Dementias With a Prominent Dysexecutive Syndrome

A second major dementia pattern involves patients who exhibit salient changes in personality and behavior, accompanied by compromised attention, motivation, judgment, insight, and other "executive" functions. This clinical entity has been given several names including frontotemporal dementia (FTD), dementia of the frontal lobe type, and comportmental dementia (30,50,86-88).

In addition, there are overlapping features with the so-called "subcortical dementias" (89,90). This overlap is likely due to the intense connections between the frontal lobes and subcortical regions (91,92), as noted in Figure 2.

A history from a reliable informant often reveals major changes in the patient's personality and social conduct, with inappropriate, embarrassing, or impulsive behaviors. Such disruptions often punctuate behaviors that are otherwise characterized by apathy and withdrawal. Changes in appetitive behavior such as eating or sexual activity are common. Patients tend to present in the presenile years (less than 65 years of age). Mental state examination often reveals compromise of the so-called executive functions, including attention, judgment, and insight. Compared to patients with probable AD, patients with

FRONTAL LOBES «-

STRIATUM (CAUDATE/PUTAMEN)

GLOBUS PALLIDUS/SUBSTANTIA NIGRA

THALAMUS

Fig. 2. Schematic view of the frontal networks.

frontotemporal dementia reportedly do better on tests of constructions and calculations (93). Performance in other realms may also be impaired because of a lack of motivation or mental activation. Memory is compromised mainly at the encoding or retrieval stages. With cueing, recognition memory is often relatively well preserved. There is diminished spontaneous verbal output that over time may progress to mutism. CT or MRI tend to show involutional changes in the frontal regions and functional imaging may show diminished perfusion in frontal lobes and anterior temporal regions (50,51). The Lund and Manchester research groups have proposed specific criteria for the diagnosis of frontotemporal dementia, based on behavioral, affective, and cognitive impairments and the results of investigations (50). Table 5 summarizes the diagnosis criteria. The frontotemporal dementias reportedly account for 10-20% of cases of degenerative dementias (87). A recent epidemiological study of the Dutch population suggested that 38% of patients with FTD had a strong family history of dementia (vs. 15% of controls) (93a). Approximately 43% of FTD patients with a family history of dementia were found to have a mutation in the tau gene located on chromosome 17 (93b). Intense interest has developed in investigating the relationship between non-Alzheimer's degenerative dementias and abnormalities linked to chromosome 17 (93 c).

On a pathological plane, this dementia syndrome is most often associated with marked atrophy of the frontal lobes and anterior temporal regions and histologically with neuronal loss and gliosis (30,88). Also, 20% of cases also have Pick bodies and ballooned cells, which are pathognomonic for Pick's disease (88). The preponderance of pathology in the frontal lobes and anterior temporal regions accounts for the profile of cognitive and personality changes. This pattern of dementia is rarely associated with the plaque and tangle pathology that defines Alzheimer's disease (88). Lewy body dementia (in which there is widespread distribution of Lewy bodies in brainstem, basal forebrain, and cortex) can present with prominent behavioral changes and has recently been re-

ported as a fairly common form of degenerative dementia with autopsy series suggesting that it may be seen in 15-25% of cases (94-96). Lewy body dementia has been associated with fluctuating cognitive impairment, transient episodes of marked confusion, a high incidence of visual and/or auditory hallucinations and delusions. It is most often accompanied by extrapyramidal signs or heightened sensitivity to a neuroleptic medication.

Dementias that exhibit prominent impairments in attention and executive functioning probably have the widest differential diagnosis and constitute many of the potentially reversible conditions. Table 6 provides a list of non-degenerative diseases with prominent changes in attention and behavior that includes the dementia of depression (also known as "pseudodementia"). It has

Table 6

Nondegenerative Disease With Prominent Changes in Attention and Behavior

Toxic-metabolic disease (e.g., hypothyroidism, or side effects from medications) Alcohol-related dementia

Space-occupying lesions (especially to the frontal lobe, such as subdural hematoma or tumor)

The dementia of depression (also known as "pseudodementia")

been estimated that the dementia of depression accounts for about 5% of dementias in general and about 25% of the potentially reversible causes of dementia (36). On mental state examination, there are often impairments in attention, concentration, processing speed, and spontaneous behavioral output. Motivation tends to be limited and the patient may complain of not knowing the answers, rather than offering incorrect responses. Difficulties with memory tend to be at the level of encoding and for some retrieval, with relatively preserved recognition memory after delay. There is no aphasia, although word retrieval may be slow. Somatic complaints are not uncommon. There may or may not be vegetative symptoms or past psychiatric history of depression. Clinicians should have a low threshold for treating depression, preferably with medications like the serotonin reuptake inhibitors (SSRIs) that have relatively low anticholinergic side-effects. Unfortunately, some patients who initially present with depression go on to exhibit a progressive dementia despite appropriate treatment for their mood disorder (97-99). In such cases, the depression was probably an early manifestation of their degenerative process. It has been shown that patients suffering from degenerative dementias are at increased risk for developing symptoms of depression that often manifest themselves early in the course of their illness (100-102).

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