What is dementia?

Dementia is not a specific disease as such, but rather a group of symptoms (known as a syndrome) which can result from a variety of diseases.¹ These symptoms include memory loss, cognitive decline and mood changes. The symptoms of dementia worsen over time and are more severe than those expected as a result of healthy biological ageing.¹ There are many different types of dementia, which are associated with distinct symptom profiles. This will later be addressed whilst discussing the differences between Lewy body dementia and frontotemporal dementia. According to the Alzheimer’s Society, approximately 982,000 people in the UK are currently living with dementia.² As people live longer now than in the past, and dementia is an age-related syndrome, this figure is predicted to increase by 43% (to 1.4 million) by 2040.

Differentiating between types of dementia

There are many different types of dementia, each of which presents itself with subtle differences in the collection of symptoms that patients display. This is, in part, due to the range of diseases which can cause dementia.³ As different areas of the brain are specialised in different functions, differences in the area damaged in early disease stages give rise to variations in early dementia symptoms.

Frontotemporal dementia

Frontotemporal dementia (FTD) refers to a collection of symptoms which arise as a result of damage or degeneration primarily to the frontal and temporal lobes.⁴ These brain areas play significant roles in impulse control, behaviour, executive function (i.e. problem-solving, planning and organisation skills) and speech and language processing and production. There are two subtypes of FTD, including behavioural variant frontotemporal dementia (bvFTD) and primary progressive aphasia (PPA).

Behavioural variant frontotemporal dementia

BvFTD is a type of dementia characterised by profound changes to an individual’s personality or behaviour. Symptoms of bvFTD include:^4,5

• A lack of empathy or emotion for others, including loved ones like friends and family
• Lack of impulse control: This could include behaviours such as making inappropriate comments or gestures and engaging in risky behaviours such as gambling or shoplifting
• Executive function deficits: Individuals with bvFTD often struggle with tasks such as arriving on time, planning activities, and remembering to take medications at specific times of the day
• General apathy: This might manifest as a lack of interest in activities which used to be important to the individual, such as spending time with family, taking part in hobbies, and even maintaining personal hygiene
• Changes in eating and drinking habits which are excessive or inappropriate

Primary progressive aphasia

On the other hand, PPA refers to dementia syndromes which are characterised by a distinct deficit in speech and language.⁶ This is usually due to a condition which causes damage or degeneration of the temporal lobes, which contain Wernicke’s area and important connections to Broca’s area, alongside important structures which process semantic knowledge, such as the medial temporal lobe (MTL). There are three types of PPA⁶ called progressive non-fluent aphasia, logopenic dementia and semantic dementia, which have subtle differences in symptoms:

Symptoms of progressive non-fluent aphasia (PNFA):

• An inability to use correct grammar in speech production, resulting in non-fluent speech (agrammatism)
• Difficulty understanding the meaning of a sentence
• Some behavioural deficits are present, but they are not as severe as those seen in bvFTD in the early stages
• Apraxia of speech: difficulty coordinating the muscles needed to produce correct word sounds during speech, resulting in abnormally effortful and distorted speech^7,8

Symptoms of logopenic aphasia:

• Deficits in single-word finding
• Distorted speech, e.g. slow and effortful speech with pauses. Speech slows as the underlying disease progresses
• Unlike PNFA, people with logopenic aphasia can speak with some fluency when making small talk or when using mostly common/high-frequency words. However, when a sentence calls for a more uncommon or unfamiliar word, speech becomes distorted and less fluent⁹

Symptoms of semantic dementia (SD):

• Inability to recognise objects (agnosia), name objects (anomia) and recognise familiar faces (prosopagnosia) that is not explained by other causes such as visual impairment
• Loss of semantic knowledge – the ability to understand the meaning of objects
• Inability to produce meaningful speech. Unlike PNFA, people with SD can produce sentences that are fluent and make grammatical sense, but are often vague and lack meaning
• Deficits in conceptual knowledge. This may present as an inability to group items into categories, e.g. correctly sort items into categories such as fruits vs vegetables^10,11

