NIH Stroke Scale (NIHSS)
Quantifies stroke severity to guide acute treatment decisions
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Why use it
Required for thrombolysis eligibility assessment. Predicts stroke outcome and infarct volume. Guides acute treatment decisions (IV tPA, mechanical thrombectomy). Serial NIHSS tracks improvement or deterioration.
About
The NIHSS is a systematic assessment tool that provides a quantitative measure of stroke-related neurological deficit. It evaluates 11 items including level of consciousness, gaze, visual fields, facial palsy, motor function, ataxia, sensory, language, dysarthria, and extinction/inattention. It is the standard tool for determining thrombolytic eligibility and monitoring stroke evolution.
When to use
- Acute stroke assessment in ED
- Before and after thrombolysis (tPA/tenecteplase)
- Thrombectomy candidacy evaluation
- Serial neurological monitoring during stroke hospitalization
Formula
Pearls & pitfalls
- NIHSS certification is required before administering tPA at most centers.
- NIHSS does NOT capture posterior circulation strokes well (vertebrobasilar) — clinical judgment needed.
- Score > 25 associated with high mortality and hemorrhagic transformation risk.
- A 4-point improvement in NIHSS is considered clinically significant.
- NIHSS is weighted toward left hemisphere/dominant functions (language) — right hemisphere strokes may score lower despite severe disability.
- Always document time of NIHSS assessment alongside the score.
Next steps
NIHSS 0: Symptoms resolved, consider TIA workup. NIHSS 1-4: Minor stroke, consider IV tPA if within window. NIHSS 5-15: Moderate stroke, IV tPA + consider thrombectomy if LVO. NIHSS 16-20: Moderate-severe. NIHSS 21-42: Severe stroke.
Evidence
Developed by Brott et al. (Stroke, 1989). Validated extensively. Required by AHA/ASA guidelines for acute stroke treatment decisions. Inter-rater reliability improved with certification training.