Charlson comorbidity index applied to shunted idiopathic normal pressure hydrocephalus

Abstract

A series of epidemiological studies have shown the limited life expectancy of patients suffering from idiopathic normal pressure hydrocephalus (iNPH). In most cases, comorbid medical conditions are the cause of death, rather than iNPH. Though it has also been shown that shunting improves both life quality and lifetime. We sought to investigate the utility of the Charlson comorbidity index (CCI) for improved preoperative risk-benefit assessment of shunt surgery in individual iNPH cases. 208 shunted iNPH cases were prospectively investigated. Two in-person follow up visits at 3 and 12 months assessed postoperative clinical status. The correlation of the age adjusted CCI with survival was investigated over the median observation time of 2.37 years (IQR 1.16-4.15). Kaplan Meier statistics revealed that patients with a CCI score of 0-5 have a 5-year survival rate of 87%, compared to only 55% in patients with CCI > 5. Cox multivariate statistics revealed that the CCI was an independent predictor of survival, while common preoperative iNPH scores (modified Rankin Scale (mRS), gait score, and continence score) are not. As expected, mRS, gait, and continence scores improved during the postoperative follow up period, though relative improvement on any of these was not predicted by baseline CCI. The CCI is an easily applicable preoperative predictor of survival time in shunted iNPH patients. The lack of a correlation between the CCI and functional outcome means that even patients with multiple comorbidities and limited remaining lifetime may appreciate benefit from shunt surgery.

Figure 1

Kaplan–Meier analysis of survival time versus CCI, mRS, gait and continence score. The log rank test revealed significant differences between the low and high score groups of CCI, mRS and gait, but not continence score. The 95% confidence intervals and censoring of cases are shown.

Figure 2

Stacked proportional bar graphs of mRS, gait and continence scores. Postoperative follow-up examinations show a significant improvement of the three categories. Yellow indicates moderate impairment, red and orange are worse, blue, and green are better.

Figure 3

Linear regression analysis of changes of the clinical score at the follow-up as compared with the preoperative scores was not related to the preoperative CCI. The regression line is shown and in addition the individual data visualized as jitter plot. The jitter plot is like a scatter plot but adds random noise to better see the information contained in the data, when there is a lot of overplotting.