How is NIHSS severity classified?

NIHSS 0: no deficit. 1–4: minor stroke. 5–15: moderate stroke. 16–20: moderate-to-severe stroke. 21–42: severe stroke. Scores >25 are associated with high mortality without early reperfusion therapy.

What NIHSS score qualifies for IV thrombolysis?

Intravenous alteplase (tPA) is indicated within 4.5 hours of ischemic stroke onset for measurable neurological deficits (typically NIHSS ≥4, though minor disabling strokes are also treated). NIHSS >25 is a relative contraindication due to increased risk of hemorrhagic transformation.

What is mechanical thrombectomy and who is eligible?

Mechanical thrombectomy (MT) involves endovascular clot retrieval for anterior circulation large vessel occlusion (LVO). Eligible criteria generally include NIHSS ≥6, pre-stroke mRS 0–1, treatment within 6 hours (extended up to 24 hours under DAWN/DEFUSE-3 imaging mismatch criteria), and confirmed LVO on vascular imaging.

NIH Stroke Scale (NIHSS) Calculator

Q: 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. Total score ranges from 0 to 42.

Q: What is the difference between NIHSS and mRS?

NIHSS measures acute neurological impairment at a specific moment in time to direct emergency reperfusion and track recovery. The modified Rankin Scale (mRS) assesses functional independence and disability in activities of daily living, typically evaluated at 90 days.

1NIHSS Stroke Severity & Prognosis

NIHSS Score	Clinical Severity Tier	Typical Neurological Deficits	Favorable Outcome (90-Day mRS 0–2)
0	No Deficit	Normal examination; consider TIA or posterior circulation territory.	~95%
1–4	Minor Stroke	Subtle motor pronator drift, isolated facial weakness, mild sensory alteration.	~80%–90%
5–15	Moderate Stroke	Hemiparesis, expressive/receptive dysphasia, hemi-inattention, facial droop.	~30%–60%
16–20	Moderate–Severe	Dense hemiplegia, forced conjugate gaze palsy, global aphasia, homonymous hemianopia.	~10%–25%
21–42	Severe Stroke	Coma or stupor, bilateral or massive hemispheric infarction, quadriplegia.	<10%

2Intravenous Thrombolysis (Alteplase / Tenecteplase)

Intravenous alteplase (0.9 mg/kg, maximum dose 90 mg; 10% bolus over 1 minute, 90% infused over 60 minutes) remains the frontline pharmacological reperfusion therapy for eligible acute ischaemic stroke patients presenting within 4.5 hours of symptom onset or last known well.

Core Eligibility Criteria (AHA/ASA 2019)

Onset strictly <4.5 hours prior to infusion initiation.
Non-contrast CT head confirms absence of intracranial hemorrhage or established massive hypoattenuation (>1/3 MCA territory).
Blood pressure strictly maintained <185/110 mmHg prior to thrombolysis and <180/105 mmHg for 24 hours post-infusion.
Platelet count ≥100,000/μL; INR ≤1.7 (if on warfarin); no full-dose therapeutic anticoagulation within 48 hours without reversal.
NIHSS Considerations: While scores ≥4 represent classic candidates, minor strokes (NIHSS 1–3) with disabling deficits (e.g., isolated severe dysphasia or visual field loss) warrant treatment. Conversely, scores >25 carry heightened hemorrhagic transformation risk.

3Endovascular Mechanical Thrombectomy (MT)

Mechanical thrombectomy has revolutionized acute management for large vessel occlusions (LVO) in the anterior circulation (distal internal carotid artery or proximal middle cerebral artery M1 segment).

Standard Window (0–6 hours): Indicated if NIHSS ≥6, pre-stroke mRS 0–1, ASPECTS score ≥6 on non-contrast CT, and confirmed proximal LVO on CT angiography.
Extended Window (6–24 hours): Indicated in selected patients meeting DAWN or DEFUSE-3 trial criteria (significant clinical-core mismatch on CT perfusion or MRI DWI-FLAIR sequences).
Bridging Therapy: Eligible patients should receive IV thrombolysis concurrently while being mobilized immediately to the catheterization lab for thrombectomy.

4NIHSS as a Serial Monitoring Instrument

In acute stroke units, NIHSS is assessed at baseline, 2 hours, 24 hours, and 7 days. A ≥4-point reduction reflects significant early neurological improvement. Conversely, a ≥4-point increase (worsening) represents an acute emergency—signaling hemorrhagic transformation, malignant cerebral edema with midline shift, or arterial re-occlusion—mandating an immediate non-contrast CT head and neurovascular consult.

5Frequently Asked Questions

What does the NIHSS measure?+

The NIHSS quantifies 11 key clinical domains: Level of Consciousness (responsiveness, questions, commands), Horizontal Gaze, Visual Fields, Facial Palsy, Motor Arm (bilateral), Motor Leg (bilateral), Limb Ataxia, Sensory loss, Language / Aphasia, Dysarthria, and Extinction / Inattention.

Can a patient have a stroke with an NIHSS of 0?+

Yes. The NIHSS is heavily weighted toward anterior circulation cortical deficits. Posterior circulation strokes (manifesting as isolated vertigo, truncal ataxia, nystagmus, or dysphagia) and lacunar infarcts with isolated sensory loss can score 0 on NIHSS despite significant clinical morbidity.

What is the difference between NIHSS and mRS?+

NIHSS measures neurological impairment in real-time during the acute phase (0–42 points). The modified Rankin Scale (mRS) measures global disability and functional dependency in daily living (0 = no symptoms, 5 = severe bedridden disability, 6 = death), typically assessed at 90 days post-stroke.

Clinical Takeaway: Rapid NIHSS calculation accelerates "door-to-needle" and "door-to-groin" times. Remember that an acute ≥4 point increase indicates neurological deterioration requiring emergent non-contrast CT imaging.

Medical Disclaimer: The NIHSS calculator is a clinical decision-support tool for trained healthcare personnel. Thrombolysis and thrombectomy decisions must be guided by vascular neuroimaging, clinical contraindication checklists, and specialist stroke team evaluation.