What is the target NIHSS (National Institutes of Health Stroke Scale) score for thrombolysis?

NIHSS Score Targets for Thrombolysis in Acute Ischemic Stroke

Patients with NIHSS scores between 5-20 are the optimal candidates for thrombolysis, as they demonstrate the best benefit-risk ratio, while those with scores >20 have significantly higher bleeding risks that may outweigh potential benefits. 1

Risk Stratification by NIHSS Score

• Patients with NIHSS scores <10 have only a 3% risk of symptomatic intracranial hemorrhage (sICH) following thrombolysis 2
• Patients with NIHSS scores between 10-20 have an intermediate risk of hemorrhagic complications 2, 1
• Patients with NIHSS scores ≥20 have a 17-18% risk of symptomatic intracranial hemorrhage, substantially increasing the risk-benefit concerns 2, 1
• All symptomatic intracranial hemorrhages in the PROACT-II trial occurred in patients with baseline NIHSS scores ≥11 2, 1

Efficacy Considerations by NIHSS Score

• Patients with NIHSS scores <10 have a 60-70% chance of favorable outcome at 1 year, regardless of treatment 2, 1
• Patients with NIHSS scores >20 have only a 4-16% chance of favorable outcome at 1 year, even with treatment 2, 1
• The benefit of thrombolysis appears most pronounced in patients with moderate stroke severity (NIHSS 5-20) 2, 1

Special Considerations for Mild Strokes (NIHSS ≤5)

• Patients with mild strokes (NIHSS ≤5) but with large vessel occlusions may benefit significantly from thrombolysis 3
• Non-thrombolysed patients with mild deficits and large vessel occlusion deteriorated significantly more often within 3 months than thrombolysed patients (41.4% vs 15%, p<0.001) 3
• Among mild strokes, those with NIHSS 0-2 have better outcomes after thrombolysis compared to those with NIHSS 3-5 (81.3% vs 48.7% excellent outcomes) 4

Clinical Decision Algorithm

1. NIHSS <5 with large vessel occlusion: Consider thrombolysis as these patients show benefit with low bleeding risk (symptomatic ICH <5%) 5, 3
2. NIHSS 5-10: Strong candidate for thrombolysis with favorable benefit-risk profile (low 3% sICH risk with good potential for recovery) 2, 1
3. NIHSS 11-20: Consider thrombolysis with careful monitoring (moderate bleeding risk but still favorable benefit-risk ratio) 2, 1
4. NIHSS >20: Exercise caution due to high bleeding risk (17-18% sICH) and poor prognosis regardless of treatment; individualized decision-making is critical 2, 1

Post-Thrombolysis Monitoring Based on NIHSS

• All patients receiving thrombolysis should have frequent neurological assessments, including abbreviated NIHSS evaluations 2
• Complete NIHSS assessment should be performed on admission and if there is evidence of neurological decline 2
• Blood pressure should be monitored every 15 minutes for 2 hours, every 30 minutes for the next 6 hours, and then hourly until 24 hours after thrombolysis 2
• Patients with higher NIHSS scores require more vigilant monitoring for signs of hemorrhagic transformation 2, 1

Prognostic Value of 24-Hour NIHSS

• A 24-hour post-thrombolysis NIHSS score ≤10 is strongly associated with good functional outcome at 90 days 6
• The threshold NIHSS score for predicting unfavorable outcomes changes from 12 at admission to 5 at 24 hours after thrombolysis 7
• The predictive power of NIHSS for functional outcomes increases over time, peaking at 10 days after treatment 7

Common Pitfalls and Caveats

• Focusing solely on NIHSS score without considering other factors (age, time from onset, imaging findings) may lead to suboptimal treatment decisions 2
• Patients with mild symptoms (low NIHSS) often face delays in transport, imaging, and treatment, potentially reducing the benefits of thrombolysis 5
• The presence of large vessel occlusion may warrant thrombolysis even with low NIHSS scores, as these patients have high risk of deterioration without treatment 3
• Advanced age, elevated blood pressure, blood glucose >200 mg/dL, and prior head trauma increase hemorrhage risk independent of NIHSS score 2