‘Brain Fog’

The impact of Covid-19 on our lives has been immense – it continues to be hugely important though the intensity of interest and fear associated with the daily TV communications about it in the early days of 2020 has subsided.


A report this week drew attention to the long term effects on some people: the strange phenomenon of Long Covid includes greater risk of ‘Brain Fog’ and dementia Covid linked to longer-term elevated risk of brain fog and dementia | Coronavirus | The Guardian

The newspaper report draws on a scholarly article in the Lancet: Neurological and psychiatric risk trajectories after SARS-CoV-2 infection: an analysis of 2-year retrospective cohort studies including 1 284 437 patients - The Lancet Psychiatry


This reviewed the health and mortality of 1,487,712 people from electronic health records from the USA and a number of other countries, including the UK, who have experienced infection with Covid-19 in one of its variants. Their subsequent experience of morbidity with a number of conditions was compared with that of people who had experienced a respiratory infection not-covid, over a follow up of 800 days.


The analysis differentiates by age group: children (<18 years), adults (18-64) and older adults (65+).


The conditions included: mood disorder, myoneural junction or muscle disease, dementia, anxiety disorder, cognitive deficit, encephalitis, epilepsy or seizures, Guillain-Barre syndrome, insomnia, intracranial haemorrhage, ischaemic stroke, nerve, nerve root and plexus disorder, Parkinsonism, psychotic disorder, and ‘any first outcome’.


For most of these, there was no difference in incidence between the covid cases and controls. There is marked divergence for the muscle disorders – but these affect less than 0.5% over the two years. There are more diagnoses of dementia in the covid cohort, but affecting less than 1% in this time frame. There are more cases of ‘cognitive deficit’ in the covid group – affecting up to 8% of the cohort.


For the headlines, and in the Lancet paper, ‘cognitive disorder’ is otherwise termed ‘brain fog’. This is not a phenomenon I have recognised, but there it is in a most respected medical journal. What is it and what are its implications for future mental health?


I find that it is a term which began to appear in dictionaries and papers from 2000 onwards as an equivalent to ‘clouding of consciousness’ which is a term we have been used to, but which has always been difficult to define. ‘Brian fog’ has been used quite often in papers about covid – to capture the variable grasp and impaired concentration which people often describe in the periods after the acute infection and may persist for a long time, often associated with lack of energy, a feeling of tiredness and lethargy, a loss of enthusiasm.

Before covid, and since, it has been described amongst people suffering from auto-immune diseases and other chronic illness.


In old-fashioned money I would say it is equivalent to an attenuated subacute delirium. This with the confirmation of an increased incidence of dementia in covid cases, confirms that the covid-induced psycho-syndromes are essentially organic psych-syndromes: mood disorder and anxiety may be prominent early on but fall away quite quickly and are not more evident than in controls. Psychoses look to be a little increased, but at less than 0.6%.


The worry is that this ongoing subacute delirium represents an effect of ongoing, grumbling, unresolved physical consequences of the infection, which may be still active years after the original attack. What is a subacute delirium now may become an established and progressive dementia in the future.


Best strategy has to be prevention of covid if at all possible. What can be done to eradicate these lingering effects of its presence must be subject of research.



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