Semantic Dementia

Information for patients and carers

What is Semantic Dementia?

Semantic dementia (SD) is a progressive loss of the ability to remember the meaning of words, faces and objects, which results from shrinkage of the temporal lobes of the brain.

Why haven’t I heard of semantic dementia before?

SD is much less common than other causes of dementia, such as Alzheimer’s disease, which is better known. In the past the general belief was that all people with dementia had the same disease, usually thought to be Alzheimer’s disease. It has only relatively recently that distinct disorders like semantic dementia have been recognised.  Another problem is that people use different names to refer to the same condition, which can make finding information confusing. Semantic dementia is known to be related to frontotemporal dementia. Other names commonly used for SD are “semantic variant frontotemporal dementia” or semantic variant Primary Progressive Aphasia. 

What are the symptoms?


The initial problems are often with words. People with SD may have difficulty remembering the names for things and may use words incorrectly (e.g. saying “water” for ‘milk’; “dog” for ‘lion’). Their loved ones often comment that their speech seems vague and they don’t use nouns often. People with SD don’t usually have difficulty in producing speech sounds, so their speech may sound entirely normal until you really listen to the words being used.

People may also have difficulty understanding what is said, and may ask for the meanings of words they would normally know.

Recognition of faces and objects

It’s common for people with SD to have difficulty recognising people whom they don’t see regularly.  They may also have difficulty in recognising things for what they are, for example, vegetables in the supermarket. It may be difficult for them to understand how to interact with objects.


People with SD do have a problem with memory, particularly with a certain type of memory: memory for what words mean, who faces represent, what objects signify.  This special type of memory is called ‘semantic memory’.  Memory in the sense of remembering to do things at the right time, remembering events, and the way to the shops is often not affected.

Personality and behaviour

People with SD may experience changes to their behaviour so that they seem inflexible, self-centred or less concerned for the feelings of others. They may be preoccupied with a few activities, have a fixed daily routine or like to do things at the same time each day.

Can the person with SD alter his/her behaviour?

No.  Changes in behaviour are a direct result of damage to brain cells and are not under the person’s conscious control.  Apparent selfishness or awkwardness is not the result of deliberate wilfulness.

Is the person with SD aware of what is happening to him/her?

People may have some awareness of difficulties leading to frustration and irritability.  However, individuals often do not appreciate the extent of changes in the same way as those around them do.  This can make it particularly difficult for loved ones, friends and formal carers.

Are there any physical changes?

People with SD typically remain physically well.  They may ‘slow up’ as the disease progresses. Weakness due to wasting of the muscles can occur, although this is very rare.

Will the symptoms become worse?

The disease is progressive, so symptoms do get worse over time. However, there is wide variation in the speed of progression.  Some people show little decline over the course of a year whereas others change more quickly.  Usually, monitoring a person’s progress over about a year will give a good guide as to the likely future rate of progression. Unfortunately there are no medicines to cure or treat the condition.

Are there ways to help?

Encouraging activities in which the individual can be successful can help to boost confidence and maintain independence.

Understanding is helped by doing.  Vocabulary relating to the sufferer’s daily life will be more meaningful than other vocabulary; objects that the patient uses will be recognised better than those which are not used; activities which they are involved in will continue to be meaningful for longer than those in which the person has no participation.  Encouraging and maintaining a variety of life experience will help to slow symptom progression.

The person with SD’s difficulty is in understanding meaning.  It can help understanding if words are put into context: speaking in complete sentences is better than communicating in short phrases or by single words.

At what age are people affected?

The condition most commonly affects people between 50 and 75 years. It is less common in the very elderly.  This is one factor that distinguishes semantic dementia from Alzheimer’s disease, which becomes more common as age increases. 

What is the cause? 

The disorder is a degenerative condition of the brain and is a type of frontotemporal lobar degeneration. These are a family of brain disorders affecting the frontal and temporal lobes of the brain. There are a few different causes of these changes in the brain but for most people with SD it is associated with the build-up of a protein called TDP-43. We know that this condition is not caused by external environmental or lifestyle factors, such as diet, occupational exposure or head injury. It can affect people from all walks of life and does not result from ‘over-use’ or ‘under-use’ of the brain.

Is semantic dementia inherited?

In most cases  semantic dementia is sporadic, which means it occurs ‘out of the blue’, with no history of similar problems in other family members. In a very small number of cases the condition appears to run in the family. Generally the risk of semantic dementis being inherited is very low unless other family members have the same condition. If you or your family have any particular concerns or questions please let us know.

Is there any treatment?

There is currently no treatment for the underlying disease. There are some drugs available, designed for use in other conditions such as anxiety and depression, which may alleviate symptoms of the disease. Any treatment options will be discussed with you by your doctor.

Is there research into the condition?

Yes, certainly. The aim is to understand the mechanisms that underlie this disorder, so that better treatments can be developed. Our department is an active contributor to research in semantic dementia and other degenerative disorders. If you would like to find out more about the research carried out in our unit, please visit our website or ask when you attend the clinic.