Changes in Cognitive Function among Patients Undergoing Peritoneal Dialysis

Patients undergoing peritoneal dialysis as home-care therapy are required to self-monitor and self-manage their treatment; effective cognitive functioning is key for this patient population. However, the prevalence of cognitive impairment is high among patients with end-stage renal disease, with estimates of cognitive impairment ranging from 27% to 67%. Previous studies have shown an association between cognitive impairment and mortality and technique failure. Results of an earlier multicenter cross-sectional survey conducted by Yu-hui Zhang, MD, and colleagues among peritoneal dialysis patients found a prevalence of cognitive impairment of 28.4%, assessed using the Modified Mini-Mental State Examination.

Dr. Zhang et al. recently conducted a multicenter prospective cohort study in five provinces in China to examine the risk factors for cognitive impairment in patients undergoing peritoneal dialysis as home care. The study was designed to assess change in cognitive function and the factors associated with the change among peritoneal dialysis patients by measuring cognitive function at baseline and then again after 2 years. Secondary end points were the effects of baseline cognitive impairment on all-cause and cardiovascular mortality, hospitalization, and transition to hemodialysis therapy. Study results were reported in the American Journal of Kidney Diseases [2018;72(5):691-700].

Baseline data were collected from all participants for demographic characteristics, comorbid conditions, and biochemistry indexes. Assessments of cognitive function, depression, and sleep disorders were also made. Participants were followed-up prospectively. Patients who remained on peritoneal therapy between March 2015 and November 2015 underwent repeat measurements of biochemical indexes, cognitive function, depression, and sleep quality.

A total of 667 patients met eligibility requirements; of those, 493 provided participation consent. Baseline and follow-up cognitive testing measurements were available for 458 participants. Participants’ baseline data was comparable to general characteristics of the peritoneal dialysis population in China. Mean age was 51.6 years, peritoneal dialysis therapy duration was 25.1 months, body mass index was 22.9 kg/m2, hemoglobin level was 104.9 g/L, and serum albumin level was 36.2 g/L. Of the 458 participants, 53.1% were men, 23.6% had diabetes mellitus, 21.0% had a history of cardiovascular disease, and 52.4% had a high school diploma or higher level of education.

During follow-up, 165 patients were excluded for various reasons. Reassessment of cognitive function was conducted for the remaining 293 patients. There were no differences in general or specific cognitive parameters between the excluded patients and the remaining patients; diabetes mellitus and serum high-sensitivity C-reactive protein (hs-CRP) were significantly higher in the excluded group compared with the remaining group (P=.006 and P=.004, respectively). There were no other significant differences in demographic or biochemical data between the two groups.

At baseline, 19.7% (n=90) of participants were diagnosed with cognitive impairment; the 90 participants had significantly lower scores on tests of all specific cognitive functions compared with those with normal cognitive function. Compared with the normal cognitive function group, those in the cognitive impairment group were older, less educated, more likely to be female, and more likely to have diabetes mellitus, cardiovascular disease, and higher depression scores. They also tended to have lower serum albumin and calcium levels and higher hs-CRP and total cholesterol levels.

The prevalence of cognitive impairment increased from 19.8% (58/293) to 23.9% (70/293) during follow-up. At the same time, there was significant decrease in Modified Mini-Mental State Examination scores from 94.8 to 83.1 (P=.006). At the 2-year follow-up, the researchers observed better performance on the Trail-A and Trail-B tests that measure processing speed and executive function, and on immediate memory and visuospatial skill tests. There were no significant differences in scores for delayed memory and language ability between baseline and the 2-year follow-up.

There was significant association between advanced age, depression, and lower education level and worsening general cognitive function, and with several measures of specific cognitive function. Advanced age and lower education level were associated with poorer executive function and immediate memory, and depression was associated with impaired memory capacity and language ability.

At the 2-year follow-up, executive function performance tended to be worse among patients with diabetes mellitus . There was significant association between hypoalbuminemia and poorer general cognitive function, delayed memory capacity, visuospatial skills, and language ability. Higher levels of serum sodium contributed to the deterioration in delayed memory capacity and visuospatial skill.

There was no difference in mortality rates between patients with and without cognitive impairment. In univariable analysis, patients with executive dysfunction had an increased risk for all-cause mortality; the increase in risk disappeared following multivariable adjustments. Both global and specific cognitive impairment at baseline were associated with a greater rate of hospitalization. There was an association between memory dysfunction and a lower dialysis modality survival rate.

There were some limitations to the study cited by the researchers, including the relatively small number of deaths, the relatively short observation period, and potential selection bias due to the patients unavailable for the second assessment.

In summary, the researchers said, “The prevalence of cognitive impairment in our study increased over 2 years, although some specific cognitive function improved. In light of the inconsistencies among changes in various cognitive domains noted in our study, future studies exploring changes in both global and specific domains of cognitive function in other ethnic cohorts are warranted. Apart from the well-recognized risk factors for cognitive decline, hypoalbuminemia and depression were also significant risk factors for cognitive decline among peritoneal dialysis patients. Whether correcting these modifiable risk factors would slow down the decline in cognitive function warrants further investigation.”

Takeaway Points

  1. Researchers in China conducted a multicenter prospective cohort study to examine change in cognitive function among patients receiving peritoneal dialysis as home-care therapy; cognitive function was measured at baseline and after 2 years.
  2. Among the 293 patients in the final analysis, the prevalence of cognitive impairments increased from 19.3% to 23.9% during the 2-year study period; however, executive function, immediate memory, and visuospatial skill improved over time.
  3. Advanced age, lower education level, and depression were associated with deterioration in general and specific cognitive function.