What is the NIHSS?
The National Institutes of Health Stroke Scale (NIHSS) is a standardized neurological examination tool used by healthcare providers to objectively quantify the severity of stroke symptoms. Developed in 1989 by researchers at the NIH, it has become the gold standard for assessing stroke patients in emergency departments, clinical trials, and stroke units worldwide.
The NIHSS evaluates 11 categories of neurological function including consciousness, eye movements, visual fields, facial movement, limb strength, coordination, sensation, language, speech, and neglect. Each item is scored on an ordinal scale with 0 representing normal function. The total score ranges from 0 to 42, with higher scores indicating more severe neurological deficits.
The scale can be administered in less than 10 minutes by a trained examiner and has demonstrated good inter-rater reliability. It serves as both a clinical assessment tool and a communication instrument, allowing healthcare teams to objectively track neurological changes over time.
Scoring System
Each of the 15 items is scored independently. The examiner should score what the patient does, not what the examiner thinks the patient can do. Items are not weighted differently; the total score is a simple sum.
| Item | Assessment | Score Range |
|---|---|---|
| 1a | Level of Consciousness | 0–3 |
| 1b | LOC Questions (month, age) | 0–2 |
| 1c | LOC Commands (open/close eyes, grip/release) | 0–2 |
| 2 | Best Gaze (horizontal eye movement) | 0–2 |
| 3 | Visual Fields | 0–3 |
| 4 | Facial Palsy | 0–3 |
| 5a/5b | Motor Arm (left/right) | 0–4 each |
| 6a/6b | Motor Leg (left/right) | 0–4 each |
| 7 | Limb Ataxia | 0–2 |
| 8 | Sensory | 0–2 |
| 9 | Best Language | 0–3 |
| 10 | Dysarthria | 0–2 |
| 11 | Extinction / Inattention | 0–2 |
Score Interpretation
| Total Score | Stroke Severity | Clinical Significance |
|---|---|---|
| 0 | No stroke symptoms | Normal neurological exam |
| 1–4 | Minor stroke | Minor deficits; may not require aggressive treatment |
| 5–15 | Moderate stroke | Significant deficits; strong candidate for thrombolysis |
| 16–20 | Moderate to severe stroke | Major deficits; higher risk of hemorrhagic transformation |
| 21–42 | Severe stroke | Severe deficits; poor prognosis; high mortality risk |
NIHSS Components Diagram
tPA Eligibility & the NIHSS
Tissue plasminogen activator (tPA, alteplase) is the primary thrombolytic therapy for acute ischemic stroke. The NIHSS score is a critical factor in determining eligibility for tPA administration:
- NIHSS < 5: Generally considered too mild for thrombolysis. The risks of bleeding may outweigh the benefits. However, disabling symptoms (e.g., isolated aphasia or hemianopia) may still warrant treatment regardless of low total score.
- NIHSS 5–25: The primary target range for tPA therapy. These patients have meaningful deficits that are likely to benefit from thrombolytic treatment.
- NIHSS > 25: Very severe strokes with higher risk of hemorrhagic transformation. Treatment decisions should be individualized, considering the risk-benefit ratio.
The standard treatment window for IV tPA is within 4.5 hours of symptom onset. Mechanical thrombectomy may extend the treatment window to 24 hours for large vessel occlusions in selected patients, as demonstrated by the DAWN and DEFUSE 3 trials.
Stroke Types
Ischemic Stroke (87% of all strokes)
Caused by a blood clot blocking blood flow to the brain. Subtypes include thrombotic (clot forms in a brain artery), embolic (clot travels from elsewhere), and lacunar (small vessel disease). Ischemic strokes are the primary indication for tPA and mechanical thrombectomy.
Hemorrhagic Stroke (13% of all strokes)
Caused by bleeding into or around the brain. Includes intracerebral hemorrhage (bleeding within the brain tissue) and subarachnoid hemorrhage (bleeding in the space surrounding the brain). Hemorrhagic strokes are a contraindication for tPA. The NIHSS can still be used for severity assessment, though it was primarily designed for ischemic stroke.
Transient Ischemic Attack (TIA)
Often called a "mini-stroke," a TIA produces temporary neurological symptoms that resolve completely within 24 hours. TIAs are a warning sign for future stroke. Patients with TIA typically have an NIHSS of 0 at the time of examination. The ABCD2 score is often used instead for TIA risk stratification.
Worked Example
A 68-year-old patient presents to the emergency department with sudden onset right-sided weakness and difficulty speaking, 2 hours after symptom onset:
| Item | Finding | Score |
|---|---|---|
| 1a. Consciousness | Alert | 0 |
| 1b. LOC Questions | Answers one correctly | 1 |
| 1c. LOC Commands | Performs both correctly | 0 |
| 2. Best Gaze | Partial gaze palsy | 1 |
| 3. Visual | No visual loss | 0 |
| 4. Facial Palsy | Partial paralysis (lower face) | 2 |
| 5a. Motor Arm Left | No drift | 0 |
| 5b. Motor Arm Right | Drift before 10 seconds | 1 |
| 6a. Motor Leg Left | No drift | 0 |
| 6b. Motor Leg Right | Some effort against gravity | 2 |
| 7. Limb Ataxia | Absent | 0 |
| 8. Sensory | Mild-to-moderate loss | 1 |
| 9. Best Language | Mild-to-moderate aphasia | 1 |
| 10. Dysarthria | Mild-to-moderate | 1 |
| 11. Extinction | No abnormality | 0 |
With a score of 10 and symptom onset 2 hours ago, this patient is a strong candidate for IV tPA (alteplase). The score falls within the 5–25 range where thrombolytic therapy has the greatest net benefit.
Frequently Asked Questions
Who can administer the NIHSS?
The NIHSS should be administered by healthcare professionals who have received certification training. This typically includes physicians, nurses, paramedics, and other allied health professionals. Certification courses are available through the American Heart Association and online platforms.
How often should the NIHSS be repeated?
In acute stroke management, the NIHSS is typically assessed at presentation, at 2 hours post-tPA, at 24 hours, and at discharge. More frequent assessments may be needed if the patient's condition changes. Serial NIHSS scores help track neurological improvement or deterioration.
Can the NIHSS predict long-term outcomes?
Yes, the initial NIHSS score is a strong predictor of long-term outcomes. A baseline score greater than 16 is associated with a high probability of death or severe disability, while a score less than 6 is associated with good recovery. However, individual outcomes vary and the NIHSS should be considered alongside other clinical factors.
What are the limitations of the NIHSS?
The NIHSS has been criticized for being weighted toward anterior circulation strokes (particularly left hemisphere). Posterior circulation strokes involving the brainstem and cerebellum may present with significant deficits (vertigo, ataxia, cranial nerve palsies) that receive relatively low NIHSS scores. Additionally, the scale does not directly assess cognitive function, mood, or quality of life.