Cognitive Function and Kidney Transplantation: Putting Current Data into Clinical Perspective

Pretransplant Cognitive Function and Kidney Transplant Outcomes: A Prospective Cohort Study

Background & Hypothesis

Cognitive impairment is common in patients being evaluated for a kidney transplant (KT). The association between pretransplant cognitive function and posttransplant outcomes is unclear.

Study Design

We performed a prospective cohort study to assess the association between pretransplant cognitive function and clinically relevant posttransplant outcomes.

Setting and Population

In this single center study, participants from the transplant clinic were evaluated during their pretransplant clinic visits and followed prospectively.

Outcomes

Our primary outcome measure was allograft function. Secondary outcomes were length of hospitalization for KT, hospital readmission within 30 and 90 days, graft loss, graft rejection within 90 days and 1 year, and mortality.

Analytic Approach

We measured cognitive function with the Montreal Cognitive Assessment (MoCA) test. We assessed the association of pretransplant MoCA score with posttransplant outcomes; we used linear mixed effects models to assess the association with the change in estimated glomerular filtration rate, Poisson regression for length of hospitalization, Cox proportional hazard model for graft loss and mortality, and a logistic regression model for readmission and rejection.

Results

We followed 501 participants for 2.7 ± 1.5 years. The mean age of the patients was 53 ± 14 years and the mean pretransplant MoCA score was 25 ± 3. Lower pretransplant MoCA scores did not adversely affect the primary outcome of allograft function or the secondary outcomes. Although higher MoCA scores predicted a higher decline in graft function (β = -0.28, 95% CI: -0.55 to -0.01, P = 0.04), the effect was small and not clinically significant. Older age was associated with longer hospitalization, lower likelihood of rejection, and higher mortality. Deceased donor KT (vs living donor KT) was associated with longer hospitalization but better graft function. Longer time receiving dialysis before KT was associated with longer hospitalization. A history of diabetes mellitus was associated with higher mortality.

Limitations

Single center study limiting generalizability.

Conclusions

Pretransplant MoCA scores were not associated with the primary outcome of allograft function or the secondary outcomes.

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

RATIONALE & OBJECTIVE

Kidney disease negatively affects cognition. We assessed the effect of kidney transplantation (KT) on different cognitive domains.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

We examined pre- versus post-KT cognition in patients waitlisted for KT at an academic center.

PREDICTORS

Transplant status. We measured cognitive function before KT (n=101), 3 months after KT (n=78), and 1 year after KT (n = 83).

OUTCOMES

Our primary outcome was change in cognitive function before versus after 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], Trail Making Test [TMT] A), working memory/attention (Digit Span), executive function (TMT B), and semantic memory/verbal fluency/language (Category Fluency).

ANALYTICAL APPROACH

Using linear mixed model analysis, we evaluated the changes in neuropsychological test scores adjusted for age, sex, race, education, and number of assessments.

RESULTS

Before KT, Logical Memory I and II, DSST, MMSE, Category Fluency (animal naming), and Digit Span backward scores were low compared with normative values from the National Alzheimer's Coordinating Center data. Logical Memory I and II scores improved after 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 TMT A and B scores did not change after KT.

LIMITATIONS

Single-center study.

CONCLUSIONS

Episodic 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 therefore at least partly reversible with KT.

PLAIN-LANGUAGE SUMMARY

Cognitive impairment in kidney disease affects self-esteem, vocational abilities, quality of life, health care costs, and mortality. It is not clear whether kidney transplantation (KT) improves cognition and whether the improvement is uniform across cognitive domains. The distinction between reversible and irreversible cognitive impairment has important implications in the clinical care of patients before and after KT. We assessed cognition before KT and 3 months and 12 months after KT and discovered that episodic and verbal declarative memory normalized with KT. Semantic memory, verbal fluency, language, psychomotor speed, and visuospatial function also improved with KT but did not reach normal levels. Cognitive impairment in kidney disease is therefore at least partly reversible.