What is frontotemporal dementia? - Chapter 20

What different types of frontotemporal dementia are known?

After Alzheimer's and dementia with Lewy bodies, frontotemporal dementia (FTD) is the most common type of cortical dementia. This chapter focuses on three subtypes of FTD: the behavioural variant (BV-FTD) and two language variants, namely semantic dementia (SD) and progressive non-fluent aphasia (PNFA).

What is the clinical picture of frontotemporal dementia?

'Behavioural variant frontotemporal dementia' (BV-FTD) is characterized by prominent changes in personality and social behaviour, specific cognitive impairments, and language impairment. The most important behavioral changes in patients with BV-FTD are the decreased emotional involvement, emotional blunting, lack of initiative, apathy, and impaired judgement, as well as hyperactivity and restlessness. Patients are often more easily distracted, and there may be social disinhibition and a loss of decorum. In addition, impairments occur in social cognition. Often there is personal neglect, and patients frequently act irresponsibly because they are unable to determine the consequences of their behaviour. Although there are no (or subtle) language problems in the initial phase, after a while the patient will switch to 'economy of speech': they no longer start a conversation themselves and only answer questions. Finally, the patient will become mute. Within BV-FTD there are three subtypes (Snowden, Neary, Mann & Benson, 1996):

1. A profile with disinhibition, distractibility, and hyperactivity.

2. A profile with apathy, lack of initiative, and behavioural withdrawal.

3. A profile with stereotypy and compulsive behaviour. 

Sub-types of frontotemporal dementia

Only in a few cases does the BV-FTD patient develop motor neuron disease (MND); a selective motor disorder that is initially characterized by dysarthria (difficulty with articulation), muscle atrophy and minor muscle twitches, but later also causes loss of strength in the arms and legs. Such a patient then suffers from FTD-MND. Progressive non-fluent aphasia (PNFA) is an isolated gradually progressive deterioration in language production (language comprehension is relatively unaffected). In the initial phase there is good insight into illness, attempts at self-improvement and cognitive functioning are also intact. There are, however, many feelings of frustration and depression. In the later phase more behavioral changes are noticeable such as egocentrism, apathy and a lack of self-care and motivation. The insight into illness diminishes and stereotypical behavior increases. Semantic dementia (SD) is a progressive disorder characterized by a multimodal breakdown of semantic knowledge. The spontaneous language is fluent, but comprehension of the meaning of words is greatly impaired. As a result, spoken language becomes increasingly empty as the disease progresses. It starts with word-finding problems and conceptual loss of comprehension of words and objects. Subsequently the problems expand from the verbal modality to the non-verbal modality. Behavioral changes are related to compulsive behaviour and stereotypy. Although the behavioral changes resemble the behavioral variant of FTD, these are more compulsive in SD.

Diagnostic criteria for frontotemporal dementia

For the diagnosis of BV-FTD there must be a deterioration of social behavior including emotional blunting and loss of insight early in the course of the illness. In addition, there should be impairment in the regulation of personal behaviour at an early stage. Other disorders (such as stereotypy and language disorders) are only supportive, but not essential for a diagnosis. In the case of PNFA, there must be agrammatism, word-finding problems, and phonemic paraphasias. SD involves prominent verbal or visual semantic impairments. In addition, visuoperceptual impairments are often involved (such as object agnosia).

What does frontotemporal dementia look like?

The onset of FTD is usually before the age of 65 years. The average duration of the disease is eight years. The duration of the disease is shortest in patients with FTD-MND with an average value of three years. There appears to be no influence of gender on prevalence. The three genes related to the pathogenesis of FTD are the MAPT gene, the GRN gene and the C90RF72 gene. Someone with a mutation to one of the first two genes will almost certainly develop FTD. The last gene is related to familial FTD-MND. In addition to a gene defect, there is little to say about a possible cause. The three proteins that may be involved are tau, TDP-43 and FUS. A SPECT or PET scan is often made in the initial phase. At a later stage, an MRI scan mainly shows frontal and / or temporal atrophy and (asymmetrical) atrophy in the hippocampus in patients with the behavioral variant. In a PNFA patient, there is an asymmetrical atrophy especially on the left frontotemporal. In SD there is often bilateral or asymmetric atrophy of the temporal lobes (the left hemisphere is often worse affected) and hippocampal atrophy. There is no treatment for FTD yet.

Which cognitive impairments occur?

BV-FTD

A patient with BV-FTD is likely to have disturbances in attention (concentration), executive functions, abstract thinking, and language. Social skills are also often affected. Due to the behavioral problems patients are extremely easy to distract and often make only minimal effort ('economy of effort'). Therefore, the results of the neuropsychological assessment often need to be assessed qualitatively. The capacity of memory and orientation in daily life remains undisturbed for a long time, although subtle deviations do appear during tests (possibly due to a lack of motivation). Visual-spatial and constructive skills are also intact.

Progressive non-fluent aphasia (PNFA)

PNFA is a clear disorder in the use of language and in particular phonology and / or syntax. This is expressed in phonematic paraphasias and agrammatism. There are self-improvements (conduite d'approche). Reading and writing are also often disturbed. Word and object comprehension are relatively unaffected, just like the other cognitive functions.

Semantic dementia

Spontaneous language is fluent but the semantic understanding is strongly disturbed. Semantic paraphasias and generalizations are therefore often applied to cope with the significant word-finding and naming problems. The problem expands over time to the non-verbal modality. Subsequently, there are often visual-perceptual disorders. Repetition of words and sentences remains intact. Disorders in memory are limited to the semantic memory. Furthermore, there are no clear cognitive disorders until the final phase of the disease where executive functions become problematic.