Development of a new comorbidity index for adults with cerebral palsy and comparative assessment with common comorbidity indices

AIM To develop a new comorbidity index for adults with cerebral palsy (CP), the Whitney Comorbidity Index (WCI), which includes relevant comorbidities for this population and better predicts mortality than the Charlson Comorbidity Index (CCI) and Elixhauser Comorbidity Index (ECI). METHOD Data from the Optum Clinformatics Data Mart was used for this retrospective cohort study. Diagnosis codes were used to identify adults aged 18 years or older with CP (n=1511 females, n=1511 males; mean [SD; range] age=48y [19y 2mo; 18-89y]) and all comorbidities in the year 2014. The WCI was developed based on the comorbidities of the CCI and ECI and other relevant comorbidities associated with 2-year mortality using Cox regression and competing risk analysis. The WCI was examined as unweighted (WCIunw ) and weighted (WCIw ). The model fit and discrimination (C-statistic) of each index was assessed using Cox regression. RESULTS Twenty-seven comorbidities were included in the WCI; seven new comorbidities that were not part of the CCI or ECI were added. The WCIunw and WCIw showed a better model fit and discrimination for 1- and 2-year mortality compared to the CCI and ECI. The WCIunw and WCIw were strong predictors for 1- and 2-year mortality (C-statistic [95% confidence interval] ranging from 0.81 [0.76-0.85] to 0.88 [0.82-0.94]). INTERPRETATION The new WCI, designed to include clinically relevant comorbidities, provides a better model fit and discrimination of mortality for adults with CP. WHAT THIS PAPER ADDS Common comorbidity indices exclude relevant comorbidities for adults with cerebral palsy (CP). A new comorbidity index for adults with CP was created by harmonizing clinical theory and data-driven methods. The Whitney Comorbidity Index better predicted 1- and 2-year mortality than other commonly used comorbidity indices.