A 68-year-old woman with a history of well-controlled hypertension and diabetes presents to the office for routine follow-up. She says she has adhered to her current medications, and her blood pressure and hemoglobin A1c remain at goal. At the close of the visit, she mentions that she is worried she may be developing dementia. She says she has been having difficulty finding the right word in conversation and needs to write things down more than she used to.
What might be causing this patient’s changes in cognition?
In primary care settings, when patients complain of memory loss, there is a 20% to 30% chance they will be found to have mild cognitive impairment (MCI) or some level of dementia.1 Given the significant consequences of dementia, it’s important to maximize opportunities to distinguish those with age-related changes in cognition or reversible causes of memory loss from those who have irreversible pathologic changes.
Age-related changes in cognition
Changes in cognition associated with aging vary considerably among individuals and across domains of cognition. By their 7th decade, most people experience a decline in processing speed and working memory.2 However, some individuals retain excellent function into their 80s and perform as well as younger adults.3
Changes long thought to be due to brain senescence may, in fact, be related to the effects of age-related medical conditions on the brain’s function.4 Consistent with this theory is the observation that cognitive changes tend to occur earlier in individuals with cardiovascular disease, diabetes, and cancer.2 What constitutes a normal change depends on an individual’s baseline cognitive function, educational background, medical comorbidities, and the potential impact of sensory impairment on performance.
General cognitive trends with aging. Awareness of normal changes in an aging population is useful when assessing patients concerned about their memory. In general, an individual’s ability to maintain attention to a single task is preserved into late life. Ability to perform tasks requiring divided attention or attention-switching tends to decline.3 This has implications for driving, given the need to constantly switch one’s attention in response to the environment and the ability to sort relevant from irrelevant information.
Remote memory, semantic memory (factual information), and procedural memory (knowledge of skills and procedures) tend to remain intact with aging.4 Short-term memory (simple maintenance of information over a short period of time) shows little change with aging. However, working memory, which requires the manipulation of information in short-term memory, declines.
A simple demonstration of this is that performance on digit span testing tends to remain preserved (7±2), but digit span backwards declines. Holding digits in mind in the order they are received can be achieved through rehearsal. But to reverse the order requires reorganization of the information, and this ability declines with aging.3
Prospective memory (remembering to do things in the future) often requires increased dependence on external aids, such as a to-do list.3 The capacity to learn and recall new information declines. Even when given repeated opportunity to practice, older adults demonstrate a slower learning curve and lower total amount learned.4 Therefore, it becomes easier relying on well-learned cognitive processes such as cooking a familiar meal or relying on previously used principles for decision making.2
Language comprehension and vocabulary remain stable over time. However, difficulty with spontaneous word finding—the “tip-of-the-tongue” phenomenon—tends to increase. In contrast to the dysnomia related to dementia, the word-finding difficulties with normal aging typically improve with cues, indicating that the problem is in retrieval of information rather than storage. Verbal fluency, the rate at which words from a single category can be produced, shows decline. This is particularly true in tests of semantic verbal fluency (name all the animals you can think of); phonemic fluency (words that start with a certain letter) tends to be preserved.4
Some studies using neurocognitive testing have suggested a decline in executive functioning. But, in general, aging has little impact on “real world” executive functions that are required for planning and executing tasks.4 On the whole, cognitive changes related to aging typically do not interfere with an individual’s ability to function independently.
Mild cognitive impairment/mild neurocognitive disorder
Originally conceived as a precursor to Alzheimer’s dementia,5 mild cognitive impairment (MCI) is a diagnosis that has evolved to describe a heterogeneous syndrome of abnormal cognition characterized by:6-8
- a suspected change in cognition expressed by the patient, an acquaintance who knows the patient well, or a clinician;
- objectively measured impairment in one or more cognitive domains beyond what would be expected based on an individual’s age and educational background;
- preservation of functional abilities; and
- a lack of findings that would fulfill criteria for dementia.