Dementia: Types and Differentials

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This article provides an overview of the different types of dementia and other causes of dementia-like symptoms. We’ll end with a simplified table of parts of the brain and their functions.


Introduction

  • Dementia – it’s not a normal part of old age. It’s not just a lapse in memory.
  • Dementia is irreversible, progressive decline and impairment of more than one aspect of higher brain function (concentration, memory, language, personality, emotion). This occurs without impairment of consciousness.
  • Dementia can only be proven post-mortem with histological evidence. However, diagnosis is often made based on the gathering of clinical information – from the history (patient and collateral), cognitive tests (6-CIT, GPCOG, 7-minute screen etc), and formal neuropsychological assessment.
  • Other differential diagnoses need to be excluded (delirium etc) so often baseline blood tests and a CT head are performed during a dementia assessment.

Alzheimer’s Dementia

Epidemiology

  • Slightly more common in females.
  • The most common cause of dementia in the UK accounting for about half of all dementia diagnoses.

Pathophysiology

  • Amyloid plaques: clumps of beta-amyloid and degenerating bits of neurons and other cells which lurk in between nerve cells.
  • Neurofibrillary tangles: bundles of twisty filaments within neurons, mostly made from tau protein.
  • The accumulation of these leads reduction in transmission of information, and eventually to the death of brain cells, with abnormal depositions remaining post-mortem.

Symptoms

  • Usually begin after the age of 60 (though there are “early-onset” cases, most of which involve genetics).
  • Can affect all areas of the brain: many functions and abilities can be impacted upon and eventually lost.
  • The most common presenting symptom is memory loss, with evidence of varying changes in planning, reasoning, speech and orientation.

General Progression

  • Alzheimer’s dementia tends to progress steadily over time.

Vascular Dementia

Epidemiology

  • More common in males, generally thought to be due to their increased risk of vascular disease.
  • The second most common type of dementia.
  • Increased prevalence in those who have had a stroke (9x higher than the general population).

Pathophysiology

  • There are several subtypes of vascular dementia, the most common of which are multiple (commonly small) cerebrovascular infarcts.
  • The most commonly affected areas of the brain are the white matter of both cerebral hemispheres, grey nuclei, thalamus and the striatum.
  • Hypertension is a major risk factor for diffuse vascular dementia.
  • Other general “vascular” risk factors increase the chances of developing vascular dementia and can increase cognitive decline – smoking, diabetes mellitus, hyperlipidaemia, obesity, hypercholesterolaemia etc.

Symptoms

  • Single infarct vascular disease: classically cognitive impairment (acutely or subacutely) following the event.
  • Functional deficits are often seen before memory impairment.
  • Mood disturbances and mood disorders are common in vascular dementia.
  • Psychosis, delusions, hallucinations and paranoia can often be seen, especially in later stages.
  • Patients should be screened for depression and for signs of psychomotor retardation (often a more common feature than positive signs of depression).
  • Emotional lability can be prominent.

General progression

  • ‘Stepwise’ – often shows a period of stability at one level of functioning, before an acute decline progression, followed by another period of stability.
  • There is little way to predict how quickly (or when) these declines will occur.

Lewy-Body Dementia

Epidemiology

  • Appears to affect slightly more men than women. 
  • Mostly affects those over the age of 50.

Pathophysiology

  • Spherical “Lewy Body” proteins are deposited in the brain (alpha-synuclein for those who love the science words).
  • These Lewy Bodies are also present in Parkinson’s disease – the difference being that in Parkinson’s they are mainly deposited in the substantia nigra, whereas they are more widespread in Lewy-Body dementia.

Symptoms

  • Often involves visual hallucinations and Parkinson-like symptoms.
  • If physical symptoms precede cognitive decline by more than a year, the diagnosis is often Parkinson’s, with superimposed cognitive decline.
  • Fluctuation in cognitive ability is common.
  • At presentation, problems multitasking and performing complex cognitive actions are more likely to the primary issue (rather than memory).
  • Sleep disorders are a common manifestation.

General progression

  • Fairly rapidly progressive, with death most commonly in the first 7 years post-diagnosis.

Mixed

  • Mixed dementia is exactly what it says on the tin.
  • This is diagnosed when patients have evidence of more than one type of dementia (often Alzheimer’s and vascular dementia) based upon clinical or neuroimaging evidence.

Frontotemporal Dementia (including Pick’s disease)

Epidemiology

  • Much less common type, but responsible for a significant number of diagnoses of dementia in under 65s.
  • Tends to affect both sexes equally.
  • There are several types of frontotemporal dementia, one of which is Pick’s disease, but often all frontotemporal dementias are mislabelled Pick’s.

Pathophysiology

  • Neuron damage and death in the frontal and temporal lobes.  
  • The atrophy is due to deposition of abnormal proteins (often tau protein) within the lobes.
  • There is thought to be a genetic component in about a quarter of cases.

Symptoms

  • Tend to present with one of three clinical pictures (or an overlap): changes in personality and behaviour (which may be labelled psychiatric), or as progressive language difficulty and aphasia.

