The National Institutes of Health Stroke Scale, or NIHSS, is a standardized assessment tool used globally by medical professionals to objectively measure the severity of neurological deficits caused by a stroke. Developed initially for clinical research, the NIHSS ensures consistent data collection and has since become the standard clinical method for evaluating stroke severity. This allows for a common language among all healthcare providers involved in a patient’s care.
The Critical Role in Acute Stroke Care
The NIHSS is primarily used in the hyperacute phase of stroke management, often starting in the ambulance or upon arrival in the Emergency Department. This rapid assessment is crucial because time is a limiting factor for effective stroke treatments. The scale is designed for systematic evaluation, typically completed in under ten minutes by trained personnel.
The standardization of the NIHSS ensures the initial evaluation is reproducible, meaning different assessors should arrive at the same score for the same patient. This good inter-rater reliability is foundational for triage and treatment pathways. The scale also serves as a baseline measure against which a patient’s progress or decline can be tracked. Repeated scoring helps the medical team monitor the effectiveness of interventions and adjust the plan of care.
Step-by-Step Assessment Components
The NIHSS comprises eleven specific items, which are grouped into domains that assess key neurological functions. The assessment begins by determining the patient’s level of consciousness (LOC) and orientation, requiring the patient to state the current month and their age. The examiner then proceeds to test the patient’s ability to follow simple commands, such as opening and closing their eyes and gripping the examiner’s non-paretic hand.
The next domain evaluates visual and ocular movements, starting with the Best Gaze item, which focuses solely on horizontal eye movements. The patient is asked to follow a target side-to-side without moving their head. The examiner observes for any forced deviation or inability to track laterally. Visual fields are tested by confrontation, where the examiner wiggles fingers in the patient’s peripheral vision, checking the upper and lower quadrants on both sides.
Motor function is one of the most heavily weighted domains, testing the strength and endurance of the upper and lower limbs. For the arms, the patient holds each arm, palm down, at a 90-degree or 45-degree angle for ten seconds against gravity. Leg strength is similarly assessed by asking the patient to hold each leg up at a 30-degree angle for five seconds while lying down. The score reflects the degree to which the limb drifts or falls during the designated time.
Coordination is checked by the Limb Ataxia component, requiring the patient to perform the finger-to-nose and heel-to-shin tests. This item is scored only if any incoordination is clearly out of proportion to any existing weakness. The Sensory item assesses feeling using a pinprick, comparing the sensation on the patient’s face, arms, and legs.
The final functional domains focus on communication and awareness. The Best Language item assesses comprehension and expression by asking the patient to describe a picture, name objects, and read a list of sentences. The Dysarthria item specifically evaluates the clarity of speech, not the content of the language itself, by having the patient repeat a list of words. The assessment concludes with Extinction and Inattention, which checks for neglect by using double simultaneous stimulation.
Scoring Methodology and Severity Levels
Each of the eleven components of the NIHSS is assigned an individual score, typically ranging from 0 to 4. A score of 0 indicates normal function, and a higher score signifies a greater degree of impairment. For instance, the motor items, which are tested bilaterally, are scored from 0 (no drift) to 4 (no movement). Other items like Best Gaze and Dysarthria use a smaller scale, often 0 to 2 or 0 to 3.
The individual scores from all components are summed to produce a single total NIHSS score, which can range from a minimum of 0 to a maximum of 42. This final number is then used to classify the overall severity of the stroke. A score of 0 indicates no stroke symptoms, while a score between 1 and 4 is typically defined as a minor stroke.
A score ranging from 5 to 15 is categorized as a moderate stroke. Scores between 16 and 20 indicate a moderate to severe stroke, often suggesting a higher risk of poor outcomes. The highest scores, from 21 to 42, represent a severe stroke, correlating with profound impairment and large areas of brain injury.
How the Score Guides Treatment Decisions
The final NIHSS score is a primary factor in determining a patient’s eligibility for time-sensitive, acute stroke interventions. For patients with an acute ischemic stroke, the score helps weigh the potential benefit of clot-busting medication, such as intravenous thrombolysis (tPA), against the risk of serious complications like intracranial hemorrhage. Patients with very minor strokes, typically an NIHSS score of less than 5, are often excluded from tPA treatment, as the risk of bleeding may outweigh the small functional gain.
Conversely, a high NIHSS score, sometimes exceeding 25, can lead to exclusion from tPA, suggesting a large area of brain injury where the risk of hemorrhage is elevated. The score is also an important factor for determining eligibility for mechanical thrombectomy, a procedure to physically remove a large blood clot. Guidelines for thrombectomy often require an NIHSS score of 6 or greater, in addition to favorable imaging and specific time window requirements. The NIHSS score guides the medical team in rapid, evidence-based decisions regarding the most appropriate treatment pathway.