(all causes) 2 % @ 65 yrs
33% >85 yrs 100% progressive loss of two or more intellectual functions (e.g. memory, language), sufficient to disrupt daily life Alzheimer’s disease 1.5% @ 65 yrs
commonest cause of dementia in later life 60% core feature is usually poor day-to-day memory, language and visuospatial function Vascular dementia 0.5% @ 65 yrs 20-30% usually a history of stroke with physical signs such as limb weakness & dysarthria: cognitive impairment may take many forms Frontotemporal dementia less common than AD but an important cause of young-onset dementia: accounts for up to 20% of patients with dementia aged 45-65 years (HIV excluded) <10% frontal: insidious changes in personality and behaviour, other domains often intact temporal: progressive aphasia, fluent or non-fluent HIV associated dementia 10-20% of patients with advanced HIV not-known non-specific: generalised cognitive and motor slowing with poor day-to-day memory Dementia with Lewy bodies less common <1% parkinsonism, fluctuations, visual hallucinations

* based on high income countries

Main causes of dementia in Africa

Risk factors

The main known risk factors are old age, genetic predisposition (e.g. APO-E genotype) and vascular risk factors such as hypertension, hypercholesterolaemia and diabetes. Diet, lifestyle and lower level of education may also be risk factors. At present there are no known specific preventatives or curative measures for most forms of dementia.

General course and prognosis in dementia

By definition, dementia is a progressive disorder. Consciousness is not altered, but with time impairments of higher function extend into all cognitive areas (see appendix 1). The level of functioning declines until patients are entirely dependent on others for their care. Death follows either directly from the failure of core brain systems or more often as a secondary consequence of complications such as pneumonia, untreated pressure sores and venous thrombosis. The duration and course of dementia depends on the cause but typically lasts for years. Life expectancy in Alzheimer’s disease is about 6-7 years from onset in high income countries.

ALZHEIMER’S DISEASE

Alzheimer’s disease is the commonest cause of dementia worldwide (Table 17.1). It is reported to be less common in Africa as compared to similar aged populations in high income countries, including Afro-Americans. However studies from Africa suggest that it still accounts for >60% of all cases of dementia there. Its main cause is unknown. It is rare under 45 years of age but thereafter its prevalence rises exponentially with age and increasingly after 65 years of age. It is associated with a positive family history of dementia and affects females more than males.

Genetics

Alzheimer’s is usually a sporadic disease, but can occasionally be familial when it is autosomal dominant, due to mutations in the genes for presenilin 1 & 2 (PS1 & 2) or amyloid precursor protein (APP) on chromosome 21.The majority of familial AD is caused by mutations in PS1, which usually results in very early onset disease (under 45 years) with rapid progression and additional physical signs. Apolipoprotein E (APOE e4), a lipid transport protein which has been identified as an independent risk factor for AD appears not to influence AD progression in SSA.

Pathophysiology

It is due to loss of neurones from the cerebral cortex and is associated with characteristic deposition of beta-amyloid plaques and neurofibrillary tangles in the neurones. This results in decreased acetylcholine synthesis in the brain.

Clinical features

The clinical features range from mild cognitive impairment with an isolated difficulty in day-to-day memory or forgetfulness, followed by slow progression over years to a severe loss of other cognitive functions, including recognition, language and visuospatial awareness. Loss of memory for recent events and recent personal experiences are typical. Behaviour and personality are often well preserved to begin with, and the diagnosis can be overlooked in the early stages. Physical signs appear later in the disease, when patients may develop parkinsonism, myoclonus and incontinence.

Diagnosis

The diagnosis is made by a careful history from the patient and an informant, supported by objective evidence of cognitive impairment on bedside tests. A Mini Mental State Examination (MMSE) (see appendix 2) score of 24/30 or less is supportive of a diagnosis of dementia, having excluded other secondary causes of dementia with appropriate blood tests and brain imaging.

Investigations

The main investigations in dementia are outlined in Table 17.2. The main aim is to exclude a treatable cause e.g. B-12 deficiency or HIV.

Management

There is no cure at present for Alzheimer’s disease. Non drug interventions are the mainstay of management. This includes the provision of information and support for the carer’s family and the community. One aspect of the disease is a deficiency of acetylcholine synthesis in the brain, and centrally acting cholinesterase inhibitors that raise levels of acetylcholine in the brain may result in temporary symptomatic benefit. In high income countries, the cholinesterase inhibitors are recommended for patients with mild to moderate dementia (MMSE range 12-24/30). Patients may derive some limited benefit in cognitive function for 1-2 years but there is no effect on the eventual progression of the disease. These are stopped if the MMSE score is <12/30.

Drug options include the cholinesterase inhibitors donepezil 5-10 mg daily or rivastigmine 1.5– 3 mg bid, or galantamine 4-6 mg bd. The main side effects are related to increased peripheral cholinergic activity and include nausea, abdominal colic and diarrhoea. However the high cost of the regular use of these drugs prohibits their widespread use in AD in Africa. For behavioural and psychiatric disorders, it may be necessary to use an antipsychotic medication. These include haloperidol 0.5-1.5 mg twice daily. Alternatives include risperidone 0.5 mg or olanzapine 2.5 mg/po daily initially. Valproic acid may decrease agitation and help as a mood stabilizer and be better tolerated than the antipsychotics. It is wise to start with low doses and adjust any increases in dosages slowly.

Key points

Related posts:

COMA AND TRANSIENT LOSS OF CONSCIOUSNESS MYOPATHIES AND MYASTHENIA GRAVIS PARAPLEGIA NON TRAUMATIC HEAD AND SPINAL INJURY NEUROLOGICAL ILLNESS IN HIV DISEASE DISORDERS OF PERIPHERAL NERVES

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