The National Institutes of Health Stroke Scale (NIHSS) is a standardized neurological assessment tool used primarily in acute stroke settings. This brief examination provides a quantitative measure of neurological deficits caused by a stroke. It helps guide immediate medical decisions and offers a consistent, objective score of stroke severity. This article serves as a practical guide on how to administer the NIHSS assessment.
Understanding the Scale’s Purpose and Structure
The NIHSS establishes a baseline severity score, which is fundamental for stroke management and research. This initial score determines a patient’s eligibility for time-sensitive treatments, such as intravenous tissue plasminogen activator (tPA) or mechanical thrombectomy. Tracking the score over time allows clinicians to monitor the patient’s neurological status for improvement or deterioration.
The scale is composed of 11 components that assess various aspects of brain function, including consciousness, vision, motor strength, sensation, coordination, and language. A score of 0 on any item indicates normal function, while higher scores reflect greater impairment. The total NIHSS score ranges from 0 (no deficit) to a maximum of 42 (most severe deficit).
Proper administration requires a standardized environment and specific training to ensure reliable results between different examiners. The assessment must be performed sequentially, as the patient’s initial level of consciousness dictates the ability to test subsequent items. Scoring is based strictly on what the patient does during the test, not on the examiner’s belief of the patient’s capabilities.
Step-by-Step Administration of the NIHSS Components
Level of Consciousness (LOC)
The first three items assess the patient’s level of consciousness (LOC), which influences the scoring of later components. Item 1a, LOC, is scored based on responsiveness, ranging from alert (0) to requiring repeated or painful stimulation (2), or being totally unresponsive (3). Item 1b, LOC Questions, requires the patient to correctly state the current month and their age; only fully correct answers receive a score of 0.
Item 1c, LOC Commands, tests the ability to follow a two-step command, such as asking the patient to open and close their eyes, and then grip and release the non-paretic hand. The examiner may use pantomime to demonstrate the task, but must not coach the patient. Scoring is based on the number of tasks performed correctly, with 0 for both and 2 for neither.
Cranial Nerves and Visual Function
The Best Gaze (Item 2) assessment focuses only on horizontal eye movements. The patient follows a target object from side to side without moving their head. If eye deviation can be overcome by voluntary effort or the oculocephalic reflex, a score of 1 is assigned. A forced deviation that cannot be overcome scores 2.
Visual Fields (Item 3) are tested by confrontation, examining the upper and lower quadrants of both eyes. The examiner may use finger counting or a visual threat maneuver to check for hemianopia. Facial Palsy (Item 4) is assessed by asking the patient to show their teeth, raise their eyebrows, and close their eyes tightly. Symmetry of the grimace is observed, with scores ranging from 0 (normal movement) to 3 (complete paralysis of one or both sides).
Motor Function and Coordination
Motor Arm (Item 5) and Motor Leg (Item 6) are detailed components tested separately for the left and right sides. For the arm, the patient extends the limb (palm down) for 10 seconds—at 90 degrees if sitting or 45 degrees if supine. Any downward drift before 10 seconds indicates a deficit. Scores reflect the level of weakness, ranging from slight drift (1) to no movement (4).
The leg is tested while the patient is supine, holding the leg at 30 degrees for 5 seconds. A drift before 5 seconds is an abnormal finding and is scored similarly to the arm motor function. Limb Ataxia (Item 7) uses the finger-to-nose and heel-to-shin tests on both sides to find evidence of a cerebellar lesion. Ataxia is only scored if the clumsiness is out of proportion to any coexisting motor weakness.
Sensory and Language Items
Sensory (Item 8) function is tested by comparing the patient’s sensation to a pinprick on the face, arms, and legs. Only sensory loss clearly attributable to the stroke is scored as abnormal, with a score of 2 reserved for severe or total loss. Best Language (Item 9) is assessed by asking the patient to describe a standardized picture, name objects, and read a list of sentences. The score reflects the patient’s overall language ability.
Dysarthria (Item 10) evaluates the clarity of the patient’s speech, separate from language comprehension or fluency. The patient repeats a list of specific words, and the score reflects the degree of slurring, from mild (1) to unintelligible or mute (2). Extinction and Inattention (Item 11), formerly known as neglect, is the final component. This is tested through double simultaneous stimulation, using visual and tactile stimuli. The goal is to see if the patient fails to perceive a stimulus on one side when both sides are stimulated simultaneously.
Calculating the Total Score
The total NIHSS score is the summation of the scores from all 11 categories. Since each component is an ordinal scale, the final number provides a quick and objective measure of overall stroke impairment. The maximum possible score is 42, indicating a profound neurological deficit.
Interpreting the total score provides a general guide to stroke severity.
Stroke Severity Interpretation
- A score of 0 to 4 is considered a minor stroke.
- A score between 5 and 15 indicates a moderate stroke.
- Scores ranging from 16 to 20 suggest a moderate-to-severe stroke.
- A score of 21 or higher is consistent with a severe stroke.
Applying the Results and Ensuring Consistency
The NIHSS score is a foundational element in acute stroke care, directly influencing time-sensitive treatment decisions. Patients with scores indicating a moderate to severe deficit are often prioritized for therapies like intravenous thrombolysis or endovascular thrombectomy. The score provides a standardized language for healthcare providers to communicate a patient’s neurological status, which is important during patient transfers and handoffs.
Scoring variability can occur due to factors like patient fatigue, pre-existing conditions, or lack of examiner experience. For instance, pre-existing blindness or intubation must be accounted for by assigning specific default scores or using alternative testing methods. To ensure consistency and high inter-rater reliability (agreement between different examiners), specialized training and certification programs are necessary. This approach minimizes discrepancies in scoring, ensuring the NIHSS remains a reliable tool for monitoring neurological status and confirming treatment efficacy.