NIH Stroke Scale/Score (NIHSS)
Why Use
There are nearly 800,000 cases of acute stroke in the United States every year, with 165,000 associated deaths (5th leading cause of death in Americans) ( C DC 2022 ). The NIHSS can help physicians determine the severity of a stroke, predict clinical outcomes.
When to Use
The NIHSS can help physicians quantify the severity of a stroke in the acute setting.
Formula
Pearls / Pitfalls
The National Institutes of Health Stroke Scale (NIHSS) was developed to help physicians objectively rate severity of ischemic strokes. Increasing scores indicate a more severe stroke and has been shown to correlate with the size of the infarction on both CT and MRI evaluation. NIHSS scores when assessed within the first 48 hours following a stroke have been shown to correlate with clinical outcomes at the 3-month and 1-year mark. Patients with a total score of 4 or less generally have favorable clinical outcomes and have a high likelihood of functional independence regardless of treatment. Points to keep in mind: Many guidelines and protocols warn that administering tPA in patients with a high NIHSS score (>22) is associated with increased risk of hemorrhagic conversion. These patients, however, are also the most severely debilitated and dependent from their strokes as well. Some components of the NIHSS have lower interrater reliability (i.e. facial movement, limb ataxia, neglect, level of consciousness, and dysarthria), and some may be quite limited due to altered mental status, for example. According to a 2023 study, one in three initial NIHSS scores had a clinically meaningful difference in scores between neurologists and nurses, further supporting the need for improvement in interrater reliability ( Comer et al 2023 ). A simpler, modified version of the NIHSS has been found to have greater interrater reliability with equivalent clinical performance, although it has not been as widely adopted as the original NIHSS. The patient with even a large territory posterior circulation stroke syndrome may still have a low or normal NIHSS, highlighting one of its important limitations.
Management
In patients who present with symptoms concerning for ischemic stroke: Consult Neurology. Determine the onset of stroke symptoms (or time patient last felt or was observed normal). Obtain a stat head CT to evaluate for hemorrhagic stroke. In appropriate circumstances and in consultation with both neurology and the patient, consider IV thrombolysis for ischemic strokes in patients with no contraindications. Always consider stroke mimics in the differential diagnosis, especially in cases with atypical features (age, risk factors, history, physical exam), including: Recrudescence of old stroke from metabolic or infectious stress. Todd’s paralysis after seizure. Complex migraine. Pseudoseizure, conversion disorder.
Critical Actions
The NIHSS is broadly predictive of clinical outcomes, but it is important to recognize that individual cases will vary and that management decisions must be made in consultation with the patient whenever possible. Patients with a score of <4 are highly likely to have good clinical outcomes. Whenever possible, patients with acute stroke should be transferred to a stroke center for their initial evaluation and treatment, as the holistic care (medical optimization, early initiation of PT and OT, patient and family education and discharge planning) is associated with improved clinical outcomes; some argue that most of the gains in stroke morbidity and mortality are due to these improvements in stroke care.
Advice
Consult Neurology immediately (if available) for all patients presenting with ischemic stroke. Evaluate whether the patient is a potential candidate to receive intravenous thrombolysis (tPA) . Consider further imaging including CT, CT angiography and MRI/MRA.
More Information
Language/aphasia test Dysarthria test For more information see the NIH Stroke Scale Website . See here for more information on definitions and performing the exam.