outcomes is 4 points lower in posterior circulation strokes (cutoff = 4) compared to anterior circulation strokes (cutoff = 8). 6
Thrombolytic treatment should not be withheld from posterior circulation stroke patients based solely on low NIHSS scores. 3, 6
Two specific items—facial palsy and dysarthria—have demonstrated lower inter-rater reliability compared to other components. 2
Distal motor function and balance/gait disorders are not adequately covered by the standard scale. 2
Clinical Significance for Treatment Decisions
The NIHSS determines eligibility for thrombolytic therapy in acute stroke management. 2
A 4-point improvement or worsening on the NIHSS may alter treatment eligibility and guide clinical decision-making. 2
Baseline NIHSS scores have a profound association with mortality after acute stroke, with mortality rates increasing significantly as scores rise above 16 points. 5