NIH Stroke Scale (NIHSS) Calculator

About

The National Institutes of Health Stroke Scale (NIHSS) was originally developed by Brott, Adams, and colleagues in 1989 as a research tool to standardize the measurement of neurological deficit severity in acute stroke clinical trials. It was later refined by Lyden et al. in 1994 and has since evolved into the standard clinical instrument for acute stroke assessment worldwide. The full NIHSS comprises 15 items evaluating level of consciousness, gaze, visual fields, facial palsy, motor arm and leg function, limb ataxia, sensory function, language, dysarthria, and extinction/inattention. This simplified version includes 11 core items, grouping motor arm and leg scores by combining both sides. Each item is graded on an ordinal scale from 0 (normal) to 2, 3, or 4 (most severe), with the motor components allowing up to 8 points when both sides are affected. Total scores range from 0 (no deficit) to 42 (most severe deficit). The NIHSS has been extensively validated across diverse populations and is used in all major stroke trials as the standard outcome measure. It shows high inter-rater reliability after formal certification and is sensitive to clinically meaningful changes in neurological status. The scale is endorsed by the American Heart Association/American Stroke Association (AHA/ASA), the European Stroke Organisation, and the World Stroke Organization. The NIHSS is fundamental to treatment decisions — it identifies candidates for intravenous thrombolysis and endovascular thrombectomy and tracks neurological improvement or deterioration during hospitalization.

Formula

NIHSS = LOC (0-3) + Gaze (0-2) + Visual (0-3) + Facial Palsy (0-3) + Motor Arm (0-8) + Motor Leg (0-8) + Ataxia (0-2) + Sensory (0-2) + Language (0-3) + Dysarthria (0-2) + Extinction (0-2)

The NIHSS is calculated by summing the scores from all assessed items, each representing a distinct neurological domain. Level of consciousness (0-3) assesses overall alertness: 0 for alert, 1 for drowsy but arousable, 2 for obtunded requiring repeated stimulation, and 3 for coma with no response. Gaze (0-2) evaluates horizontal eye movement: 0 for normal, 1 for partial gaze palsy, and 2 for forced deviation or total palsy. Visual fields (0-3) test each quadrant: 0 for no loss, 1 for partial hemianopia, 2 for complete hemianopia, and 3 for bilateral hemianopia or cortical blindness. Facial palsy (0-3) assesses lower and upper face weakness: 0 for normal, 1 for minor asymmetry, 2 for partial lower face weakness, and 3 for complete unilateral or bilateral paralysis. Motor arm (0-8) combines both arms: tested with arms held at 45° (supine) or 90° (sitting) for 10 seconds — drift in one arm scores 2, drift in both scores 4, some effort scores 6, and no effort scores 8. Motor leg (0-8) similarly combines both legs with the leg held at 30° for 5 seconds. Limb ataxia (0-2) tests finger-to-nose and heel-to-shin for cerebellar dysfunction. Sensory (0-2) evaluates pinprick sensation on the face, arm, trunk, and leg. Language (0-3) assesses naming, fluency, and comprehension through picture description and object naming. Dysarthria (0-2) evaluates speech articulation clarity. Extinction/inattention (0-2) tests simultaneous bilateral stimulation. Each item contributes incrementally to a maximum total of 42 points. In general, scores of 0-4 indicate minor stroke, 5-15 moderate stroke, 16-20 moderate-severe stroke, and 21-42 severe stroke. Serial NIHSS assessments are critical: a decrease of 4 or more points indicates significant improvement, while an increase of 4 or more points signals neurological deterioration.

Score Interpretation

The NIHSS is the reference standard for acute stroke assessment and is incorporated into all major stroke treatment guidelines, including the American Heart Association/American Stroke Association (AHA/ASA) 2019 Guidelines for the Early Management of Acute Ischemic Stroke and the European Stroke Organisation (ESO) guidelines. The baseline NIHSS score at presentation is the single strongest predictor of 90-day functional outcome, with a score of 0-4 predicting good recovery in over 80% of patients, while scores above 15 predict poor functional outcomes. The NIHSS guides critical treatment decisions: patients with NIHSS ≥ 4 are generally considered candidates for intravenous thrombolysis with alteplase within 4.5 hours of symptom onset, though some guidelines also consider patients with NIHSS < 4 who have disabling deficits. Patients with NIHSS ≥ 6 and evidence of large vessel occlusion on CT angiography are typically candidates for mechanical thrombectomy, particularly if within 6 hours of onset, extended to 24 hours with advanced perfusion imaging (DAWN and DEFUSE-3 criteria). Serial NIHSS assessments during the first 24 hours are highly prognostic: improvement of 4 or more points correlates with recanalization, while worsening signals hemorrhagic transformation, edema progression, or reocclusion. The NIHSS is also used as a stratification tool in clinical trials, as a measure of stroke severity for hospital benchmarking, and to identify patients needing ICU-level monitoring. However, the NIHSS has limitations: it is heavily weighted toward left hemisphere functions (language), underestimates posterior circulation stroke severity, and is less sensitive for mild or right hemisphere deficits. The modified NIHSS (mNIHSS) and shortened versions address some of these limitations.

Reference Ranges