Changes in Cognitive Function After Kidney Transplantation: A Longitudinal Cohort Study

Rationale & ObjectiveKidney disease negatively affects cognition. We assessed the effect of kidney transplantation (KT) on different cognitive domains.Study DesignProspective cohort study.Setting & ParticipantsWe examined pre- to post-KT cognition in patients waitlisted for KT at an academic center.PredictorsTransplant status. We measured cognitive function pre-KT (n=101), three months post-KT (n=78), and 1-year post-KT (n=83).OutcomesOur primary outcome was change in cognitive function pre- to post-KT. We used standard neuropsychological tests to assess global cognition (Mini Mental State Exam MMSE, episodic/declarative memory (Logical Memory), psychomotor speed/visuospatial function (Digit Symbol Substitution Test DSST, Trailmaking A), working memory/attention (Digit Span), executive function (Trailmaking B), and semantic memory/verbal fluency/language (Category Fluency).Analytical ApproachUsing linear mixed model analysis, we evaluated the change in neuropsychological test scores adjusted for age, sex, race, education, and number of assessments.ResultsLogical Memory I and II, DSST, MMSE, Category Fluency (animal naming), and Digit Span backward scores were low pre-KT compared to normative values from the National Alzheimer's Coordinating Center data. Logical memory I and II improved post-KT (pre- vs. post-KT: estimated group difference (d)=3.3, p<0.001 for Logical Memory I, d=4.27, p<0.001 for Logical Memory II), such that post-KT scores were similar to normative values (post-KT vs. normative values: d=-0.37, p=0.06 for Logical Memory I, d=-0.89, p=0.08 for Logical Memory II). Category Fluency (animal naming) (d=2.4, p<0.001) and DSST (d=3.12, p=0.01) scores also improved with KT, but post-KT DSST scores remained lower than normative values (post-KT vs. normative values: d=-5.17, p<0.001). MMSE, Digit Span, and Trailmaking A and B did not change with KT.LimitationsSingle center study.ConclusionsEpisodic and verbal declarative memory normalize after KT. Semantic memory, verbal fluency, language, psychomotor speed, and visuospatial function show partial improvement. Cognitive impairment in kidney disease is thus, at least partly reversible with KT.