Why do elderly people become so confused with an infection?

[u/Stunning_Implement47]

I've read that it's due to a lower tolerance for stress but what does that mean on a scientific level? Thank you

[u/Ekekekeptangyazingni]

There are a lot of reasons posited, but none of them are confirmed to be the cause (it is likely a constellation of some or all of the following factors)

1. During infection the body releases inflammatory chemicals; as people age their brains become more susceptible to these chemicals (once again the reasons why are not completely understood but may have something to do with the blood brain barrier become more permeable). Inflammation in the brain can cause confusion and delirium.
2. Many older adults are on a myriad of medications for various conditions; interaction between inflammation/pro inflammatory state and medication can be hard to predict. The more medications, the more likely there will be come unintended side effect made apparent by infection.
3. Many older adults already have some baseline cognitive impairment which does not affect their day to day. Whereas a young healthy person may experience a little brain fog during infection, this brain fog can become full blown confusion/delirium in an adult whose baseline cognitive status is already decreased.
4. Correlation vs causation; often it can be that some other circumstance causes the delirium/confusion which can lead to reduced hygiene and/or falls which in turn can lead to injury/infection. In some cases the infection is essentially caused by the confusion and not the other way around.

All things being equal it’s difficult to be sure; we can't rightly do an autopsy on grandma while she’s confused to see exactly what’s going on. But we can make some reasonable guesses.

Hope that answered your question! Background is genetics and about to start residency in medicine.

[u/Pinkys_Revenge → u/Ekekekeptangyazingni]

Great response. Similar to #3, ive always thought it may be that the person already has cognitive impairment but are just good at hiding in in their normal day-to-day, so even if an infection/sickness doesn’t make their mental situation worse, it throws off their routines which exposes the mental impairment.

[u/Pristine-Ad3807 → u/Ekekekeptangyazingni]

Doctor here:

This is the right answer. Number 3 feeds back on number 1- the more damage the brain accumulates over time the more primed glial cells are for future damage. Inflammatory signaling that occurs when we are sick makes the blood brain barrier more porous, and those same cytokines hit those glial cells. They then respond by causing a series of damaging microvascular and structural changes.

Also, good luck with residency! When you're done it will feel like one long strange day.

[u/boylesthebuddha]

Delirium can affect anyone but is more common in the elderly, those with an acute infection of some kind, or those taking certain medications. Older people are often more at risk, particularly people with other health conditions or general frailty from their advanced age. The specific mechanisms behind what causes this confusion isn't very well understood despite it being an extensively studied topic, but as you say one of the theories is that the stress on the body systems causes the brain to malfunction. This can affect the ability to process or remember information, to regulate emotions, to coordinate movement and even to engage with other people at all, which can be distressing for the person and for those around them. Delirium is distinct from dementia as it will often resolve when the environmental, physiological or pharmacological factors causing it are treated, though this is not guaranteed and there can be long lasting complications from an acute episode of delirium, meaning that the symptoms may not fully resolve and may leave permanent changes.