1NIHSS Stroke Severity Guide
| NIHSS Score | Severity | Typical Deficits | Outcome (90-day mRS 0–2) |
|---|---|---|---|
| 0 | No stroke symptoms | Normal examination | ~95% |
| 1–4 | Minor stroke | Subtle findings — sensory, mild motor, mild speech | ~80–90% |
| 5–15 | Moderate stroke | Clear motor/speech deficits, partial limb weakness | ~30–60% |
| 16–20 | Moderate–Severe | Dense hemiplegia, global aphasia, gaze deviation | ~10–25% |
| 21–42 | Severe stroke | Coma, severe neurological impairment | <10% |
tPA (Alteplase) in Acute Ischaemic Stroke
Intravenous alteplase (0.9 mg/kg, max 90 mg) remains the standard pharmacological reperfusion therapy for eligible patients with acute ischaemic stroke. Key eligibility criteria per AHA/ASA 2019 guidelines:
- Age ≥18 years; symptom onset within 3 hours (extended to 4.5 hours in selected patients per ECASS-3 criteria)
- NIHSS ≥4 (relative — low NIHSS may still benefit; high NIHSS may still be treated)
- CT head showing no haemorrhage or established large infarct (>1/3 MCA territory)
- No absolute contraindications: no prior ICH, intracranial neoplasm/AVM, active internal bleeding, recent (<3 months) head trauma/brain surgery, BP >185/110 despite treatment
Mechanical Thrombectomy Eligibility
Mechanical thrombectomy (MT) has transformed outcomes for large vessel occlusion (LVO) strokes. AHA/ASA 2018 extended MT window criteria: NIHSS ≥6, pre-stroke mRS ≤1, ASPECTS ≥6 on CT, confirmed LVO on CTA, treatment within 6 hours of onset (up to 24 hours in selected wake-up/late-window cases with favourable CT perfusion or DWI-FLAIR mismatch on MRI). NIHSS score does not independently exclude patients from MT consideration — LVO must be confirmed on vascular imaging.
NIHSS as a Serial Monitoring Tool
A reduction in NIHSS of ≥4 points from baseline is the standard definition of neurological improvement used in clinical trials (including NINDS trial). NIHSS should be performed: at baseline (admission), at 2 hours, 24 hours, 7 days, and at discharge. A worsening NIHSS of ≥4 points from baseline suggests haemorrhagic transformation, cerebral oedema, or re-occlusion — requiring urgent CT head and neurology review.
2Frequently asked questions
What does the NIHSS measure?
The NIH Stroke Scale (NIHSS) quantifies neurological deficit severity in acute stroke using 11 items: level of consciousness (3 items), gaze, visual fields, facial palsy, motor arm (both), motor leg (both), limb ataxia, sensory, language/aphasia, dysarthria, and extinction/inattention. Score 0–42. Higher scores indicate more severe deficit.
How is NIHSS severity classified?
NIHSS 0: no deficit. 1–4: minor stroke. 5–15: moderate stroke. 16–20: moderate-severe. 21–42: severe stroke. NIHSS >25 is associated with very poor outcome without reperfusion therapy. NIHSS >22 is a relative contraindication to IV thrombolysis in some guidelines due to high haemorrhagic transformation risk.
What NIHSS score qualifies for IV thrombolysis?
IV alteplase (tPA) for ischaemic stroke: onset within 4.5 hours, NIHSS ≥4 (some centres treat NIHSS 1–3 with disabling deficits), NIHSS ≤25 (relative contraindication if >25). Contraindications include haemorrhage on CT, recent surgery, anticoagulation with therapeutic INR, and prior stroke + DM combination. MRI-guided thrombolysis can extend window in wake-up strokes.
What is mechanical thrombectomy and who is eligible?
Mechanical thrombectomy (MT) removes large vessel occlusion (LVO) using catheter-based devices. Indicated for: large anterior circulation LVO (ICA, M1, M2 MCA) within 6 hours of onset (or 24 hours in DAWN/DEFUSE-3 criteria with mismatch imaging), NIHSS ≥6, and salvageable brain tissue on CT/MRI perfusion. MT is the most effective stroke treatment — NNT ~2.5 for functional independence. Available in comprehensive stroke centres in Indian metros.
How is NIHSS used for stroke prognosis?
NIHSS at 24 hours better predicts outcome than admission NIHSS. NIHSS improvement of ≥4 points at 24 hours ('early neurological improvement') predicts good 90-day outcome after thrombolysis. Discharge NIHSS 0–1 correlates with excellent functional recovery (mRS 0–1). NIHSS is also used to assess eligibility for rehabilitation services and to track recovery trajectory.
What is the difference between NIHSS and mRS?
NIHSS measures neurological deficit at a point in time — useful for acute assessment and treatment decisions. mRS (modified Rankin Scale) measures functional disability and independence — used for outcome assessment at 90 days. They measure different domains: NIHSS captures neurological findings; mRS captures functional impact on daily life. A patient can have a low NIHSS but high mRS if their deficit (e.g. isolated aphasia) severely impacts function.
Medical disclaimer: This calculator is for educational and clinical decision-support purposes only. It does not replace clinical judgment or specialist consultation. RxMedCalc is not liable for clinical decisions made solely on this tool.