Although dementia does not indicate a particular disease, certain combinations of symptoms and neurologic signs are more or less characteristic and aid greatly in diagnosis. The age of the patient, the mode of onset of the dementia, its clinical course and time span, any associated neurologic signs, and accessory laboratory data constitute the basis for differential diagnosis. It must be acknowledged, however, that some of the rarer types of degenerative brain disease are at present recognized mainly by pathologic examination or genetic testing. The correct diagnosis of treatable forms of dementia—subdural hematoma, certain brain tumors, chronic drug intoxication, normal-pressure hydrocephalus, HIV (reversible to some extent), neurosyphilis, cryptococcosis, pellagra, vitamin B12 and thiamine deficiency states, hypothyroidism, and other metabolic and endocrine disorders—is, of course, of greater practical importance than the diagnosis of the untreatable ones. Also important is the detection of a depressive illness, which may masquerade as dementia, and chronic intoxication with drugs or chemical agents, both of which are treatable. Also, progressive deafness or loss of sight in an elderly person may sometimes be misinterpreted as dementia. In the future, when effective means for treatment of degenerative dementias are established, refined methods, mentioned further on, will be used to differentiate the fundamental causes of neuronal damage.
The first task in dealing with this class of patients is to verify the presence of intellectual deterioration and personality change. It may be necessary to examine the patient serially before one is confident of the clinical findings and their chronicity. A mild aphasia from a focal brain lesion should not be mistaken for dementia. Aphasic patients appear uncertain of themselves, and their speech may be incoherent. Careful attention to the patient’s language performance will lead to the correct diagnosis in most instances. The abrupt onset of mental symptoms usually points to a delirium or other type of acute confusional state or to a stroke; inattention, perceptual disturbances, and often drowsiness are conjoined (see Chap. 19).
There is always a tendency to assume that mental function is normal if a patient complains only of anxiety, fatigue, insomnia, or vague somatic symptoms, and to label the patient as anxious. This will be avoided if one keeps in mind that these psychiatric disorders rarely have their onset in middle or late adult life.
Clues to the diagnosis of depression are the presence of frequent sighing, crying, loss of energy, psychomotor underactivity or its opposite, agitation with pacing, persecutory delusions, hypochondriasis, and a history of depression in the past and in the family. Although depressed patients may complain of memory failure, scrutiny of their complaints will show that they can usually remember the details of their illness and that little or no qualitative change in other intellectual functions has taken place. Their difficulty is either a lack of energy and interest or preoccupation with personal worries and anxiety, which prevents the focusing of attention on anything except their own problems. Even during mental tests, their performance may be impaired by “emotional blocking,” in much the same way as the worried student blocks during an examination. When such patients are calmed by reassurance and encouraged to try harder, their mental function improves, indicating that intellectual deterioration has not occurred. Conversely, it is helpful to remember that demented patients in the mid-stages of the process infrequently have sufficient insight to complain of mental deterioration; if they admit to poor memory, they do so without conviction or full appreciation of the degree of their disability. The physician must not rely on the patient’s statements alone in gauging the efficiency of mental function and should seek corroboration from family members. Yet another problem is that of the impulsive, cantankerous, and quarrelsome patient who is a constant source of distress to employer and family. Such changes in personality and behavior (as, e.g., in Huntington disease) may precede or mask early intellectual deterioration.