The NIH Stroke Scale/Score (NIHSS) is a standardized clinical assessment tool used to quantify the severity of a stroke in patients presenting with neurological symptoms. Developed by the National Institutes of Health (NIH) in the 1980s, the scale provides an objective way to evaluate and communicate neurological deficits. It is widely used in emergency departments, stroke units, and clinical trials to guide treatment decisions, monitor progress, and predict patient outcomes.
The NIHSS is particularly important in the acute evaluation of stroke because it helps determine eligibility for reperfusion therapies, such as intravenous thrombolysis and endovascular thrombectomy. It is also predictive of stroke prognosis, with higher scores indicating more severe neurological impairment and poorer outcomes.
Structure of the NIHSS
The NIHSS is composed of 11 items that assess different domains of neurological function. Each item is scored individually, and the total score ranges from 0 to 42.
| Domain | Description | Score Range |
|---|---|---|
| 1a. Level of consciousness | Alertness and responsiveness | 0–3 |
| 1b. LOC questions | Ability to answer questions correctly | 0–2 |
| 1c. LOC commands | Ability to follow simple commands | 0–2 |
| 2. Best gaze | Eye movement assessment | 0–2 |
| 3. Visual fields | Presence of hemianopia | 0–3 |
| 4. Facial palsy | Facial movement assessment | 0–3 |
| 5a. Motor arm (left) | Arm drift/weakness | 0–4 |
| 5b. Motor arm (right) | Arm drift/weakness | 0–4 |
| 6a. Motor leg (left) | Leg drift/weakness | 0–4 |
| 6b. Motor leg (right) | Leg drift/weakness | 0–4 |
| 7. Limb ataxia | Cerebellar function testing | 0–2 |
| 8. Sensory | Detection of pinprick and light touch | 0–2 |
| 9. Best language | Ability to comprehend and produce speech | 0–3 |
| 10. Dysarthria | Clarity of speech | 0–2 |
| 11. Extinction and inattention | Neglect testing with sensory and visual stimuli | 0–2 |
Interpretation
The total NIHSS score reflects stroke severity:
- 0: No stroke symptoms
- 1–4: Minor stroke
- 5–15: Moderate stroke
- 16–20: Moderate-to-severe stroke
- 21–42: Severe stroke
Higher scores generally correlate with larger infarct volumes, greater disability, and increased risk of mortality.
Clinical Significance
The NIHSS has several important clinical applications:
- Acute stroke evaluation: Helps determine eligibility for thrombolytic therapy (e.g., tPA) and mechanical thrombectomy.
- Standardized communication: Provides a common language for clinicians across specialties and institutions.
- Prognosis: Higher NIHSS scores predict worse functional outcomes and greater likelihood of dependency after stroke.
- Monitoring: Used in serial assessments to monitor progression, recovery, or complications.
- Clinical research: NIHSS is often used as an inclusion criterion and outcome measure in stroke trials.
Indications for Use
NIHSS should be administered in:
- Patients presenting with suspected acute ischemic stroke or transient ischemic attack (TIA).
- Emergency departments, stroke centers, and inpatient neurology services.
- Pre-hospital stroke evaluations in some advanced EMS systems.
- Research settings for standardization of stroke severity classification.
Limitations
Despite its value, the NIHSS has limitations:
- Bias toward anterior circulation strokes: The scale is less sensitive in detecting posterior circulation strokes.
- Language and cultural differences: Some components depend on patient language proficiency, limiting accuracy in non-native speakers.
- Limited assessment of cognitive function: NIHSS focuses mainly on motor and sensory deficits, not higher-order cognitive impairment.
- Inter-rater variability: Accuracy depends on proper training; untrained evaluators may introduce scoring errors.