NIH Stroke Scale (NIHSS)
Standardized 15-item assessment of ischemic stroke severity. Total range 0–42.
About this calculator
The NIHSS (National Institutes of Health Stroke Scale) is the standard for stroke severity assessment. Developed by Brott et al. (Stroke, 1989), revised 1994. Fifteen items: level of consciousness, gaze, visual fields, facial palsy, limb strength, ataxia, sensation, speech, dysarthria, neglect. Sum 0-42. Severity interpretation. 0 – no deficit. 1-4 – minor stroke. 5-15 – moderate. 16-20 – moderate-severe. 21-42 – severe. Clinical use. Standardized assessment in stroke centers. Thrombolysis decision with alteplase – NIHSS 4-25 within 4.5 hours of symptom onset (AHA/ASA 2019), with caution at NIHSS >25 (hemorrhagic transformation risk). NIHSS >=6 in the first 24 hours after anterior circulation ischemic stroke – criterion for endovascular thrombectomy in the up-to-24-hour window (DAWN, DEFUSE-3). Prognosis. Each additional admission NIHSS point raises the risk of poor functional outcome (mRS 3-6) by 24%. NIHSS 0-5 – >80% chance of functional independence at 90 days; NIHSS >20 – <30%. NIHSS is tracked every 4-6 hours in the first 24 hours, then daily. Limitations. Overestimates deficit in left-sided strokes (dominant hemisphere) due to aphasia, underestimates right-sided (less neglect captured). Does not fully assess cerebellar and brainstem function – some posterior circulation patients have NIHSS=0 with severe deficits (e.g., isolated truncal ataxia, Wallenberg syndrome). In patients with prior neurologic deficit NIHSS is hard to interpret – baseline mRS is needed.
Source
Formula version: brott-1989-aha-2019-v1
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