Motor symptoms in FTD

In all types of FTD, patients may experience motor symptoms, specifically as the disease which is causing the dementia progresses.⁴ This can include muscle weakness, gait disorder, muscle stiffness, difficulty swallowing and Parkinsonism (e.g. tremor, bradykinesia – slow movements, and rigidity).^9,10 There is also a strong link between FTD and motor neuron disease, where the same genetic mutation (C9ORF72) has been implicated.¹²

Lewy body dementia (LBD)

LBD refers to dementia syndromes caused by the accumulation of protein clumps in the brain called ‘Lewy bodies’.¹³ LBD is a progressive neurodegenerative disorder, meaning that both the damage in the brain and the symptoms this causes become more severe over time. The two main types of dementia syndromes that are caused by Lewy bodies are dementia with Lewy bodies (DLB) and Parkinson’s disease dementia (PDD). Additionally, studies have shown that the brain changes seen in Alzheimer’s disease – amyloid plaques and tau neurofibrillary tangles – are also often found in the brains of patients with LBD.¹⁴

Symptoms of LBD include:

• Detailed visual hallucinations
• Cognitive decline. This includes memory loss, impaired ability to pay attention to tasks, and impaired executive function (e.g. problem-solving, planning and organisation)
• Parkinsonism symptoms. E.g. tremor, bradykinesia, shuffling gait and rigidity
• Sleep disorders such as REM sleep behaviour disorder (RBD) – where patients act out their dreams - and excessive daytime sleeping. Degeneration of the brain's ‘body clock’ leads to a dysfunctional circadian rhythm, meaning that patients may remain active throughout the night and sleep more during the day^13,14

Importance of correct diagnosis and treatment

Different types of dementia have distinct causes, symptoms and patterns of progression over time. This means that accurate diagnosis of dementia type is essential to form specialised care plans to support patients and their carers in managing the most challenging symptoms that the patient faces. For example, someone with bvFTD may benefit most from therapies which address behavioural change and impulse control. In contrast, someone with PPA may benefit from speech and language therapies to aid their verbal communication abilities.

Similarities and differences between Lewy body dementia and frontotemporal dementia

Motor symptoms

Patients with LBD or FTD may experience motor symptoms as a result of the underlying neurodegenerative disease. Parkinsonism is a common symptom of LBD (sharing pathology with Parkinson’s disease) and is also seen in FTD, particularly in those who have the C9ORF72 mutation (also known as the motor neuron variant). However, motor symptoms tend to present earlier in LBD and in more advanced disease stages in FTD.

Cognitive impairment

Cognitive impairment is a common symptom of both LBD and FTD; however, the specific cognitive functions which are impaired vary between the two types of dementia, even within their own subtypes. For example, individuals with semantic dementia have deficits in recognising objects or familiar faces, with little or no behavioural deficits in the early stages. Whereas patients with bvFTD suffer from sudden behavioural changes but do not typically have issues in remembering object names or familiar faces. Although both fall under the FTD umbrella, they have vastly different cognitive symptoms.

Episodic memory

Episodic memory refers to one’s subjective memory of events. An example of a memory which would be considered ‘episodic’ in nature would be the recollection of a previous birthday. In LBD, a characteristic symptom is a loss of episodic memory, where memory for facts, object names, and concepts is initially preserved. On the other hand, people with FTD do not tend to face episodic memory loss, but instead are more likely to have deficits in behaviour (bvFTD), semantic memory – a loss of memory for knowledge, categories and concepts (SD) or speech and language production (PNFA).

Mood changes 

Unfortunately, many types of dementia can give rise to mood disorders, FTD, and LBD included. It is not uncommon for the early stages of dementia to be misdiagnosed as dementia, anxiety or bipolar disorder, as such mood disorders can also cause apathy, confusion and forgetfulness.¹⁷ Not only do the neurological causes of dementia give rise to changes in mood, but the diagnosis of dementia, and the uncertainty that comes with it, can cause a lot of distress for a patient and their loved ones.^15,16

Summary

FTD and LBD are classified as types of dementia. Although they share general symptoms such as cognitive impairment, memory loss and mood changes, both conditions also present unique symptoms. FTD presents with symptoms that affect impulse control, behaviour and executive function. In contrast, LBD has symptoms that affect movement and sleep, as well as present with hallucinations. Accurate diagnosis is crucial because these conditions present uniquely, and ensures individuals receive the correct specialised care and treatment to manage their symptoms.