What constitutes a disabling stroke in a patient with a low National Institutes of Health Stroke Scale (NIHSS) score that requires thrombolysis?

Disabling Stroke Assessment in Patients with Low NIHSS Scores

A disabling stroke requiring thrombolysis in patients with low NIHSS scores should be defined by the presence of deficits that impact functional independence, regardless of the specific NIHSS score, as even patients with NIHSS scores <5 can have poor outcomes without treatment.

Understanding Disabling Stroke with Low NIHSS

The NIHSS score alone does not fully capture the disabling nature of a stroke. While higher NIHSS scores generally correlate with worse outcomes, even patients with low scores can experience significant functional impairment.

NIHSS Score Interpretation

• The American Academy of Neurology categorizes stroke severity as follows 1:

  • Small stroke: NIHSS <5
  • Moderate stroke: NIHSS 5-15
  • Large stroke: NIHSS >20

• However, different NIHSS cutoffs apply for anterior versus posterior circulation strokes:

  • For anterior circulation strokes, an NIHSS score of 8 best predicts outcomes
  • For posterior circulation strokes, an NIHSS score of 4 is the optimal cutoff 2

What Constitutes a Disabling Stroke

A disabling stroke should be defined functionally rather than by NIHSS score alone. The following factors should be considered:

Functional Impact Assessment

• Disabling deficits include those that would impact the patient's ability to perform activities of daily living independently, regardless of NIHSS score
• Modified Rankin Scale (mRS) provides context for disability:
  • mRS 0-1: No significant disability
  • mRS 2: Slight disability (unable to carry out all previous activities but able to look after own affairs without assistance)
  • mRS 3-6: Moderate to severe disability or death 3

Types of Deficits That May Be Disabling Despite Low NIHSS

• Language deficits
• Motor deficits affecting dominant hand
• Visual field deficits
• Gait disturbance
• Coordination problems

Research shows that the specific type of neurological deficit is not independently predictive of long-term prognosis in mild stroke patients, arguing against withholding treatment based solely on the perception that certain deficits are "non-disabling" 4.

Thrombolysis Decision-Making for Low NIHSS Strokes

Evidence for Treatment

• Up to 30% of stroke patients initially presenting with non-disabling or mild deficits may experience poor functional outcomes 5
• For patients with NIHSS 2-5, intravenous thrombolysis was associated with higher rates of excellent outcomes (mRS 0-1) at three months (adjusted OR 1.21, CI 1.08-1.34) 5
• MRI-based selection for thrombolysis in patients with NIHSS ≤5 showed a favorable safety profile with <1% symptomatic intracerebral hemorrhage 6

Posterior Circulation Considerations

• Patients with posterior circulation strokes often present with lower NIHSS scores but may still have poor outcomes 2
• For posterior circulation strokes, an NIHSS cutoff of 2 achieves >80% sensitivity for detecting patients with subsequent poor outcomes 2
• The European Stroke Organisation suggests using IVT up to 24 hours for basilar artery occlusion unless otherwise contraindicated 3

Risk-Benefit Assessment

• For patients with NIHSS 0-1, thrombolysis was associated with:

  • Higher risk of early neurological deterioration (adjusted OR 8.84, CI 6.61-11.83)
  • Higher risk of symptomatic ICH (adjusted OR 9.32, CI 4.53-19.15)
  • Lower rate of excellent outcomes at three months (adjusted OR 0.67, CI 0.5-0.9) 5

• For patients with NIHSS 3-5, thrombolysis showed better functional outcomes at discharge compared to those with NIHSS 0-2 (48.7% vs 81.3%) 7

Decision Algorithm for Thrombolysis in Low NIHSS Strokes

1. Assess NIHSS score and stroke location:

   • Anterior circulation: Consider NIHSS ≥4 potentially disabling
   • Posterior circulation: Consider NIHSS ≥2 potentially disabling

2. Evaluate functional impact:

   • Would the deficit impact the patient's independence or quality of life?
   • Is the deficit in a functionally critical area (dominant hand, language, vision, gait)?

3. Consider imaging findings:

   • Presence of large vessel occlusion
   • Core/perfusion mismatch on advanced imaging
   • For patients within 4.5-9 hours with CT or MRI core/perfusion mismatch, consider thrombolysis 3

4. Assess for disabling deficits despite low NIHSS:

   • Language deficits affecting communication
   • Motor deficits affecting dominant hand function
   • Visual field deficits affecting daily activities
   • Balance/coordination deficits affecting mobility

Common Pitfalls to Avoid

1. Relying solely on NIHSS score: The NIHSS may underestimate posterior circulation strokes and functionally significant deficits.

2. Assuming mild deficits will resolve: Up to 30% of patients with mild deficits may have poor outcomes without treatment.

3. Withholding treatment based on deficit type: Research does not support withholding treatment based on perception of certain deficits as "non-disabling."

4. Delaying treatment: Even for mild strokes, earlier treatment correlates with better outcomes.

5. Overlooking posterior circulation strokes: These often present with lower NIHSS scores but may have poor outcomes without treatment.