Frontotemporal Lobar Degeneration: An Overview

Professor David Neary, Consultant Neurologist

Functions of the Brain

To get a good understanding of fronto-temporal dementia and semantic dementia, it is useful to look at the brain and the way it functions (see diagram).

The different areas of the brain play different roles. The posterior areas (i.e. the parietal and occipital lobes) are responsible for our visual functions. They help us to see what things are and where they are in space. The temporal lobes play an important role in memory and language. They enable us to learn and store new information. Finally, the frontal lobes are responsible for organisation and control of information. They enable us to generate plans and make decisions. This is often referred to as ‘executive function’

Dementia: Alzheimer's disease Vs Frontotemporal lobar degeneration

Traditionally, ‘dementia’ has been viewed as a singular, global decline of mental functions.  However it is increasingly clear that this is not the case.  Different disease processes affect specific parts of the brain, resulting in diverse patterns of mental decline.  The location of the disease determines the symptoms that occur. 

As you can see on the diagram, fronto-temporal dementia and semantic dementia affect areas towards the front of the brain, whereas Alzheimer’s disease affects the areas at the back.  The different disease processes are therefore associated with different symptoms.  

Patients with Alzheimer’s disease typically have problems in memory, visual and spatial function, and language.  They find it difficult to learn new information, see things around them, and retrieve words in conversation.  In contrast to their often debilitating mental decline, they are fully insightful and concerned about their problems, with preserved personality and behaviour. 

Patients with fronto-temporal dementia and semantic dementia are entirely different.  Since the posterior areas of the brain remain unaffected, there are no problems in visual function.  However, the affected frontal areas are responsible for controlling behaviour, meaning that there are often profound changes in personality. 

Fronto-temporal lobar degeneration

Fronto-temporal dementia and semantic dementia form part of the same disease, known as ‘fronto-temporal lobar degeneration’.  The underlying disease process is the same.  It is the location of the disease that determines the symptoms and the corresponding name that is given to the dementia.  As you can see in the earlier picture, in fronto-temporal dementia, the disease primarily affects the frontal lobes, whereas in semantic dementia the disease selectively affects the temporal lobes.  The two disorders will be described separately to illustrate the differences between the symptoms.

Fronto-temporal dementia

Fronto-temporal dementia (FTD) typically affects people below the age of 65.  About half of the patients that we see report a family history of similar problems, and in a small proportion of these cases, there is a specific genetic fault associated with developing the disease.  However, FTD also occurs in people who have no other affected family members. 

Patients are typically physically fit.  Initial changes are apparent in mental function only.  As the disease progresses, reduced activity and physical slowing may occur.

Symptoms arise gradually, making it difficult to pinpoint the very beginning of the disease.  Carers often report with hindsight that their relative showed signs of depression, anxiety, over-sentimentality, or hyperchondriasis even before they noticed clear changes in behaviour.  Commonly, referral to doctors occurs following difficulties at work, or social problems within the family.  

FTD principally affects personality and behaviour.  Below are some of the behavioural changes that can occur: 

  • Irritability
  • Egocentricity/selfishness
  • Inappropriate/disinhibited behaviour
  • Lack of embarrassment
  • Loss of feeling for others
  • Poor insight into problems
  • Loss of interest in former hobbies
  • Apathy and need for prompting
  • Restlessness/wandering behaviour
  • Mental rigidity/inflexibility
  • Obsessive/ritualistic traits
  • Odd mannerisms
  • Preoccupations
  • Poor personal hygiene
  • Changes in eating behaviour

Symptoms are not exactly the same for all sufferers, and depend on which part of the brain is most affected.  Generally speaking, there appear to be two different patterns: 

Apathetic: Patients are inert and inactive, and act as if they are depressed.  However, they do not complain of feelings of depression, and remain unconcerned about their lack of motivation and drive. 

Disinhibited: Patients are overactive and act inappropriately in social situations.  They show a lack of concern for the feelings of others and are often restless and irritable. 

In addition to changes in personality, people with FTD may also have problems in memory, language, and ability to perform daily activities. 

Sufferers often have problems in concentration, which in turn can affect memory ability.  If you don’t pay attention to what someone is telling you, it will be difficult to remember it afterwards.  This appears to be the reason why FTD patients remember some things and not others – it is not that they ‘forget’ information, rather, that they fail to take it in when it is presented.   

Spontaneous speech may reduce gradually, and eventually, sufferers may become totally silent.  Patients may also develop ‘verbal stereotypies’, repeating the same phrase or topic over and over again.  Sometimes patients may use the wrong words when talking – this is related to the temporal lobes, and will be discussed further in the ‘semantic dementia’ section. 

