Group changes in cognitive performance after surgery mask changes in individual patients with glioblastoma

Object: 
There is a growing interest to include evaluations of cognitive performance in the clinical management of patients with Glioblastoma (GBM). However, as changes in cognitive performance of a group may mask changes in individual patients, study results are often difficult to transfer into clinical practice. We focused on the comparison of group versus individual changes in neuropsychological performance of GBM patients after initial surgical treatment.
Methods: 
Patients underwent neuropsychological evaluation using CNS Vital Signs one day prior to, and three months after surgery. Two-tailed paired samples t-tests were conducted to assess changes on the group level. Reliable Change Indices (RCIs), that correct for practice effects and imperfect test-retest reliabilities, were used to examine change in individual patients.
Results: 
Cognitive dysfunction was common (>80%) both before and three months after surgery in this sample of 82 GBM patients. Whereas group analyses revealed minimal changes in performance over time, RCIs demonstrated that most patients (89%) showed changes in performance in at least one cognitive domain. Half of these individual patients solely showed improvements, a quarter solely showed declines, and another quarter showed both improvements and declines.
Conclusions: 
This study clearly demonstrates that important individual changes in performance are masked when looking only at group results. Future studies should more often use an individual patient approach to enhance knowledge transfer into clinical practice.