What is the NIHSS Score?
The National Institutes of Health Stroke Scale (NIHSS) is a standardized 42-point assessment tool that quantifies neurological deficits after stroke, where higher scores indicate more severe neurological impairment, and it serves as the primary instrument for guiding acute stroke treatment decisions and predicting patient outcomes. 1, 2
Core Structure and Components
The NIHSS consists of 11 core items that evaluate specific neurological domains including level of consciousness, visual fields, extraocular movements, facial palsy, motor function (arms and legs), sensory function, language, dysarthria, and extinction/inattention 3, 2
The scale ranges from 0 to 42 points total, with each item scored individually based on standardized criteria 1
An additional item assessing finger extension is often added to evaluate distal upper extremity weakness, which is more common than proximal arm weakness in stroke patients 2
Administration takes only 5-10 minutes and is based solely on examination without requiring historical information or input from family members 2
Scoring Interpretation and Prognostic Value
Scores greater than 16 forecast a high probability of death or severe disability, while scores less than 6 forecast good recovery. 1, 3, 2
The scale provides three severity categories: good (0-6 points), moderate (7-15 points), and poor (≥16 points) 4
Initial NIHSS scores strongly predict the likelihood of patient recovery and are used to guide critical decisions about acute stroke therapy, including eligibility for thrombolytic treatment 1, 3
During the first week after acute ischemic stroke, the NIHSS can identify patients highly likely to have poor outcomes 1
Clinical Applications and Timing
The American Heart Association strongly recommends performing the NIHSS at three critical timepoints: at presentation/hospital admission (or within 24 hours), at acute care discharge, and upon transfer to rehabilitation if previous scores are unavailable. 1, 3, 2
A 4-point improvement or worsening from baseline may alter treatment eligibility and should trigger reassessment of the patient's management plan 1, 3
The scale is particularly valuable for stratifying patients according to severity and likely outcome in both clinical practice and research settings 1
Administration Requirements and Certification
All professionals involved in stroke care (physicians, nurses, therapists, social workers) should be trained and certified to administer the NIHSS 1, 3, 2
Certification is achieved by watching a training videotape and passing an examination that involves scoring patients shown on a test tape 1, 2
The scale demonstrates high inter-rater reliability between certified examiners for most items, making it highly reproducible across different healthcare settings 1, 2
Important Limitations and Caveats
The NIHSS was designed primarily for anterior-circulation ischemic stroke evaluation and may underestimate the severity of posterior-circulation strokes. 1, 3
Posterior-circulation symptoms such as vertigo, difficulty swallowing (dysphagia), and balance disorders are not adequately captured by the standard scale 1, 3
Two items—facial palsy and dysarthria—have demonstrated lower inter-rater reliability compared to other components 3
Distal motor function and gait disorders are not comprehensively covered by the standard scale, potentially requiring additional assessments 3
A standardized grading system for posterior-circulation strokes is not currently available, which is a recognized gap in stroke assessment 1
Development and Validation
The NIHSS was developed by researchers at the National Institute of Neurological Disorders and Stroke (NINDS) specifically for use in clinical stroke trials 1
The scale has been extensively validated and standardized to reduce interobserver error across multiple clinical trials 1
Ongoing validation of the predictive value of the NIHSS through prospective data collection is encouraged to maintain its clinical utility 1