NIHSS: National Institutes of Health Stroke Scale

The NINDS rt-PA trial (1995) included patients with NIHSS 4-25; current guidelines recommend considering IV tPA for NIHSS 4-25 (some centers extend to NIHSS 0-3 in selected cases). NIHSS <4 indicates minor stroke with 90-day disability rate <15% without thrombolysis; thrombolytic benefit marginal and risk of hemorrhage may outweigh benefit. Conversely, NIHSS >25 indicates severe stroke; thrombolytic benefit is modest and hemorrhage risk elevated. Always integrate NIHSS with clinical judgment, time-from-symptom-onset, imaging, and patient factors.

Yes, paramedics and nurses can administer NIHSS after formal video certification training (typically 30-60 minutes). However, inter-rater reliability is highest among physicians and trained stroke coordinators. Studies show paramedic NIHSS scores differ from physician assessment by ±2-3 points on average. Use certified paramedic NIHSS in prehospital settings to trigger stroke alert and direct transport to comprehensive stroke centers; confirm with physician NIHSS in ED. Do not make treatment decisions based on uncertified assessment.

Posterior circulation strokes (vertebrobasilar distribution) affecting brainstem, cerebellum, and thalamus commonly present with vertigo, ataxia, facial weakness, and dysarthria—areas emphasized in NIHSS. However, NIHSS consciousness and language items are cortical; purely cerebellar strokes (ataxia, nausea, dysmetria, normal consciousness) may score low NIHSS (5-10) despite significant disability. The scale is more sensitive to anterior circulation (carotid) stroke. Clinical suspicion for posterior stroke should persist despite low NIHSS; MRI diffusion imaging is gold standard.

In motor strength testing, the clinician observes for antigravity weakness without full strength loss. An arm held at 90° shoulder abduction/elbow extension for 10 seconds without downward drift scores 0; slow downward drift within 10 seconds scores 1; unable to sustain against gravity scores 2; unable to move against gravity scores 3; no movement scores 4. 'Drift' indicates mild-moderate weakness; it is the most commonly detected motor abnormality in mild stroke (NIHSS 1-5) and distinguishes true paresis from normal variation in strength.

NIHSS is valid descriptively in hemorrhagic stroke (intracerebral or subarachnoid hemorrhage); it quantifies acute neurological deficit and predicts outcome. However, treatment decisions differ fundamentally from ischemic stroke: thrombolytics are contraindicated in hemorrhage. NIHSS score alone cannot distinguish ischemic from hemorrhagic stroke; CT head (non-contrast) is mandatory to differentiate. In ICH, NIHSS correlates with hematoma volume and predicts 30-day mortality; higher baseline NIHSS indicates worse prognosis.