Endovascular therapy of large vessel acute ischemic stroke allows 1 additional patient to have fully restored neurologic function for every 7 patients treated and 1 additional patient to have improved neurologic function for every 3 to 5 patients treated.

May Nour, MD, PhD, University of California, Los Angeles, Los Angeles, California, USA, presented an analysis of the number needed to treat to benefit (NNTB) and the number needed to treat to harm (NNTH) from the MR CLEAN study [Berkhemer OA et al. N Engl J Med. 2015].

MR CLEAN was the first trial of thrombectomy using second-generation devices to demonstrate improved outcomes of intra-arterial treatment plus standard medical treatment compared with medical therapy alone, which included the use of intravenous tissue plasminogen activator. This prospective randomized design enrolled 500 patients in an open-label fashion with blinded end point evaluation.

The mean age of study participants was 65 years; 445 patients (89%) were treated with intravenous tissue plasminogen activator before randomization. Retrievable stents were used in 190 patients (81.5%) assigned to intra-arterial treatment. The 90-day modified Rankin scale (mRS) score—the primary outcome measure—showed a significant difference in favor of the intervention versus the control in analysis with univariable ordinal regression.

Dr Nour and colleagues sought to quantify the magnitude of the effect of the clinical improvement with intra-arterial treatment in MR CLEAN, using the size metrics of NNTB, NNTH, and the benefit per hundred (BPH) and harm per hundred treated.

They analyzed the magnitude of effect of the transitions across multiple mRS levels and for individual dichotomizations of the mRS. The following 3 analysis methods were used: joint outcome algorithmic specification, permutation analysis (Mann-Whitney test), and expert-dependent joint outcome analysis using 8 independent experts (3 stroke neurologists, 1 interventional neurologist, 2 interventional neuroradiologists, and 2 endovascular neurosurgeons).

As calculated by the absolute risk reduction in the dichotomized analysis (Table 1), the best NNTB was 6.6 and the best net BPH was 15, whereas the other 3 methods of analysis produced a much lower NNTB but a much higher BPH (Table 2).

When the results are considered together, the use of endovascular therapy compared with medical therapy alone will result in 1 of 7 treated patients not having a disability and 1 of every 3 to 5 treated patients having a lesser degree of disability, said Dr Nour. Among 100 patients treated with endovascular therapy, 15 will not have a disability and 23 to 32 will have a lesser degree of disability compared with that of patients treated with medical therapy.

This analysis of the magnitude of the treatment effect in MR CLEAN provides useful information for patients, caregivers, and physicians involved in acute stroke care, she concluded.