Should prior deficits be included when calculating the National Institutes of Health (NIH) scale?

Including Prior Deficits in NIH Stroke Scale Calculation

Prior deficits should NOT be included when calculating the NIH Stroke Scale (NIHSS) score, as the scale is designed to measure the current stroke severity, not pre-existing neurological deficits. 1

Purpose and Design of the NIHSS

The NIHSS is a standardized, validated instrument specifically designed to:

• Assess severity of neurological impairment after stroke
• Stratify patients according to stroke severity
• Predict likely outcomes
• Guide decisions about acute stroke therapy (such as thrombolytic therapy)

The scale focuses on measuring the current neurological status resulting from the acute stroke event, not pre-existing conditions.

Proper Administration Guidelines

• Timing: The NIHSS should be administered at:

  • Time of presentation/hospital admission, or at least within first 24 hours 1
  • At the time of acute care discharge 1
  • When transferred to rehabilitation if no prior scores exist 1

• Scoring Focus: The NIHSS score should reflect only the current deficits from the acute stroke 2

  • A score >16 forecasts high probability of death or severe disability
  • A score <6 forecasts good recovery

Rationale for Excluding Prior Deficits

1. Measurement Accuracy: Including prior deficits would inflate the score and misrepresent the severity of the current stroke event 1

2. Treatment Decisions: NIHSS scores influence acute treatment decisions such as thrombolytic therapy eligibility; including prior deficits could lead to inappropriate treatment decisions 1, 2

3. Outcome Prediction: The scale's predictive value for patient recovery is based on measuring only the current stroke's impact 1

Common Pitfalls to Avoid

• Misattribution Error: Attributing chronic deficits to the acute stroke, resulting in inappropriately high scores 2

• Inconsistent Scoring: Different examiners may interpret prior deficits differently, reducing inter-rater reliability 1, 3

• Overestimation of Severity: Including prior deficits can lead to overestimation of stroke severity, potentially affecting clinical decisions 2

Special Considerations

• Documentation: While prior deficits should not be included in the NIHSS score, they should be documented separately in the patient's medical record for comprehensive care planning 1

• Baseline Function: Knowledge of the patient's baseline neurological function is important for overall clinical assessment but should not influence NIHSS scoring 2

• Certification: All professionals involved in stroke care should be trained and certified in NIHSS assessment to ensure proper administration and scoring 1, 2

By focusing only on current stroke-related deficits, the NIHSS provides a standardized measurement that accurately reflects stroke severity and supports appropriate clinical decision-making for optimal patient outcomes.