Brain Fog and Kidney Disease?



Brain Fog.  It’s often a hot topic in kidney patient forums across many patient profiles and for a variety of clinical subtypes, regardless of patient age or ethnicity. Usually it appears online as a group of concerns regarding memory issues, lack of ability to focus, and a general feeling of confusion or lack of mental clarity.  While ‘brain fog’ isn’t a medical term, that phase certainly paints an appropriate word picture to describe how some kidney patients feel when that wide range of symptoms affects their daily routines in life.

Just as with the general public, patients with kidney disease or chronic illness can experience trouble concentrating or may have episodes of forgetfulness.  Difficulty with gathering and processing information (among other cognitive functions) can impact students at school or may challenge employees in the workplace.  For patients with kidney disease, confusion or memory issues regarding appointments or medication routines may interfere with patient compliance related to medical care. It’s vitally important to note that at times all people can experience degrees of forgetfulness or have periods in which lack of concentration or attention might cause personal, work, or health issues – or vice versa.   Stress, diet, lack of sleep, certain medications, and various medical conditions may all affect mental clarity or how individuals take in and process information about the world around them.

From various journal articles on this topic, it appears that even moderate forms of chronic kidney disease (CKD) may cause issues with cognitive function, and that this impact may be more pronounced for patients with end stage renal disease (ESRD), to include dialysis patients or as well as those who have had a kidney transplant.    Atypical HUS is a very rare disease, affecting an estimated 1 to 2 patients per million people.  With 20% of aHUS patients noted to have no kidney involvement (Yao et al, 2015), it would appear that 80% of aHUS patients have some sort of kidney damage or injury at initial presentation or during disease activity.  According to Ažukaitis K et al in 2014, an estimated one-fifth of aHUS patients have organs or body systems other than the kidneys impacted (extra renal involvement), most often involving the myocardium (middle layer of the heart) and the central nervous system (CNS, to include the brain).   Atypical HUS patients sometimes mention fatigue, headaches, or mood changes such as anxiety in conjunction with a targeted focus:  concerns about a perceived decline in memory, reasoning or attention.

For adults living with aHUS and for caregivers of pediatric patients, we present here a few research links to provide background information regarding whether vague feelings of ‘brain fog’ might have an actual basis in kidney function issue.  Knowledge is power, so learn more on this topic to translate concerns  into an action plan so that you can begin an informed discussion with your aHUS care team about mental confusion, memory struggles, and difficulty with new situations or information.

(Our Note:  Links are to Full Text, if available to the public. For research links to abstracts, we suggest checking with your physician to request a Full Text print copy.)


Kidney Disease and Cognitive Function  (Elias M et al, 2013)

“In each, CKD is related to a wide range of deficits in cognitive functioning including, verbal and visual-memory and organization, and components of executive functioning and fluid intellect.”

“In summary, community-based, large sample, cross-sectional studies support the generalization that mild and modest kidney disease is related to modest deficits in multiple cognitive abilities.”

“One may hypothesize, among other models, direct paths in which CKD affects brain function and morphology and hence cognition. An alternative, and not mutually exclusive, possibility is that risk factors shared by brain and kidney lead to cognitive deficit, decline and impairment .”

Note from the aHUS Alliance:  Learn about  executive functioning and fluid intellect.



Neurological complications in chronic kidney disease   (Arnold R et al, 2016)

“Common neurological complications in CKD include stroke, cognitive dysfunction, encephalopathy, peripheral and autonomic neuropathies.”

“Neurological complications often become clinically apparent at end-stage disease, however early detection and management of these conditions in mild CKD may reduce their impact at later stages.”

“While cognitive impairment is recognised as a common complication of CKD, it remains poorly identified. The reported prevalence of cognitive impairment in dialysis is estimated at between 30% and 60% while less than 5% of patients have clinically documented histories of cognitive impairment.  Evidence suggests that both the prevalence and progression of cognitive impairment are inversely associated with the level of kidney function. Several large population-based studies have demonstrated an increased risk of cognitive decline in the presence of moderate CKD including an 11% increased prevalence of cognitive impairment per 10 mL/min/1.73 m2 decrease in eGFR.”



Cognitive alterations in chronic kidney disease: an update   (Mendonça da Matta S et al, 2014)

“Impairment of cognitive functions occurs frequently in chronic kidney disease (CKD)”

“The neuropsychological performance improves with the initiation of dialysis, although some cognitive dysfunctions remain even after treatment, especially in the areas of attention, cognitive flexibility, memory and learning. Kidney transplantation may improve and even reverse some cognitive deficits detected in the dialysis period, despite some compromise in verbal memory and executive functions remain after transplantation.”