Behavioural presentation

  • Altered emotional responsiveness, apathy, disinhibition, impulsivity.
  • Progressive decline noted in interpersonal skills.
  • Changes in food preference, more childlike amusements.
  • Obsessions and rituals may also be noted.

Semantic presentation

  • Progressive decline in the understanding of word meanings.
  • Speech may still be fluent, but there is difficulty in name-retrieval and use of less precise terms.
  • Are unable to determine the meanings of common words when asked.
  • This tends to develop into the inability to recognise objects, or familiar faces (prosopagnosia).

Non-fluent presentation

  • Progressive breakdown in the output of language.
  • The speech takes effort and is not fluent.
  • Generally display speech apraxia (poor articulation) or disorders of speech sound.
  • There also tends to be impaired comprehension of sentences and an impact on literacy skills.
  • Over time, all three initial presentations tend to emerge and worsen.
  • There is also evidence for the development of motor disorders either before or alongside these symptoms.

General progression

  • There is great variation in progression, but average life expectancy is 8 years post-diagnosis.

Quick Notes on Some Differentials!

Prion Protein Diseases (focussing on  Creutzfeldt-Jakob Disease)

  • Infectious prion proteins cause diseases such as Creutzfeldt-Jakob disease (CJD).
  • This can be sporadic or ‘variant’.
  • Sporadic CJD tends to affect those over the age of 40 and is a one in a million occurrence.
  • Variant CJD is caused by eating meat infected by bovine spongiform encephalopathy through eating infected cattle meat.
  • The disease can be indolent for many years.
  • To begin with, it may present as minor memory lapses, mood disturbance and loss of interest.
  • This quickly (over weeks) becomes more prominent and is followed by unsteadiness and physical clumsiness.
  • Progression then involves stiffness, jerking movements, incontinence and aphasia.
  • Death usually occurs within 6 months of symptom presentation.

HIV-related Cognitive Impairment/Dementia

  • Almost half of all people with HIV experience some symptoms relating to their brain, which can include mild cognitive impairment and dementias.
  • With the use of antiretrovirals around 2% will still go on to develop dementia.
  • Milder cognitive impairment can be caused indirectly (by a weakened immune system leaving the brain more vulnerable) or directly by the virus.
  • Symptoms can include short-term memory problems, issues with concentration, thinking and language skills.
  • Mood disturbance is very common and makes the diagnosis more difficult to differentiate from depressive episodes.

Normal Pressure Hydrocephalus

Pathophysiology

  • Abnormal build-up of cerebrospinal fluid in the ventricles causes pressure to increase in the brain tissue, producing symptoms of cognitive impairment.
  • Can occur at any age, but more common in the elderly.
  • Other factors which increase the likelihood of development include head trauma, infection or inflammation in the brain, tumour and subarachnoid haemorrhage.

Symptoms

  • Progressively worsening memory lapses
  • Personality and mood disturbances
  • Difficulties with walking
  • Dementia
  • Urinary incontinence

Management

  • To treat normal pressure hydrocephalus, a shunt is surgically placed to drain excess CSF into the abdomen, relieving pressure on the brain. 
  • The success of treatment depends on prompt diagnosis and treatment; some may make an almost complete recovery.

Severe Depression

  • Severe depression can involve cognitive impairment and can masquerade as the early stages of dementia.

“Mild Cognitive Impairment”

  • This term is used for people with memory problems or higher cortical thinking, not severe enough to interfere with everyday life.
  • Mild cognitive impairment can be caused by a range of circumstances and conditions.
  • Each year, 10-15% will go on to develop a form of clinical dementia.
  • Other causes of cognitive impairment can include stroke, depression, stress, physical illness and drug side-effects – due to this, many with mild impairment may never go on to develop dementia, and some may even completely recover.

Brief Overview of Brain Functions

Area of the brain Function
Frontal lobe
  • Problem-solving, emotions, reasoning, planning, personality.
  • A site of many inhibitory functions.
  • Primary motor cortex: generates voluntary movements of muscles.
  • Broca’s area: (usually left) postero-inferior part of the frontal cortex, involved with motor aspects of speaking.
Temporal lobe
  • Perception/recognition of auditory stimuli, memory, speech.
  • Contains Wernicke’s area – helps with formulation/understanding of speech.
Parietal lobe
  • Recognition, movement, orientation, perception.
  • Primary sensory cortex: processes sensory stimuli.
Occipital lobe
  • Visual processing
Cerebellum
  • Posture, balance and coordination of movement

References

  1. Alzheimers.org website. Available from: [LINK]
  2. Dementia: assessment, management and support for people living with dementia and their carers. NICE Clinical Guideline 42. Available from: [LINK]
  3. National Institute on Aging. Advice for People Living with Lewy Body Dementia. Available from: [LINK]
  4. Patient.info. Dementia. Available from: [LINK]
  5. Medscape. Vascular Dementia. Available from: [LINK]

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