What conditions affect mental capacity?

Any disorder of the mind or brain causing confusion or disordered thinking can impair mental capacity. It may be affected temporarily or permanently depending on the cause. As already mentioned, capacity is decision and time specific meaning that it can fluctuate, and that a person may lack capacity for one decision but not for others.

Dementia is an important cause of impaired mental capacity in older people as dementia primarily affects older people, although early - onset dementia also exists. Since we are living longer, its prevalence is increasing. Dementia is an umbrella term for degeneration of the brain from different causes; these in turn make up the different types of dementia. This will be the subject of a future blog post.

Other causes of a lack of mental capacity include comatose states (from any cause), head injuries, brain tumours, strokes and infections of the brain.

Another important cause of impaired mental capacity that I see frequently in hospital practice is delirium. It is often confused for dementia but the 2 conditions present differently with delirium having a more abrupt onset than dementia, and being either hypoactive or hyperactive. Delirium and dementia often coexist as people with dementia have ‘vulnerable’ brains making them more prone to delirium.

In older people delirium has myriad causes, the most common of which are infections including UTIs, medication side effects, electrolyte disturbances such as low sodium, dehydration, and even constipation. Whilst delirium is often temporary unlike dementia it can persist for several months and can contribute to permanent cognitive impairment.