Missing outcome data is common and ‘does not occur at random’ in thrombectomy registries

Timo Uphaus (L), Marianne Hahn

The phenomenon of missing outcome data (MOD) within stroke registries of mechanical thrombectomy cases “is not a rare event and does not occur completely at random”. That is a key concluding message from research carried out and recently published in the Journal of NeuroInterventional Surgery (JNIS) by Timo Uphaus, Marianne Hahn (both University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany) and colleagues.

“We have reported factors associated with missing data on 90-day functional outcome in a large, multicentre registry of mechanical thrombectomy in acute stroke care,” Uphaus, Hahn et al state in their JNIS article. “These include patients with higher pre-stroke disability; patients treated later after symptom onset; patients not receiving bridging IVT [intravenous thrombolysis]; and patients with relevant disability at discharge from the treating hospital, which are at increased risk of MOD.

“These patient groups may therefore be underrepresented in acute stroke care studies based on complete case analysis, compared with the actual cohort treated by mechanical thrombectomy. In contrast, patients with inhouse mortality after mechanical thrombectomy treatment are likely to have complete data on 90-day stroke outcome and might therefore be disproportionately present. In addition to patients with higher pre-stroke and post-stroke disability, increased efforts to perform 90-day follow-up should also be undertaken for patients with a shorter duration of hospital stay, and those discharged to institutional care or hospital.”

The authors initially aver that MOD is a “common problem” in clinical trials and registries—especially in analyses based on complete cases—and creates a potential bias when drawing conclusions from these data. They go on to note that identifying factors associated with MOD may help to increase follow-up rates and assess the need for imputation strategies and, as such, they set about investigating MOD in a multicentre, prospective registry study of mechanical thrombectomy for large vessel occlusion (LVO) ischaemic stroke.

“While registries depicting mechanical thrombectomy in routine care are valuable tools to analyse patterns of care and functional outcome after LVO in distinct populations, missing data may impact the accuracy and generalisability of these analyses,” the authors add. “Bias may result from case selection on the basis of complete data and cannot be fully adjusted for by imputation of missing data, because MOD is significantly dependent on other observed (and unobserved) variables, and the outcome itself.”

Uphaus, Hahn and colleagues analysed a total of 13,082 patients enrolled in the German stroke registry-endovascular treatment (GSR-ET) from May 2015 to December 2021 with regard to MOD (90-day modified Rankin scale [mRS]). The authors detail that univariate logistic regression analyses were used to identify factors that were unbalanced between patients with and without MOD, while subgroup analyses were performed to identify patients for whom increased efforts to perform clinical follow-up after hospital discharge are needed as well.

Some 19.7% of these patients were identified as having MOD at 90-day follow-up. MOD was found to be more common with higher (mRS 3–5) compared to lower (mRS 0–2) pre-stroke disability (32.2% vs 13.7%, respectively), as well as with higher post-stroke disability upon discharge (odds ratio [OR]=1.234). In addition, absence of bridging IVT and longer time to treatment were associated with a greater rate of MOD—but MOD was less common with futile recanalisation (thrombolysis in cerebral infarction [TICI] score of 0–2a) versus successful recanalisation (TICI 2b–3; 12.4% vs 15%, respectively). In patients discharged alive with well-documented baseline characteristics, the authors also report shorter hospital stay (OR=0.992), and discharge to institutional care or hospital (OR=1.754), as being associated with MOD.

“MOD in routine-care mechanical thrombectomy registry data was not random,” Uphaus, Hahn et al conclude. “Increased efforts to perform clinical follow-up are needed, especially in the case of higher pre-stroke and post-stroke disability, and discharge to hospital or institutional care. Increased follow-up rates may then also improve the validity and generalisability of findings from routine care mechanical thrombectomy datasets.”

In their JNIS paper, the authors highlight the strengths of their analysis, including usage of an “up-to-date, large and complex nationwide cohort” of more than 13,000 thrombectomy procedures, creating a “strong data foundation”. And, because 30 centres were involved in enrolment and data acquisition took place over more than six years, they report being able to “minimise the impact of site- and time-specific factors influencing MOD”.

However, Uphaus, Hahn and colleagues also acknowledge several limitations hampering their research, such as the fact they did not capture sociodemographic characteristics and other, additional patient factors previously reported as being associated with missing data, as well as “unique organisational structures” potentially restricting the generalisability and transferability of these results to other stroke registries.


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