Meghana Srinivas, MD

Bres-Bullrich M, Fridman S, Sposato LA. Relative Effect of Stroke Severity and Age on Outcomes of Mechanical Thrombectomy in Acute Ischemic Stroke. Stroke. 2021;52:2846–2848.

In this article by Maria Bres-Bullrich et al., the authors discuss the utilization of prognostic tools in determining functional outcomes in patients with acute ischemic due to an anterior circulation large vessel occlusion (LVO) with or without mechanical thrombectomy (MT). Mechanical thrombectomy (MT) is the standard of care for patients presenting with anterior circulation LVO. However, not all patients who receive MT benefit in a similar way. Stroke severity and age, which are readily available, are strong determinants of outcomes in patients receiving MT in clinical trials, and they heavily influence the decision to perform MT. However, there is a possible discrepancy between observational studies and clinical trials, with the former showing older age group (≥80 years) is associated with lower likelihood of shift to better outcomes and higher rates of death. In real-world practice, the interplay between stroke severity and age, as well as the relative weight of each variable on outcomes, are poorly understood.

This article has compared and summarized indices that have used NIHSS and age as prognostic tools to reliably predict outcomes of patients undergoing IV thrombolysis or MT. The first index discussed is the stroke prognostication using Age and NIHSS (SPAN) index. This is obtained by adding age and the baseline score and then classifying patients into SPAN-100 positive (SPAN ≥100) or SPAN-100 negative (≤100); retrospective data from National Institute of Neurological Disorders and stroke tPA trials showed favorable outcomes in SPAN-100 negative patients.

The next one is a brief discussion of the Stroke Checkerboard (SC) used by the Paris Stroke Consortium registry. The SC assigned 1 point per decade between 50 and 90 years of age and 2 points for every increase in 5 points on the NIHSS; SC <- 8 were associated with good functional outcomes versus scores >-12 (mRS 0-2 versus 4-6) at 90 days.

They have discussed in detail the modified version of the SPAN index called the weighted SPAN index (wSPAN), which was based on a cohort of 1750 patients from seven randomized controlled trials of MT from the HERMES collaboration. This was proposed by Ospel et al., who applied logistic regression analysis to estimate the co-efficient for age and NIHSS in relation to good functional outcomes (mRS 0-2), which was their primary end point, and excellent (mRS 0-1) and moderate outcome (0-3 mRS) were secondary end points at 90 days. The wSPAN index was deduced by calculating the ratio between both variables; the resulting NIHSS/age ratio for good outcome was rounded to 3 yielding a wSPAN index of age+3xNIHSS.

On independent adjusted models for wSPAN and SPAN 100 index, the area under curve (AUC) of the wSPAN showed a significantly better discriminative performance than that of the SPAN-100 index for the primary and secondary outcomes among the whole study cohort, and for each intervention arm. The association between wSPAN scores and the odds of good functional outcome did not differ between treatment arms, and MT was associated with good functional outcomes across all wSPAN data.

The authors have also spoken in detail about the limitations of the study, which are mainly the performance of the wSPAN composed of ONLY NIHSS scores and age. The wSPAN index was calculated from RCT with rigorous exclusion and inclusion criteria. The wSPAN would be expected to outperform the SPAN-100 index because it was developed in the same dataset in which it was tested versus the latter, which was derived and validated in different cohorts.

This study highlights the results and implications of the wSPAN index, which showed lack of interaction between NIHSS score and age, suggesting that each variable has its own effect on stroke outcome. The second important implication is the relative adjusted association of stroke severity and age with the likelihood of a good outcome, with one point increase in NIHSS score approximating a 3-year increase in age. The third implication is that MT was beneficial for the whole spectrum of NIHSS and age combinations, hence, decision to perform MT should be done on a case-to-case basis and not solely relying on prognostic tools.  

We have learned that stroke severity and age can have an independent impact on the odds of functional outcome in patients with acute ischemic stroke due to anterior circulation LVO. As reviewed here, there are prognostic tools available to reliably predict functional outcomes with or without MT; however, the value of these tools can be used to aid in discussion with patients and their families about possible functional outcomes and to decide whether MT should be performed or not.

Larger multicenter studies need to be performed for external validation and calibration of prognostic tools.