At what National Institutes of Health Stroke Scale (NIHSS) score should thrombolysis with tissue plasminogen activator (tPA) be avoided?

NIHSS Score Threshold for Thrombolysis in Acute Ischemic Stroke

Patients with NIHSS scores >20 should generally not receive thrombolysis due to significantly increased risk of symptomatic intracranial hemorrhage without proportional benefit in outcomes. 1

Risk of Intracranial Hemorrhage Based on NIHSS Score

• In the NINDS trial, patients with NIHSS scores ≥20 had a 17% risk of symptomatic intracranial hemorrhage (sICH) compared to only 3% in those with scores <10 1
• All symptomatic intracranial hemorrhages in the PROACT-II trial occurred in patients with baseline NIHSS scores ≥11, and the rate of symptomatic brain hemorrhage in NINDS was 18% for patients with NIHSS >20 1
• Stroke severity as measured by NIHSS is one of the strongest predictors of hemorrhagic transformation after thrombolysis 1

Efficacy Considerations by NIHSS Score

• Patients with very severe strokes (NIHSS >20) have only a 4-16% chance of favorable outcome at 1 year, regardless of treatment 1
• The benefit-risk ratio becomes increasingly unfavorable as NIHSS scores exceed 20 due to the substantially higher bleeding risk without proportional improvement in outcomes 1
• Some clinical trials have specifically avoided enrolling patients with very severe strokes (NIHSS >25-30) due to poor expected outcomes regardless of therapy 1

Special Considerations

• For patients with moderate stroke severity (NIHSS 5-14), thrombolysis shows better risk-benefit profile with potentially lower bleeding risk and better efficacy 2
• For mild strokes (NIHSS ≤4), the decision should not be based solely on NIHSS score but rather on the assessment of individual neurologic deficits and their functional impact 3
• Disabling deficits such as language impairment, hand paresis, and gait disorders may warrant thrombolysis even with low NIHSS scores if they significantly impact function 3

Monitoring After Thrombolysis

• All patients receiving thrombolysis should be monitored closely for at least 24 hours after treatment, particularly those with higher NIHSS scores 1
• Nursing staff should be trained to recognize signs of hemorrhagic transformation, including changes in level of consciousness, blood pressure elevation, deterioration in motor examination, new headache, or nausea and vomiting 1
• A hemorrhage protocol should be readily available for rapid response if bleeding is suspected 1

Clinical Algorithm for Decision-Making

1. For NIHSS >20: Generally avoid thrombolysis due to high bleeding risk (17-18%) and poor outcomes regardless of treatment 1
2. For NIHSS 5-20: Consider thrombolysis within appropriate time windows as benefit likely outweighs risk 1
3. For NIHSS <5: Evaluate for specific disabling deficits rather than relying solely on NIHSS score; thrombolysis may still be appropriate for functionally significant deficits 3

Remember that these recommendations focus on intravenous thrombolysis. For patients with large vessel occlusions and severe deficits, mechanical thrombectomy may be considered as an alternative or adjunctive treatment strategy 4, 5.