What is the role of the National Institutes of Health Stroke Scale (NIHSS) in assessing and managing acute ischemic stroke?

Role of the National Institutes of Health Stroke Scale (NIHSS) in Acute Ischemic Stroke Management

The National Institutes of Health Stroke Scale (NIHSS) is an essential standardized assessment tool that stratifies stroke severity, guides therapeutic decisions, predicts outcomes, and monitors treatment response in acute ischemic stroke management, with all professionals involved in stroke care recommended to be trained and certified in its use. 1

Clinical Utility and Decision-Making

Stratification and Treatment Selection

• NIHSS scores help stratify patients into different severity categories:

  • Small stroke: NIHSS <5
  • Moderate stroke: NIHSS 7-15
  • Severe stroke: NIHSS >16
  • Large stroke: NIHSS >20 1

• Treatment decisions are guided by NIHSS scores:

  • Patients with scores between 5-22 obtain greatest benefit from thrombolytic therapy
  • Patients with scores <10 have lower risk of intracranial hemorrhage (3%) and better outcomes (60-70% favorable at 1 year)
  • Patients with scores >22 have significantly increased risk of ICH (17%) and poor outcomes (only 4-16% favorable at 1 year), making them candidates for additional endovascular therapies 1

Prognostic Value

• NIHSS scores correlate with infarct volume and predict outcomes:

  • NIHSS <6: Good recovery
  • NIHSS ≥12 at admission: Predicts unfavorable outcomes (sensitivity: 0.51, specificity: 0.84)
  • NIHSS ≥5 at 24 hours post-thrombolysis: Better predictor of outcomes (sensitivity: 0.83, specificity: 0.65)
  • NIHSS >16: High probability of death or severe disability 1

• Recent research confirms that baseline NIHSS score has a profound association with mortality after acute stroke, helping clinicians decide on appropriate interventions 2

Monitoring Protocol

Recommended Assessment Schedule

• Complete evaluation at admission by certified personnel
• During thrombolysis:
  • Abbreviated evaluations every 15 minutes for 2 hours
  • Every 30 minutes for 6 hours
  • Every hour until 24 hours
• Immediate complete evaluation for:
  • Neurological deterioration
  • Increased abbreviated score
  • Altered level of consciousness
  • Elevated blood pressure
  • Motor exam deterioration
  • New-onset headache, nausea, or vomiting 1

Percent Change as Outcome Measure

• Percent NIHSS score change (baseline to 3 months) effectively predicts functional outcomes
• In moderate stroke (baseline NIHSS 7-15), improvement of at least 55% best predicts functional independence at 3 months 3

Limitations and Special Considerations

Posterior Circulation Strokes

• NIHSS may underestimate severity of posterior circulation strokes
• Symptoms like vertigo or difficulty swallowing are not included in standard NIHSS evaluation
• No standardized system for evaluating posterior circulation strokes is currently available 1
• The expanded NIHSS (e-NIHSS) has been proposed to better assess posterior circulation strokes by adding specific elements to existing items, showing approximately 2 points higher scores in posterior circulation infarcts compared to classical NIHSS 4

Mild Strokes

• Patients with mild strokes (NIHSS ≤4) still have a 54% chance of visible arterial occlusion
• These patients have a 77% chance of excellent outcomes (mRS ≤1 at 3 months) with thrombolysis
• Risk of hemorrhagic transformation is only 5% 1

Implementation and Common Pitfalls

Implementation Challenges

• Successful implementation requires staff education, emphasis during interdisciplinary rounds, and use of pocket reference cards
• One study showed NIHSS assessment increased from 12% to 69% after targeted quality improvement initiatives 5

Common Pitfalls

1. Including prior deficits in scoring
2. Underestimating posterior circulation strokes
3. Failing to reassess NIHSS at critical timepoints
4. Using untrained personnel
5. Relying solely on NIHSS without considering other clinical factors 1

Emerging Concerns

• Despite being in use for over 30 years, the NIHSS has limitations in capturing all complex effects of stroke
• Recent literature suggests the need for an updated, more comprehensive clinical stroke severity rating scale 6

Clinical Integration

• All professionals involved in stroke care should be trained and certified in NIHSS assessment
• NIHSS scores should be documented at time of transfer to rehabilitation settings
• Early rehabilitation assessment is particularly important for patients with high NIHSS scores
• NIHSS should be used alongside other clinical factors for comprehensive stroke management 1