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.