Neurology
NIHSS (Stroke Severity)
National Institutes of Health Stroke Scale.
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Background
The National Institutes of Health Stroke Scale (NIHSS) is a standardised 15-item neurological examination that quantifies the severity of an acute stroke. It scores level of consciousness, gaze, visual fields, facial and limb motor function, ataxia, sensation, language, dysarthria and extinction/inattention, giving a total from 0 to 42. Higher totals reflect more neurological deficit, and the pattern of deficits also hints at the vascular territory involved. It is performed at presentation and repeated to track deterioration or improvement.
Interpreting the result
A total of 0–4 indicates a minor stroke, 5–15 a moderate stroke, 16–20 a moderate-to-severe stroke and 21–42 a severe stroke. The score is used alongside imaging and the time from onset to inform reperfusion decisions: very low scores may not warrant the risks of thrombolysis while very high scores can carry a higher bleeding risk, and large-vessel occlusion (often with higher scores) raises the question of thrombectomy. A rising score over time signals clinical deterioration and prompts urgent reassessment.
Advice
Higher scores indicate more severe stroke and inform thrombolysis/thrombectomy decisions alongside imaging and time windows. Follow local stroke pathways.
Worked example
A patient presents with drowsiness (1a +1), a forced gaze deviation (+2), complete hemianopia (+2), partial facial palsy (+2), no movement in the right arm (+4) and right leg (+3), severe sensory loss (+2) and global aphasia (+3), totalling 19. This is a moderate-to-severe stroke, likely a large-vessel occlusion, prompting urgent imaging and consideration of reperfusion therapy within the local pathway.
Pearls / pitfalls
- It under-weights posterior-circulation and right-hemisphere strokes — a disabling brainstem or cerebellar stroke can produce a deceptively low NIHSS.
- Aphasia and reduced consciousness can inflate the score by making several items difficult to test; score what you observe using the standard rules.
- A low score does not mean a benign stroke: an isolated hemianopia or hand weakness may score little yet be very disabling.
- Consistency matters more than perfection — use the standardised instructions and, ideally, NIHSS-certified assessors to make serial scores comparable.
Evidence & validation
The scale was developed by Brott and colleagues in 1989 and has since been extensively validated for reliability and as a predictor of outcome and treatment response. It is embedded in international and UK stroke guidelines and reperfusion trial protocols as the standard measure of stroke severity.
Frequently asked questions
What NIHSS score counts as a severe stroke?
A total of 21 or more is classed as severe, 16–20 as moderate-to-severe, 5–15 as moderate and 0–4 as minor. The bands guide severity but always sit alongside imaging and the clinical picture.
Can a low NIHSS still be a serious stroke?
Yes. The scale under-detects posterior-circulation strokes and some deficits, so a low score can accompany a disabling or life-threatening stroke. Clinical judgement and imaging remain essential.
Does the NIHSS decide whether to give thrombolysis?
No single number decides it. The score helps weigh likely benefit against bleeding risk, but the decision also depends on time from onset, imaging and contraindications within the local pathway.
How often should the NIHSS be repeated?
It is repeated to monitor for deterioration or recovery — for example after reperfusion treatment or if the patient changes clinically. A rising score should trigger urgent reassessment.
Who should perform the NIHSS?
Ideally a trained, certified assessor following the standard instructions, so that serial scores by different staff remain comparable. Free certification is widely available.
References
- Brott T, Adams HP, Olinger CP, et al. Measurements of acute cerebral infarction: a clinical examination scale. Stroke. 1989;20(7):864–870.
- NICE NG128: Stroke and transient ischaemic attack in over 16s: diagnosis and initial management. 2019.
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