Performing everyday activities
Patients may have problems in sequencing and ordering task components, generating appropriate strategies, and grasping instructions.  In everyday life, this may be reflected by reduced ability to perform seemingly simple tasks, such as putting clothes on in the right order, or using household gadgets.  This is related to the failure of the frontal lobes in controlling and organising information. 

Semantic Dementia

Semantic dementia (SD) is another clinical manifestation of frontotemporal lobar degeneration, associated with shrinkage of the temporal lobes (see diagram). SD is a relatively rare disorder and is much less common than FTD. However, like FTD, people with SD tend to be affected at a relatively young age, generally between the ages of 50 and 65. Relatives report a history of a similar disorder in the family in about a quarter of cases.

In SD, people progressively lose their ability to remember the meaning of words, objects and faces. Changes may also occur in people’s behaviour, although these are qualitatively different from those observed in FTD.

Physical signs
Sufferers are generally fit and physically healthy although they may become slowed down in the later stages of the disease.

Problems in language tend to occur first. People with SD have difficulty naming and often use the incorrect word in conversation (e.g. calling a lion a “dog” or saying “water” for milk). They have difficulty understanding the meaning of words and may fail to recognise relatively simple words in conversation. Sufferers may also repeat the same expression (verbal stereotypy) over and over again (e.g. “oops a daisy”, “Well, it’s one of those things”). Nevertheless, their speech is generally fluent and effortless, which may initially give relatives the impression that they do not have any primary difficulty with language. Moreover, their repetition is good, and they can generally read and write words they do not understand.

Visual recognition
The disorder may also affect the ability to recognise objects and faces. The sufferer sees normally (and so can distinguish when two objects or faces are the same or different), but is no longer able to attribute any meaning to what they see. This is why sufferers may still be able to draw accurately objects that they no longer recognise. Occasionally, difficulties in visual recognition may occur before language problems.

Sufferers do have problems with memory, but it is with a specific type of memory called “semantic memory”. There are two different types of memory which are processed in different areas of the brain: “personal memory”, which corresponds to memory for day-to-day events, such as remembering what you ate for dinner yesterday or where you went on your last holiday; and “semantic memory”, which relates to your general knowledge about the world and, more specifically, to what words and objects mean and represent. In SD, people’s personal memory is well preserved, so they have no difficulty keeping appointments or remembering what they have done in the past few weeks. However, they do have a problem with their semantic memory, which means they cannot remember the significance of words, objects and faces.

Semantic memory does not break down in an all-or-none fashion and people with SD typically retain partial knowledge of objects and words. Interestingly, sufferers tend to retain information about things that are personally relevant to them in their everyday lives. For example, they may be able to recognise their own kettle but are unable to make a cup of tea with someone else’s kettle because they do not understand its function anymore. Similarly, they will be better able to recognise names and faces of people they see regularly (e.g. spouse, visiting health worker) than of people they only see occasionally (e.g. relatives at a family function). This “autobiographical” effect even extends to words and place names: people are more likely to understand names of countries and cities they have visited recently (e.g. on holiday) than places they have little personal experience of.

Individual differences
Although the disorder affects several domains, such as words, objects and faces, people do vary in the extent to which these domains are affected. Some sufferers have particular difficulties in word meaning and only develop problems in recognising faces later on in the course of the illness. For other people, the main problem lies in the visual domain, and they may be unable to recognise people’s faces at a time when they can still understand their names. These individual differences between word meaning and visual recognition reflect the location of shrinkage in the brain. Although both temporal lobes of the brain are affected in SD, one side may become more heavily affected than the other. Shrinkage of the left temporal lobe is associated with better recognition of faces / objects and relatively poor understanding of word meaning, whereas predominant shrinkage of the right temporal lobe is associated with poor face recognition and better understanding of words.

Difficulty in comprehension is by far the most important feature of SD, however, sufferers do also show changes in their behaviour. These changes are generally more subtle than those observed in FTD, and have a more obsessional quality. Sufferers tend to focus on a restricted range of activities (e.g. house work, sewing, walking), which they pursue obsessively. They develop a preference for fixed routines and often become preoccupied by time, so that certain activities are always carried out on set days and at fixed times. Certain people also become excessively parsimonious and may hoard their money in different places around the house. Sufferers generally become more self-centred although they rarely show the marked loss of empathy and lack of self-care typical of FTD.