Cognitive Impairment Among Kidney Transplant Recipients

As many as 50% to 87% of patients on maintenance dialysis experience cognitive impairment, influencing quality of life, employment rates, adherence to treatment, hospital admissions, health care costs, morbidity, and mortality. Kidney transplantation offers advantages in quality of life and survival over dialysis, but kidney transplant recipients have several risk factors for cognitive impairment, including comorbid illness, depression, and lower levels of physical activity.

There are few data on the prevalence of cognitive impairment in kidney transplant recipients. Aditi Gupta, MD, and colleagues at the University of Kansas Medical Center in Kansas City recently conducted a cross-sectional study designed to screen eligible kidney transplant recipients in order to evaluate the prevalence of cognitive impairment in that patient population. The researchers also sought to evaluate the factors associated with cognitive impairment in transplant recipients. Results of the study were reported online in BMC Nephrology [doi:10.1186/s12882-017-0570-1].

The single-center study followed eligible adult kidney transplant recipients at the University of Kansas Kidney Transplant Clinic. Eligible patients who attended the clinic between May 2015 and June 2016 were approached to participate in the study. To minimize the acute effect of high dose steroids, surgery, and possible post-operative complications, cognitive assessments were conducted only after the patient was at least one month post-transplant. Cognition was assessed during the clinic visit for post-transplant care.

The Montreal Cognitive Assessment (MoCA) was used to assess cognition. The MoCA is a validated, clinic-based tool that samples from various domains of cognition. The researchers used the MoCA due to its focus on executive function, a domain more commonly affected in kidney disease. The MoCA consists of a single page and can be completed in less than 10 minutes. The original English version was used.

Of the 297 eligible patients approached for the MoCA test, 265 met inclusion criteria and completed the MoCA. Of those, 226 had complete data and were included in the analysis. Mean age of the 226 participants was 54 years, 39% (n=89) were female, 73% (n=173) were white, and 58% (n=130) had an education level of college or above. Approximately half were obese (n=115), with a body mass index (BMI) ≥30 kg/m2; mean estimated glomerular filtration rate (eGFR) was 52 mL/min/1.73 m2. Average time on dialysis prior to transplant was 2.3 years and average time since transplant was 3.4 years. Three percent of the participants had a history of stroke and 21% had a history of coronary artery disease.

Results of the MoCA found that 58% reached criteria for cognitive impairment. Mean age was higher among those with cognitive impairment compared with those without cognitive impairment (P<.001) and a lower proportion of female participants had cognitive impairment (P=.02). There were no differences between those with cognitive impairment and those without cognitive impairment based on race, level of education, time since transplantation, time on dialysis prior to transplantation, and a history of smoking, coronary artery disease, atrial fibrillation, diabetes, or cause of end-stage renal disease (ESRD).

In bivariate analysis, there was an association between higher MoCA scores and lower age (P<.001), female gender (P<.001), lower levels of serum hemoglobin (P=.015), and higher level of education (P=.003). Factors not associated with MoCA score were race, BMI, blood pressure, eGFR, time since kidney transplantation, history of smoking, stroke, diabetes, coronary artery disease, atrial fibrillation, and ESRD secondary to diabetes. In multivariable analysis, there was an association between higher MoCA score and younger age, female gender, a higher level of education, and diabetic status.

In logistic regression analysis, older age was associated with higher risk for cognitive impairment. The researchers also analyzed the prevalence of cognitive impairment stratified by 5-year age groups; the results showed an increased prevalence of cognitive impairment with older age, but also a high prevalence of cognitive impairment even in patients <50 years of age.

There were some study limitations cited by the authors, including the cross-sectional design that precluded conclusions regarding cause and effect and provided no information on whether cognitive impairment was worsening, improving, or stable; excluding patients who did not speak English may have limited the generalizability of the findings; not assessing depression in the study; and obtaining the clinical data from chart review.

“The prevalence of cognitive impairment in kidney transplant recipients is high. In contrast to the general population even younger transplant recipients have a high prevalence of cognitive impairment. This information should be taken into consideration during patient education and monitoring of medical adherence. Further research is needed to understand the pathophysiology and consequences of cognitive impairment in transplant recipients. Strategies to help kidney transplant recipients cope with cognitive deficits should be developed,” the researchers said.

Takeaway Points

  1. Among 226 participants in a study to assess the prevalence of cognitive impairment among kidney transplant recipients, the prevalence of cognitive impairment was 58%, based on scores on the Montreal Cognitive Assessment (MoCA).
  2. In multivariable analysis, there was an association between lower scores on the MoCA and older age, male gender, and absence of diabetes.
  3. There was an increased prevalence of cognitive impairment with older age among kidney transplant recipients, but also a high prevalence of cognitive impairment even in individuals <50 years of age in that patient population.