Cognitive Impairment in Peritoneal Dialysis Patients  (Kalirao P et al, 2012)

“Prevalence of moderate to severe cognitive impairment among hemodialysis patients is more than double the prevalence in the general population. This study describes cognitive impairment occurrence in a peritoneal dialysis cohort compared with a cohort without chronic kidney disease (CKD).”

“Of the peritoneal dialysis cohort, 33.3% had no or mild, 35.3% moderate, and 31.4% severe cognitive impairment; corresponding values were 60.4%, 26.7%, and 12.9% of the non-CKD cohort, and 26.6%, 36.4%, and 37.0% of the hemodialysis cohort.”



Cognitive impairment in hemodialysis patients is common   (Murray AM et al 2006) 

“Hemodialysis patients are at high risk for cognitive impairment due to their older age and high prevalence of stroke and cardiovascular risk factors.”

“Of 338 subjects who completed testing in at least two of the three cognitive domains, 13.9% (95% CI 10.4, 18.1) were classified with mild impairment, 36.1% (31.0, 41.5) with moderate impairment, 37.3% (32.1, 42.7) with severe impairment, and 12.7% (9.4, 16.8) with normal cognition.”

“Moderate to severe cognitive impairment is common and undiagnosed in hemodialysis patients. Further studies are needed to determine whether dialysis exacerbates the cognitive impairment attributable to underlying disease. Cognitive testing in hemodialysis patients before dialysis initiation and periodically may be warranted.”



Cognitive remediation in pediatric CKD and ESRD: rationale, candidate interventions, and applicability  (Javalkar K et al, 25 Feb 2017)

“The purpose of this paper is to address the potential use of cognitive remediation interventions for children and adolescents with chronic kidney disease (CKD) and end-stage kidney disease (ESKD). The prevalence and risk for neurocognitive dysfunction in children with this condition remains high, but, to date, interventions targeting these challenges have not been attempted either individually or as part of a larger treatment program. This is the next logical step in addressing the neurocognitive dysfunction that can be present in pediatric CKD/ESKD, with the field needing to determine the efficacy of cognitive remediation approaches for this population. To our knowledge, this paper is the first to raise this possibility by identifying candidate treatments addressing the neurocognitive challenges observed in children and adolescents with CKD/ESKD.”



Memory and Executive Functions in Pediatric Chronic Kidney Disease  (Gipson D et al, 2007)

“This study examined the memory and executive functioning of children and adolescents with chronic kidney disease (CKD). The sample included 20 children and adolescents with CKD ranging in age from 7.50 to 19.04 years (M = 13.41, SD = 3.20). Intellectual function for the group was within the low average to average range (M = 89.32, SD = 14.80). Of the participants with CKD, 12 were receiving maintenance dialysis therapy at the time of testing and 8 were managed with conservative therapy.”

“In all instances the CKD group performed lower than the typical group. The CKD group was particularly deficient in their initiation behaviors within the executive function domain. The groups did not differ on Set-Shifting or Inhibition. These findings remained present even when IQ and chronological age were controlled in the analyses, suggesting the possibility of specific encroachment of renal disease on memory and executive functions beyond the generalized effects of lower IQ. This study represents one of the most extensive examinations of memory and executive functions that has been conducted to date on children and adolescents with CKD. While pervasive dysfunction was not apparent in the children with CKD, they clearly appeared to be at risk for lower IQ as well as inefficiencies in key neurocognitive domains.”



Cognitive Improvement in Children with CKD after Transplant  (Icard P et al, 2010)

“Children with end-stage kidney disease (ESKD) requiring dialysis and subsequent transplantation are at risk for neurodevelopmental delays and deficits. Lower scores on measures of IQ and academic achievement, as well as in specific cognitive domains of language, visual-spatial perception, attention, memory, and executive function have been documented by previous research.”

“Although a relatively small sample was examined, this one of only a few studies which examined the impact of kidney transplant on developmental and intellectual functioning in children. In general, findings from this study suggest that children with CKD receiving transplant evidenced significant improvement in their overall cognitive function after transplant.”



Beneficial effect of renal transplantation on cognitive brain function  (Kramer L et al, 1996)

“Cognitive brain dysfunction is a common complication of end-stage renal disease.”

“Our findings indicate that cognitive brain dysfunction in hemodialysis patients may be fully reversed by successful renal transplantion.”



Cognitive functioning pre- to post-kidney transplantation—a prospective study  (Griva K et al, 2006)

“Kidney transplantation (TX) may ameliorate the neuropsychological (NP) impairments in end-stage renal disease (ESRD).”

“Within-subject comparisons showed statistically significant improvement in memory performance after kidney TX. Other NP measures (attention–concentration and psychomotor abilities) showed non-significant improvements. Normative comparisons showed NP impairments on dialysis, which were not apparent after TX.  Conclusion. These data demonstrate improvements in cognition following kidney TX and emphasize the reversibility of the memory problems evidenced in dialysis.”