Meta-analysis of cognitive functioning in patients following kidney transplantation

Background
Evidence is mixed regarding the nature of cognitive function in patients who have undergone renal transplantation. The aim of this meta-analysis was to examine which cognitive domains are impacted following kidney transplantation and how performance compares to non-transplanted patients or healthy controls/normative data.

Method
A systematic search was conducted using keywords within three databases (EMBASE, Medline and PsychINFO), yielding 458 unique studies; ten of which met the inclusion criteria. Neuropsychological tests were grouped into nine cognitive domains and three separate analyses were undertaken within each domain; (1) within subjects: pre vs. post- transplant; (2) transplanted vs. non transplanted patients; (3) transplanted vs. healthy matched controls and standardised normative data.

Results
Transplanted patients showed moderate to large improvements in the domains of general cognitive status (g = 0.526), information and motor speed (g = 0.558), spatial reasoning (g = 0.376), verbal memory (g = 0.759), visual memory (g = 0.690) when compared to their pre-operative scores. Test scores in the same five domains were significantly better in post-transplanted patients when compared to dialysis-dependant or conservatively managed chronic kidney disease (CKD) patients. However post-transplanted patients performance was significantly below that of healthy controls (and standardised normative data) in the domains of executive functioning (g = -0.283), verbal fluency (g = -0.657) and language (g = -0.573).

Conclusions
Two key issues arise from this review. First, domain-specific cognitive improvement occurs in patients after successful transplantation. Nevertheless, transplanted patients still performed significantly below healthy levels in some domains. Second, there are important shortcomings in existing studies; the length of follow-up is typically short and only limited neuropsychological test batteries are employed. These factors are important in order to support the recovery of cognitive function among patients following renal transplant.