Cognition in chronic kidney disease: a systematic review and meta-analysis
Cognitive impairment is cognitive decline greater than expected with normal ageing but which does not interfere notably with activities of daily living. Poor cognitive function has been linked to poor health literacy, poorer medication adherence, worse physical and mental health, and greater morbidity and mortality. Chronic kidney disease (CKD) may be an independent risk factor for cognitive impairment. A recent systematic review by Etgen et al. [1] found that, in cross-sectional and longitudinal studies, cognitive impairment and incident cognitive impairment, respectively, were more common in CKD patients compared to people without CKD. Heterogeneity between studies was high, and age and sex were significant contributors. Six cross-sectional and six longitudinal studies could be included in their meta-analysis. While there were few included studies, there was no evidence of publication bias, and their data suggest that lower estimated glomerular filtration rate (eGFR) may be associated with greater incidence of cognitive impairment [1]. Although the economic burden of mild cognitive impairment and CKD-related cognitive changes is poorly understood, the cost of dementia has been studied in detail. Lower neuropsychological test scores are associated with increased social and financial costs, including caregiver burden [2–4].
In clinical practice, screening for or monitoring of cognitive impairment relies on the use of cognitive tests. For many clinicians, ease of use and quick administration of cognitive tests may be particularly important. Brief cognitive screening tests, such as the Mini-Mental State Examination (MMSE), have been popular as a result [5]. However, general screening tools may not differentiate specific aspects of cognition that are most affected. Cognition is classified into several discrete domains, encompassing such diverse processes as visuo-spatial perception, auditory memory, visual memory, attention span, motor function, and mathematical reasoning.
The pattern of cognitive impairment in CKD is not clear. With dialysis, CKD-related cognitive impairment is at least partially reversible (with the domains of Orientation Attention and Memory showing significant improvement), and all domains show improvement with renal transplantation [6, 7]. It is important to understand the pattern of cognitive impairment in CKD to distinguish it from neurodegenerative diseases, stroke and traumatic brain injury, which can co-exist with CKD, may be related to the aetiology of particular patients’ kidney disease, and may be treatable if properly diagnosed. Unlike CKD-related cognitive impairment, these conditions tend to present as acute events with significant deficits specific to the anatomy affected and which may be amenable to specific cognitive or occupational therapies aimed at enhancing function rather than reversing the cause [8–10]. CKD patients are at higher risk than the general population for stroke, and the likelihood of stroke increases with falling eGFR [11]. Nevertheless, CKD-related cognitive impairment can also be severe, and patients may become unable to make healthcare decisions [12]. Identifying the pattern of CKD-related cognitive impairment enables two steps toward improving care for CKD patients. Firstly, by specifying the phenomenon under investigation, it may bring us closer to identifying potential mechanisms, anatomical areas affected, and treatments. Secondly, by identifying CKD-related deficits, it may enable recommendations for shared decision-making, advance care planning, and addressing self-management challenges related to the complex care needs of CKD patients before their decision-making capacity diminishes.
We aimed to systematically review patterns of cognitive impairment in CKD, specifically the cognitive domains most affected, and to investigate any change with declining kidney function.