Kidney Matters - Issue 17 Summer 2022

10
Kidney Clinic
‘Kidney brain’: cutting through the fog
Brain fog or cognitive impairment is
common among people with chronic
kidney disease (CKD). Why does it
happen? And how can it be improved?
Although people with CKD commonly report some
kind of brain fog or cognitive impairment, it is difficult
to know precisely how many people are affected.
Estimates vary widely, but one study from the US
suggested that as many as 8 in 10 (80%) of people
with kidney failure needing treatment with dialysis had
some degree of cognitive impairment.
What is cognitive impairment?
Cognitive function is a general term covering several
domains or tasks performed by the brain (see Table 1).
The degree of impairment varies greatly, but studies
show that executive function is the most commonly
affected domain in people with kidney disease.
Professor Paddy Mark comments: “Cognitive
impairment sounds alarming, but it is important to
differentiate between impairment in general—which
may be permanent or a sign that someone is acutely
unwell and resolves after they get better—and brain
fog that happens on dialysis.” Paddy is Professor of
Nephrology and Honorary Consultant Nephrologist at
the Glasgow Renal and Transplant Unit at the Queen
Elizabeth University Hospital Glasgow. He has a special
research interest in vascular disease in CKD.
What are the risk factors for brain fog?
Several ‘traditional’ factors are known increase the risk
of cognitive impairment (Table 2). Age is the greatest
risk factor in the general population, doubling for
each 10 years over the age of 60 so that some degree
of cognitive impairment affects about 1 in 4 people
aged over 80 years. Vascular disease, diabetes and
high blood pressure all increase the risk of cognitive
impairment by affecting the small blood vessels of the
brain, while depression and poor sleep both impair
cognitive functioning.
Paddy says: “Older age is also a risk factor for CKD, and
many people who start dialysis have other medical
problems. For example, they almost certainly have
high blood pressure, and diabetes is the commonest
cause of CKD in the UK, being present in up to one
third of people needing kidney replacement therapy.
“A large study in Sweden showed that, as kidney
function declines, the number people diagnosed with
Table 1: Domains of cognitive function
Domain
Memory and learning
Language
Executive function
Complex attention
Social cognition
Visuospatial perception
Description
Recording and retrieving information such as facts and events
Naming objects, finding one’s words, understanding the meaning of words
Planning, making decisions, carrying out and prioritising complex tasks
Staying focused, especially when there are distractions
Recognising emotions, empathising with others’ emotions
Recognising and manipulating objects, co-ordinating physical actions
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