Dr Kevin McCarroll
Medical Matters
Memory decline is common in older age and indeed about 20% of adults over 65 have some degree of clinically significant cognitive impairment. Notably, the incidence of dementia also doubles every 5 years from the age of 65 reaching a prevalence of about 20% by the time one achieves octogenarian status! Despite the rising number of dementia cases, there is some good news in that the age at which it develops appears to have increased in the last decade.
Unfortunately, even with healthy ageing comes the inexorable death of brain cells and by as early as midlife, subtle changes in cognitive function are detected. In some cases, the brain may shrink by as much as 5% per decade after the age of 40 with a loss of both grey and white matter. Studies suggest that this shrinkage is not uniform and may be more marked in part of the frontal lobe that is important for attentional processing and problem solving. However, this does not usually impact in any significant way in gross cognitive ability.
In clinical practice, it’s common to see variable degrees of brain shrinkage on neuro-imaging in people of the same age and in the absence of dementia. Several factors such as genetics, lifestyle (alcohol intake and possibly smoking) and other vascular risk factors like high blood pressure may influence this. Diabetes, smoking and hypertension also contribute to hardening of the arteries in the brain reducing or blocking blood flow in the smaller vessels and causing micro-areas of brain damage. Indeed, these appear as small spots on brain scans, usually occur without any symptoms and as they accumulate can result in increasing cognitive impairment.
Worried
But when should you be worried about your memory? Firstly, for some patients, subjective memory complaints are nothing to worry about and can occur in healthy normal people. For example, absent mindedness doesn’t usually reflect anything serious and simply results in a lack of focus and attention. Several factors can impair attention like tiredness, poor sleep, low mood and worry or anxiety can also lead to distractibility and lack of focus too. This will both impair the efficient pick of information but also its retrieval – we all have encountered times when we’ve been stuck for a word or name, or lose our train of thought mid-sentence! Certain medical conditions like an underactive thyroid gland can also give a similar pattern of cognitive dysfunction as can mild to moderate vascular disease in the brain. Some medications can also affect memory and may need to be changed.
On the other hand, concerning features for Alzheimer’s include progressive cognitive decline, persistent loss of memory for new things and often problems with word finding and naming. Damage to the hippocampus which is the brain structure that stores new memories occurs early in Alzheimer’s resulting in impaired retention of new information. Over time, nothing new can be retained with patients often repeating themselves and having no recognition even when reminded. As the disease spreads to other brain areas, it affects problem solving and judgement and eventually leads to global cognitive impairment.
However, early in the course of Alzheimer’s general day to day function is preserved and the diagnosis is difficult to make. In fact, the term dementia is only applied when a medical condition causes sufficient cognitive impairment to impact on the usual activities of daily living. In practice, Alzheimer’s is only reliably diagnosed when it progresses to the early stages of dementia.
The term ‘mild cognitive impairment’ also denotes a problem with your memory in the absence of dementia, but has an annual rate of transition to dementia of about 15%. Mini-stroke disease and other conditions may result in stable cognitive impairment but don’t have the classical hallmark of rapid forgetfulness as occurs in Alzheimer’s.
In about 30% of cases, dementia has other causes including stroke and some neurodegenerative conditions. For example, Parkinson signs with dementia suggests Lewy Body dementia or Progressive Supranuclear Palsy. Prominent personality changes, apathy and disinhibited behaviour at an early stage suggest frontotemporal dementia. Still another type of dementia called Primary Progressive Aphasia results mainly in language difficulties. And there are even very rare causes that result from autoimmune conditions where the body attacks the brain but can be halted with drugs.
Despite this, Alzheimer’s makes up the bulk of cases for which there are currently two medications available. Both work to improve neurotransmitter imbalances in the brain, though their effect on cognitive performance is modest and not everyone benefits. In recent years, what has become clear though are some of the main risk factors for Alzheimer’s. These include high blood pressure, diabetes, smoking, obesity, higher alcohol intake and lower education status. If these are addressed from midlife, Alzheimer’s risk may be reduced by as much as 40%.
If you have persistent memory problems, do make sure to go your GP and get checked out – as there are things that can be done that may help.