Assessment of cognitive impairment

The cognitive symptoms, which appear early in FTD, may be difficult to evaluate due to the patient's emotional and behavioural changes. Distractibility and slightly reduced recent memory are common findings and remote memory is also impaired although to a lesser extent than in Alzheimer's didease. The patients show significant impairment on 'frontal-lobe' tests such as the Wisconsin card sorting test, word fluency test, and the Stroop and trail-making tests. The early test profile is characterized by slow verbal production and relatively intact visuospatial ability, reasoning, and memory, while intellectual and motor speed are reduced. (39» Early Alzheimer's disease usually shows a relatively preserved verbal ability and simultaneous impairment of reasoning ability, verbal and spatial memory dysfunction, dysphasia, and dyspraxia/39,40» Difficulties in understanding instructions are found early only in a minority of FTD cases. Misspelling and dyscalculia are sometimes reported early in FTD.

Discrimination between FTD and Alzheimer's disease can be based on a short test-battery (verbal ability, visuospatial ability, and verbal memory), when used in the context of a neuropsychological evaluation of qualitative as well as quantitative aspects of test performance. (3 d1» Using a screening instrument based on frontal release signs, awareness of social/ethical dilemma in a short story, and the number of preservation errors, FTD was classified correctly in 83 per cent, validated against clinical diagnosis.(42» The Mini-Mental State Examination(43» does not reflect the FTD patient's true competence because of influence of motivational and behavioural factors.(44»

The deterioration of personality and behaviour in FTD contrasts with the comparatively spared spatial orientation, receptive speech, and practical ability. Differential diagnosis

Differential diagnosis between FTD and Alzheimer's disease and other dementias is often possible using well-defined clinical criteria, neuropsychological testing, and brain imaging. Organic dementias with frontal features are listed in T§b.l§...3..

Table 3 Organic dementia with frontal features

The clinical differences between FTD and Alzheimer's disease are often obvious at an early stage ( Table4). The initial stages of FTD are dominated by emotional and personality changes, and consequently severe dyspraxia, memory failure, and spatial disorientation develop comparatively late with the relative sparing of the temporoparietal occipital cortical areas. In contrast, early-onset Alzheimer's disease is characterized by memory failure, dyspraxia, dysgnosia, and impaired sense of locality, whereas habitual personality traits, social competence, and insight are better preserved in agreement with the consistent pattern of cortical involvement. A minority of Alzheimer's cases, about 5 per cent, show a marked frontal-lobe involvement at an early stage and consequently also present a frontal-lobe clinical pattern in addition to the temporoparietal symptoms/38' The PEMA syndrome with stereotypy of speech (palilalia), echolalia, late mutism, and amimia is typical of FTD and rare in Alzheimer's disease. Certain neurological features may also contribute to the differentiation between the two, for example generalized epileptic seizures, myoclonus, and logoclonia are more prevalent in Alzheimer's disease. Moreover, EEG may remain normal in FTD cases with evident signs of dementia while EEG in Alzheimer's disease is almost always pathological. The Kluver-Bucy syndrome in Alzheimer's disease is usually less complete than in FTD with less hypersexuality and utilization behaviour, supporting the suggestion that frontal as well as temporal lobe involvement is needed to produce the syndrome in humans. Imitating behaviour, seen as echolalia and repetition of other people's gestures, is more prevalent in FTD than in Alzheimer's disease.

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Table 4 Clinical characteristics in frontotemporal dementia (FTD) and Alzheimer's disease (AD)

Vascular dementia with frontal emphasis may be caused by selective incomplete white-matter infarction, Binswanger's disease, and frontal and strategic thalamic infarctions. The frontal-lobe dysfunction caused by vascular lesions may closely mimic the course of FTD, when developing gradually without dramatic onset on fluctuations. (3,45)

The clinical distinction between FTD and Huntington's disease may be difficult when personality changes and psychotic features dominate, and when the neurological characteristics of Huntington's disease are less obvious or appear late in the course. Brain imaging showing striatal involvement and genetic analysis may contribute to the diagnosis.

Progressive supranuclear palsy and the rare progressive subcortical gliosis may also show a frontal-lobe clinical and imaging pathology. (464Z) Corticobasal degeneration may also present with a dementia of frontal-lobe type in addition to the typical asymmetric akinetic-rigid dystonic syndrome. These three diseases have grown increasingly important because of studies suggesting a linkage to chromosome 17. (!2>

Dementia of the frontal and frontal subcortical type is also found in Creutzfeldt-Jakob disease, (38) in the AIDS dementia complex, and in general paresis. Classification

The Lund-Manchester consensus (Table.,.?) is recommended as guidelines for clinical recognition of FTD. Guidelines for diagnosis of dementia, such as the NINCDS-ADRDA criteria for diagnosis of Alzheimer's disease, (48> may easily lead to the inclusion of FTD and Pick cases in the Alzheimer's group. DSM-IV presents Pick's disease as 'One of the pathologically distinct etiologies among the heterogeneous group of dementing processes that are associated with frontotemporal brain atrophy. The specific diagnosis of a frontal-lobe dementia such as Pick's disease is usually established at autopsy with a pathological finding of characteristic intraneuronal argentophilic Pick inclusion bodies'. Moreover, the frontal-lobe dementias are 'characterized clinically by changes in personality early in course, deterioration of social skills, emotional blunting, behavioural inhibition, and prominent language abnormalities. Difficulties with memory, apraxia and other features of dementia usually follow later in the course.' (!>

ICD-10(49> describes 'Dementia in Pick's disease' as 'a progressive dementia, commencing in middle life (usually between 50 to 60 years) characterized by slowly progressive changes of character and social deterioration, followed by impairment of intellect memory and language functions with apathy, euphoria and (occasionally) extrapyramidal phenomena. The social and behavioural manifestations often precede frank memory impairment.' ICD-10 points out that Pick's disease is a non-Alzheimer degenerative brain disease, but it does not introduce the concepts of frontal-lobe dementia or FTD.

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