Should a thrombectomy be done in an elderly patient with an occluded M2 (Middle Cerebral Artery) on the left with a mild to moderate stroke severity (National Institutes of Health Stroke Scale (NIHSS) score of 6) and a pre-stroke modified Rankin Scale (mRS) score of 1-2, where thrombolysis is not possible?

Mechanical Thrombectomy for M2 Occlusion with NIHSS 6 in Elderly Patient

Thrombectomy may be reasonable for this elderly patient with M2 occlusion and NIHSS 6, though the evidence is less certain than for M1 occlusions, and the decision should weigh the patient's functional baseline (pre-mRS 1-2) against procedural risks in the elderly population.

Guideline-Based Recommendation for M2 Occlusions

The American Heart Association/American Stroke Association provides a Class IIb recommendation (may be reasonable, uncertain benefit) for mechanical thrombectomy in M2 occlusions within 6 hours of symptom onset 1. This contrasts sharply with the Class I recommendation (strong evidence) for M1 and ICA occlusions 1.

Evidence Supporting M2 Thrombectomy

• The HERMES meta-analysis showed a favorable direction of treatment effect for M2 occlusions, but the adjusted common odds ratio was not statistically significant (1.28; 95% CI: 0.51-3.21) 1.

• Pooled data from SWIFT, STAR, DEFUSE 2, and IMS III demonstrated that reperfusion in M2 occlusions was associated with excellent functional outcomes (mRS 0-1; OR: 2.2; 95% CI: 1.0-4.7) 1.

• The technical goal remains achieving mTICI 2b/3 reperfusion to maximize functional outcomes 2.

NIHSS 6 Consideration

Your patient meets the NIHSS ≥6 threshold specified in guidelines for M1 occlusions 1, but this threshold was established primarily for proximal large vessel occlusions, not M2 segments.

Emerging Evidence for Lower NIHSS Scores

• A multicenter retrospective study showed that immediate thrombectomy in patients with NIHSS 0-5 and large vessel occlusions resulted in 84.4% good outcomes versus 70.1% with medical management (14.4% absolute difference, p=0.03) 3.

• Another study of 83 patients with NIHSS <6 demonstrated that thrombectomy was associated with smaller infarct size (p=0.04) and decreased mortality (p=0.03), though no difference in 90-day mRS 4.

• Baseline NIHSS was identified as a predictor of outcomes in M2 occlusions, with higher scores associated with worse outcomes 5.

Elderly Patient Considerations

Age alone should not exclude this patient from thrombectomy 6. The HERMES collaboration demonstrated that mechanical thrombectomy had a favorable effect in patients ≥80 years old (cOR: 3.68; 95% CI: 1.95-6.92) 1.

Critical Caveats for Elderly Patients

• The number of patients ≥90 years in major trials was very small, and benefit in this age group remains unclear 1.

• Comorbidities and procedural risks must be factored into decision-making for elderly patients 1.

• Despite improved outcomes with thrombectomy, elderly patients still have worse absolute outcomes than younger patients 6.

Pre-Stroke Functional Status

The patient's pre-mRS 1-2 is favorable and falls within the guideline-recommended range (pre-mRS 0-1 for Class I recommendation in M1 occlusions) 1. A pre-mRS of 2 represents slight disability but independence, making functional recovery more achievable.

Technical and Safety Considerations for M2

• M2 thrombectomy achieves high recanalization rates: one study reported 93.3% TICI 2b/3 reperfusion for M2 versus 76.0% for M1 7.

• Stent retrievers and combined techniques are more effective than direct aspiration alone for M2 occlusions (OR: 9.2 and 2.6 respectively versus aspiration) 8.

• Intraprocedural subarachnoid hemorrhage risk is higher with stent retrievers (OR: 5.0) and combined techniques (OR: 4.6) compared to aspiration alone 8.

• No periprocedural complications occurred in M2 cases in one series, compared to 3 complications in M1 cases 7.

Time Window

If within 6 hours of symptom onset, the patient falls within the standard time window for M2 consideration 1, 2. For 6-24 hours, there are no specific guideline recommendations for M2 occlusions, and DAWN/DEFUSE-3 criteria would need strict application 2.

Practical Algorithm for This Case

Proceed with thrombectomy if:

• Within 6 hours of symptom onset
• ASPECTS ≥6 on imaging
• No extensive irreversible brain damage (ASPECTS 0 would be absolute contraindication) 6
• Patient/family goals align with aggressive intervention
• Experienced neurointerventionalist available

Exercise caution if:

• Patient age ≥90 years (very limited trial data) 1
• Significant comorbidities limiting life expectancy
• Very distal M2 branch (technical difficulty increases)

Key Pitfall to Avoid

Do not delay or withhold treatment to "wait and see" if symptoms improve 1. Every hour delay to reperfusion worsens disability outcomes (cOR: 0.84 per hour; ARD: -6.7%) 1. The decision must be made expeditiously.