Dementia

Disease class: Brain diseases 

Disease class: Neurocognitive disorders

 Definition

An acquired and irreversible deterioration in intellectual function.

Around 10 per cent of people aged over 65 and 20 per cent of those aged 75 or over are affected to some extent. The disorder is due to progressive brain disease. It appears gradually as a disturbance in problem-solving and agility of thought which may be considered to be due to tiredness, boredom or depression.

As memory failure develops, the affected person becomes bewildered, anxious and emotional when dealing with new surroundings and complex conversations.

 Source: Black's Medical Dictionary (42nd ed, 2010, ISBN 978-1-4081-0419-4) 

 

Pathophysiology

There is an accelerated rate of neuronal death, and so the amount of matter in the brain decreases significantly. In autopsies, the brain is clearly smaller and lighter.

Sketched illustration of serial CT scans.View: coronal. Left: patient with dementia. Center: same patient after 5 months. Right: patient with advanced dementia

On brain scans, the ventricles (fluid-filled spaces in the brain which act like a waste-removal system) appear larger because there is less brain matter around them. The gyri (folds of brain tissue) appear smaller. The sulci (valleys of empty space between gyri) appear wider. There is more empty space between the brain and the skull.

 

Symptoms

• Short-term memory impairment, forgetfulness 
• Cognitive impairment 
• Declining attention
• Depression 
• Sleep disturbances, insomnia
• Passivity, social withdrawal
• Emotional instability 
• Loss of orientation in time and space 
• Loss of spatial awareness and orientation
• Inappropriate social behaviour
• Worsening symptoms late in the evening (sundowning) 
• Aggression, physical violence 
• Hypersexual behaviour 
• Long-term memory impairment, loss of identity 
• Paranoia, delusional beliefs
• Hallucinations
• (Late stage) alogia (little or no speech)
• (Late stage) agitation, restlessness
• (Late stage) incontinence
• (Late stage) immobility
• (Late stage) dysphagia 
• (Late stage) progressive decline in appetite and thirst 
• (Late stage) increasing periods of sleep and unconsciousness 
• (Late stage) loss of autonomic regulation, extremities become cold

There is often a loss of fidelity of the personality. Spouses and family members of dementia patients often report that the patient seems to have become a different person.  

 

Causes of dementia

There are dozens of causes of dementia.

• Alzheimer's disease (AD): the most common cause of dementia.
• Vascular dementia: the second most common cause of dementia.
• Parkinson's disease: These patients usually present with extrapyramidal symptoms. Dementia usually develops late in the course of this disease.
• Parkinson-plus syndromes: This is a group of diseases with similar clinical patterns. These patients often present with extra-pyramidal symptoms and cognitive impairment. They develop dementia much earlier than patients with Parkinson's disease. Includes: 
• Dementia with Lewy bodies (DLB): DLB is the third most common cause of dementia.
• Multiple system atrophy (MSA)
• Progressive supranuclear palsy (PSP)
• Pick's disease
• Fronto-temporal dementia (FTD): This disease leads to preferential destruction of neurons in the frontal and temporal regions. Since the frontal lobe regulates social behaviour, these patients often present with personality changes and socially inappropriate behaviour.
• Normal pressure hydrocephalus (NPH). These patients classically present with incontinence, gait disturbances and dementia.
• Creutzfeldt-Jakob disease (CJD) is an infection which can bring a healthy young person to a state of dementia in a matter of months.

 

Pathophysiology

Sketched illustration of CT scans from 3 patients. View: axial. Left: NPH, Center: FTD, Right: DLB.

NPH: There is an imbalance between CSF production and resorption. Progressively larger volumes of CSF occupy a gradually expanding ventricular system. There is clear ventricular enlargement on the axial view.
FTD: The atrophy is significantly more advanced in the frontal lobes (top of the image). Notice the amount of empty space before the frontal lobes, and the width of the sulci there.
DLB: There is global atrophy with enlargement of the ventricles. The atrophy is not significantly more advanced in one particular lobe.