The National Institutes of Health Stroke Scale (NIHSS) is a standardized, rapid assessment tool used by medical professionals to quantify the severity of a stroke. This scale provides a systematic, consistent method for measuring the neurological deficit a patient is experiencing. The NIHSS score ranges from 0, indicating no neurological deficit, up to a maximum of 42, which signifies a very severe stroke. Quantifying the impairment helps guide treatment decisions, track changes in a patient’s condition, and facilitate clear communication among the care team.
Assessing Alertness and Mental Status
The NIHSS begins by evaluating the patient’s level of consciousness (LOC) and basic cognitive function. This initial assessment determines how awake and responsive the patient is. The scoring for LOC ranges from 0 (fully alert and responsive) to 3 (totally unresponsive, showing only reflex movements or none).
Beyond wakefulness, the examiner tests orientation by asking two specific questions: the current month and the patient’s age. Answering both correctly earns a score of 0, while incorrect answers increase the score, reflecting impaired cognitive function. This section also assesses the ability to follow simple motor commands, such as opening and closing the eyes, and making and releasing a fist.
Evaluating Communication and Cranial Nerve Function
This section assesses functions controlled by the cranial nerves, including the eyes, face, and speech. The examination begins with the Best Gaze, checking the patient’s ability to move their eyes horizontally and looking for any forced deviation. A score of 0 indicates normal eye movement, but a score of 1 is given if the patient has a partial gaze palsy.
The Visual Fields test checks for peripheral vision loss (hemianopia) using a confrontation technique. The Facial Palsy assessment checks for symmetry in facial muscle movement by asking the patient to show their teeth or squeeze their eyes shut. Drooping of the face suggests weakness caused by the stroke.
The assessment of Best Language evaluates the cognitive content of speech, including comprehension and naming objects, to gauge the extent of aphasia (difficulty with language). Separately, the Dysarthria component focuses on the clarity of articulation (slurred speech). Dysarthria is a motor problem affecting speech muscles, while aphasia is a cognitive problem related to language processing.
Measuring Physical Strength and Coordination
The NIHSS dedicates significant focus to motor function, which is often the most visible sign of a stroke. Motor Arm and Motor Leg strength are assessed using the “drift” test, where the patient holds their limbs up against gravity for a specific period (10 seconds for arms; 5 seconds for legs). The examiner observes the limb for downward drift, which indicates weakness, and scores severity from 0 (no drift) to 4 (no movement). This testing is conducted separately for each of the four limbs, providing a detailed, lateralized measure of muscle strength.
Limb Ataxia checks for coordination problems, which are often indicative of damage to the cerebellum. The patient performs the finger-to-nose test and the heel-to-shin test, and the examiner scores any lack of coordination or tremor that is out of proportion to any existing weakness. The final element in this physical assessment is the Sensory test, which checks the patient’s ability to feel a pinprick or light touch on the face, arms, and legs. Sensation is scored as normal, mildly decreased, or severely decreased, with a score of 2 indicating a total loss of feeling.
Identifying Neglect and Higher Brain Function
The final item on the NIHSS assesses for Extinction and Inattention, a phenomenon commonly known as neglect. This test is designed to uncover a higher-order perceptual deficit rather than a simple motor or sensory loss. Neglect is the failure to recognize or respond to stimuli on one side of the body or visual field, even when the basic sensory input on that side is intact.
The examiner performs double simultaneous stimulation, touching the patient on both sides of the body at the same time or presenting visual stimuli simultaneously. If the patient fails to notice the stimulus on the side opposite the brain injury, it suggests damage to the parietal lobe. The score reflects whether the patient ignores one side of space, which significantly impacts long-term functional recovery.