Which patients with a low National Institutes of Health Stroke Scale (NIHSS) score should be considered for thrombolysis?

Thrombolysis in Patients with Low NIHSS Scores

Patients with low NIHSS scores (0-5) should be considered for thrombolysis if they have potentially disabling symptoms, despite the low score. 1

Understanding Low NIHSS Scores and Stroke Outcomes

The National Institutes of Health Stroke Scale (NIHSS) is a valuable prognostic tool, but relying solely on a low score to withhold treatment can lead to poor outcomes:

• Approximately one-third of patients not treated with intravenous rtPA due to mild or rapidly improving symptoms have poor final outcomes 1
• Certain deficits may be potentially disabling despite low NIHSS scores:
  • Isolated aphasia
  • Isolated hemianopia
  • Gait disturbance
  • Other symptoms that could significantly impact quality of life

Risk-Benefit Assessment for Low NIHSS Patients

Benefits of Thrombolysis in Low NIHSS Patients

• Can prevent neurological deterioration in patients with persistent large vessel occlusion
• May improve outcomes in patients with NIHSS 2-5, who show higher rates of excellent outcomes (mRS 0-1) at three months with thrombolysis 2

Risks of Thrombolysis in Low NIHSS Patients

• Patients with NIHSS scores <10 have only a 3% risk of symptomatic intracranial hemorrhage (sICH) compared to 18% in those with NIHSS >20 3, 1
• In patients with NIHSS 0-1, thrombolysis may be associated with:
  • Higher risk of early neurological deterioration
  • Higher risk of sICH
  • Lower rates of excellent outcomes at three months 2

Decision Algorithm for Thrombolysis in Low NIHSS Patients

1. Evaluate for potentially disabling symptoms despite low NIHSS:

   • Isolated aphasia
   • Isolated hemianopia
   • Gait disturbance
   • Other symptoms impacting quality of life

2. Assess for large vessel occlusion (LVO):

   • Persistent LVO on imaging increases risk of subsequent deterioration 1
   • Consider CT angiography or MR angiography

3. Consider time from symptom onset:

   • Treatment within 4.5 hours of symptom onset is recommended for eligible patients 1
   • Earlier treatment correlates with better outcomes

4. Stratify by NIHSS subgroups:

   • NIHSS 2-5: Consider thrombolysis as benefit is more established 2
   • NIHSS 0-1: Exercise caution as benefit is less clear and potential harm signals exist 2

5. Assess for contraindications:

   • Blood pressure >185/110 mmHg (must be controlled before thrombolysis) 1, 3
   • Blood glucose abnormalities
   • Recent anticoagulant use
   • Other standard contraindications

Special Considerations

Imaging Considerations

• CT-ASPECTS ≥9 with NIHSS ≥8 (clinical-CT mismatch) predicts better response to thrombolysis 4
• However, CT-NIHSS mismatch does not reliably correlate with MRI diffusion-perfusion mismatch 5

Mechanical Thrombectomy Considerations

• Current guidelines recommend mechanical thrombectomy for patients with NIHSS ≥6 1
• Emerging evidence suggests mechanical thrombectomy may be beneficial in selected patients with NIHSS <6 and large vessel occlusion 6, 7
• If eligible for both, patients should receive IV thrombolysis even if mechanical thrombectomy is being considered 1

Monitoring After Thrombolysis

For patients receiving thrombolysis, implement strict monitoring:

• Blood pressure monitoring: Every 15 minutes for 2 hours, every 30 minutes for 6 hours, then hourly for 16 hours 3
• Neurological assessments using standardized tools 3
• Monitor for signs of hemorrhage:
  • Change in level of consciousness
  • Neurological deterioration
  • New headache
  • Nausea and vomiting
  • Elevation in blood pressure 3

Key Pitfalls to Avoid

1. Withholding treatment based solely on low NIHSS score when potentially disabling symptoms are present
2. Ignoring signs of large vessel occlusion in patients with mild symptoms
3. Failing to recognize that certain deficits (aphasia, hemianopia) can be severely disabling despite low NIHSS scores
4. Delaying treatment while waiting for symptom progression
5. Treating all low NIHSS patients the same without considering the specific NIHSS subgroup (0-1 vs. 2-5)