5th June 2023

Dementia subtypes

Causes of dementia include:

• Alzheimer’s disease
• Vascular dementia
• Frontotemporal dementia
• Lewy Body dementia
• Normal pressure hydrocephalus
• Creutzfeldt-Jakob disease

Alzheimer’s disease is the commonest cause of dementia, accounting for approximately 60% of cases. The pathophysiology is amyloid plaques and tau tangles in the brain leading to death of the cells affected. Short-term memory is affected first, and the onset is usually insidious. Pharmacological treatment is with cholinesterase inhibitors (e.g. donepezil, rivastigmine and galantamine) which increase the availability of acetylcholine. Adverse effects include stimulation of the parasympathetic nervous system, such as bradycardia, diarrhoea, and hypotension.

Vascular dementia is the next commonest cause, accounting for 10-15% of cases and is due to small strokes in the brain. The history is of a stepwise progression in cognition, and vascular risk factors are usually present.

Frontotemporal dementia (or Pick’s disease) is a neurodegenerative condition in which the frontal and temporal lobes are preferentially affected, giving rise to features of frontal lobe dysfunction such as personality change, impulsive behaviour and difficulty with planning and decision making, as well as impaired memory. It is a common cause of early onset dementia and is also associated with motor neuron disease. Around 10% of patients with frontotemporal dementia go on to develop motor neuron disease.

Lewy body dementia is one of the neurodegenerative conditions associated with parkinsonism. Clinical features include parkinsonism, REM sleep behaviour disorder, hallucinations (which are typically visual and of people, faces and animals) and fluctuating cognition. Patients with Lewy body dementia are particularly sensitive to neuroleptic medications, which can precipitate neuroleptic malignant syndrome. It can be differentiated from Parkinson’s disease dementia by the timing of onset of cognitive impairment in relation to parkinsonism. If the cognitive impairment occurs within a year of the onset of parkinsonism, then the diagnosis is generally Lewy body dementia.

Normal pressure hydrocephalus is an uncommon condition which affects people over the age of 60 years. There is a triad of gait apraxia, urinary incontinence, and cognitive impairment. The cerebrospinal fluid opening pressure is normal, and a non-contrast CT brain may show enlarged ventricles. Symptoms improve with a reduction in cerebrospinal fluid pressure through a therapeutic lumbar puncture. This produces a short-lived improvement in symptoms. A more long-term treatment is a ventriculoperitoneal shunt, but the risks of this neurosurgical procedure in an older frail patient cohort mean that it is seldom performed.

Creutzfeldt-Jakob disease is a prion disease and an uncommon cause of rapidly progressive dementia. It is universally fatal, usually within one year. There are four types:

• Sporadic – this is the most common type
• Variant – caused by consuming meat from a cow with bovine spongiform encephalopathy
• Familial – rare
• Iatrogenic – previously caused by growth hormone treatment using human growth hormones from infected individuals. This is very rare now.

Clinical features include rapidly progressive dementia, ataxia, myoclonus, and psychiatric symptoms. Diagnosis is confirmed by electroencephalogram with characteristic periodic sharp waves, demonstrating the abnormal 14-3-3 protein in cerebrospinal fluid, from brain biopsy or at autopsy.