Background and objectives: The clinical course and outcome of the Guillain-Barré syndrome (GBS) are diverse and vary among regions. The modified Erasmus GBS Outcome Score (mEGOS) is a clinical model that predicts the risk of walking inability in GBS patients, and was developed with data from Dutch patients. The study objective was to validate the mEGOS in the International GBS Outcome Study (IGOS) cohort and to improve its performance and region-specificity. Methods: We used prospective data from the first 1500 patients included in IGOS, aged ≥ 6 years and unable to walk independently. We evaluated if the mEGOS at entry and week 1 could predict the inability to walk unaided at 4 and 26 weeks in the full cohort and in regional subgroups, using two measures for model performance: (1) discrimination: area under the receiver operating characteristic curve (AUC), and (2) calibration: observed versus predicted probability of being unable to walk independently. To improve the model predictions we recalibrated the model containing the overall mEGOS score, without changing the individual predictive factors. Finally, we assessed the predictive ability of the individual factors. Results: For validation of mEGOS at entry 809 patients were eligible (Europe/North America n=677, Asia n=76, other=56), and 671 for validation of mEGOS at week 1 (Europe/North America n=563, Asia n=65, other=43). AUC-values were >0.7 in all regional subgroups. In the Europe/North America subgroup observed outcomes were worse than predicted, while in Asia observed outcomes were better than predicted. Recalibration improved model accuracy and enabled the development of a region-specific version for Europe/North America (mEGOS-Eu/NA). Similar to the original mEGOS, severe limb weakness and higher age were the predominant predictors of poor outcome in the IGOS cohort. Discussion: The mEGOS is a validated tool to predict the inability to walk unaided at 4 and 26 weeks in GBS patients, also in countries outside The Netherlands. We developed a region-specific version of mEGOS for patients from Europe/North America. Classification of evidence: This study provides Class II evidence that the mEGOS accurately predicts the inability to walk unaided at 4 and 26 weeks in GBS patients. Clinicaltrialsgov identifier: NCT01582763
