What is the purpose and application of the NIH (National Institutes of Health) Stroke Scale in assessing and managing acute stroke patients?

NIH Stroke Scale: Purpose and Application in Acute Stroke Management

The National Institutes of Health Stroke Scale (NIHSS) is an essential standardized assessment tool that must be administered to all acute stroke patients at presentation to quantify stroke severity, guide treatment decisions, predict outcomes, and stratify patients according to mortality risk and recovery potential. 1

Purpose of the NIHSS

The NIHSS serves several critical functions in stroke care:

• Severity assessment: Quantifies neurological impairment after stroke with scores ranging from 0-42 1
• Treatment guidance: Helps determine eligibility for acute interventions like thrombolytic therapy 2
• Outcome prediction: Strongly predicts patient recovery and mortality 2, 1
• Patient stratification: Categorizes patients by stroke severity to guide clinical decisions 2

Key Components and Administration

• 15-item neurological examination scale designed to detect virtually any stroke abnormality 2, 1
• Takes only 5-10 minutes to administer 2
• Based solely on examination without requiring historical information 2
• Can be administered at any stage by any trained clinician 2
• Original scale includes 11 items, with an additional finger extension item often added (though not contributing to total score) 2

Interpretation of NIHSS Scores

NIHSS scores provide valuable prognostic information:

• Score <6: Forecasts good recovery 2, 1
• Score <10: 60-70% of patients will have favorable outcomes at 1 year 1
• Score >16: Predicts high probability of death or severe disability 2, 1
• Score >20: Only 4-16% of patients will have favorable outcomes at 1 year 1

Clinical Applications

Recommended Assessment Timepoints

1. At time of presentation/hospital admission (within first 24 hours) 2, 1
2. At acute care discharge 2
3. Upon transfer to rehabilitation if no prior scores exist 2

Treatment Decision Support

• Helps determine eligibility for thrombolytic therapy 2, 1
• Identifies patients at higher risk of complications:
  • NIHSS ≥20: 17% risk of intracranial hemorrhage with rtPA
  • NIHSS <10: Only 3% risk of bleeding with rtPA 1

Severity Stratification

• Small stroke: Score <5 1
• Moderate stroke: Score 7-15 1
• Severe stroke: Score ≥16 1
• Critical stratification point: Scores ≤7 vs >7 show significant differences in progression risk and recovery potential 3

Training and Certification Requirements

• All professionals involved in stroke care should be trained and certified in NIHSS assessment 2, 1
• Certification involves watching training videos and passing an examination 2
• Certified examiners can be from any background (physician, nurse, therapist, social worker) 2, 1
• Inter-rater reliability between examiners for most NIHSS items is high 2, 1

Limitations and Pitfalls

• May underestimate posterior circulation stroke severity 1
• Different cutoff values are optimal for predicting outcomes in different stroke types:
  • Posterior circulation strokes: NIHSS 4
  • Anterior circulation strokes: NIHSS 8 1

Common Pitfalls to Avoid

• Including prior deficits in scoring (should be documented separately) 1
• Failing to reassess NIHSS at critical timepoints 1
• Using untrained personnel 1
• Relying solely on NIHSS without considering other clinical factors 1

Clinical Impact on Mortality and Outcomes

• Baseline NIHSS score has a profound association with mortality after acute stroke 4
• In validation studies, NIHSS score is the most important predictor of outcome, explaining 11.3-25.0% of outcome variation, compared to only 0.7-4.0% for comorbidity indices 5
• Early clinical course is highly dependent on initial stroke severity, with a notable dichotomy around an initial NIHSS score of 7 3