In the following pages, we consider the prototypic dementing syndromes. As has been emphasized, they are most frequently due to degenerative diseases of the brain (see Chap. 38) and less often occur as a component of other categories of disease (vascular, traumatic, infectious, demyelinating), which are considered in their appropriate chapters. The discussion of dementing diseases is preceded by a description of a syndrome of incipient dementia currently called mild cognitive impairment.
It has become apparent that many individuals have memory complaints that are mild and do not interfere with daily functioning but are still disproportionate for the patient’s age and education. It is often difficult to differentiate this very troubling but less-intrusive problem, which may be a result of the normal process of aging, from dementia. The condition has been called mild cognitive impairment, and in the past, age-associated memory impairment, or benign senescent forgetfulness, as discussed in Chap. 28. When other aspects of mental functioning are affected, terms such as aging-associated cognitive decline had been used. Defining the boundaries of such a condition has proved problematic, and determining the risk of progression to a dementing illness that does interfere with daily function, even more so. There is a further problem introduced by the premise that highly intelligent individuals would have to decline considerably on intelligence and memory tests to be identified as being below certain age-adjusted norms. However, a notion has evolved in which Alzheimer disease and mild cognitive impairment exist in a spectrum (see Petersen), and one of the main values to identifying such patients in a presymptomatic period of Alzheimer disease is the potential for early institution of treatment.
It must be stated, however, that worry over occasionally forgetting one’s keys or recalling another person’s name as one ages, common complaints in the neurology practice setting, generally do not indicate cognitive decline, mild or otherwise. Many factors including poor sleep and sleep apnea, depression, medications, systemic endocrine and infectious disorders, and general distractibility contribute greatly to these complaints in the normal population.
In most studies, 10 to 20 percent per year of such affected patients with mild cognitive decline will be found to have later acquired Alzheimer disease. A number of factors have been identified as associated with a progression to a state of indisputable dementia. These include elevated blood pressure, changes in the cerebral white matter on MRI, abnormality of gait, and—perhaps not surprisingly—certain biologic markers that are connected to Alzheimer disease. Other factors for the development of dementia, particularly the level of prior education and maintenance of an active mental life, have been studied in relation to the later development of Alzheimer disease, much of which has reached the popular consciousness in diluted form, and are discussed in Chap. 38.
At the moment, the clinician must simply counsel caution and reassurance in advising patients with mild memory impairment, and exclude treatable causes. Nonetheless, if the symptoms are progressive or begin to interfere in any consistent way with other mental functions or with the performance of daily activities, a dementing illness is likely.
Despite what has been said in the section above, the earliest signs of dementia caused by degenerative disease may be so subtle as to escape the notice of the most discerning physician. An observant relative of the patient or an employer may become aware of a certain lack of initiative or lack of interest in work, a neglect of routine tasks, or an abandonment of pleasurable pursuits. Initially, these changes may be attributed to depression, fatigue, or boredom in retirement. More often, gradual development of forgetfulness is the most prominent early symptom. Proper names are no longer remembered and cannot be recalled with time, to a far greater extent than can be attributed to mild cognitive impairment. Difficulty in balancing a checkbook and making change becomes evident. The purpose of an errand is forgotten, appointments are not kept, and recent conversations or social events have been overlooked. The patient may ask the same question repeatedly over the course of a day, having failed to retain the answers that were previously given.