Aetiology

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Diagnostiek van dementie in de huisartsenpraktijkPublished by: ACHG | Expertisecentrum Dementie VlaanderenLast published: 2020Diagnostic de la démence en médecine généralePublished by: ACHG | Expertisecentrum Dementie VlaanderenLast published: 2020

A thorough history and physical examination, supported by appropriate investigations, are essential to differentiate dementia from mild cognitive impairment and normal ageing. It is important to consider the aetiology of dementia syndrome because an estimated 11% to 14% of cases are caused by potentially reversible conditions.[11][12]​​ A number of conditions can present in a similar way to dementia syndrome and must be considered during the evaluation. These include delirium, depression, amnestic syndromes, aphasia, and normal ageing.

Modifiable lifestyle factors such as smoking, midlife obesity, a diet high in saturated fats, and consumption of >14 units of alcohol/per week have been associated with an increased risk for the development of dementia.[13][14][15][16]​​​ Other potential risk factors include traumatic brain injury, hearing and vision loss, and high cholesterol.[15][17][18][19][20][21]​​

Prompt and thorough cognitive assessment quantifies the memory deficits and ensures appropriate diagnosis and management.[22][23]

Drugs such as acetylcholinesterase inhibitors (e.g., donepezil, rivastigmine, galantamine) and memantine (an N-Methyl-D-Aspartate [NMDA] receptor antagonist) can temporarily improve dementia symptoms and slow cognitive impairment in some patients.[23] [ Cochrane Clinical Answers logo ]

Mild cognitive impairment (MCI)

MCI is defined as a condition characterised by cognitive decline to an extent that is beyond that expected for age or educational background, yet not causing significant functional impairment.[24]​ MCI is conceptualised as a transitional state between the cognitive changes of normal ageing and very early dementia. 

Once the diagnosis of MCI is established, the next task is to identify the clinical subtype. There are two subtypes of MCI, amnestic and non-amnestic.[25] Patients with memory impairment (taking into account age and education) have amnestic MCI. If memory is relatively spared, but the person has impairment in other non-memory cognitive domains, such as language, executive function, or visuospatial skills, this constitutes non-amnestic MCI.[24]

Patients with amnestic MCI typically progress to Alzheimer’s disease at a rate of 10% to 15% a year. These progression rates far exceed the population incidence figures for Alzheimer’s disease of 1% to 2% a year.[26]

Degenerative and vascular

The majority of cases of dementia have degenerative and vascular causes.[10] More than one cause may be contributing to the dementia syndrome.

Degenerative causes

Include Alzheimer's disease (the most common cause of dementia accounting for an estimated 60% to 70% of cases), Lewy body disease, Parkinson's disease, frontotemporal atrophy with and without Pick bodies, Huntington's disease, progressive supranuclear palsy, and spinocerebellar degeneration.[27] The disease entity limbic-predominant age-related TDP-43 encephalopathy (LATE) has been described.[28] LATE neuropathological change (LATE-NC) is defined by a stereotypical TDP-43 proteinopathy in older adults, with or without coexisting hippocampal sclerosis pathology. It is associated with an amnestic dementia syndrome that mimicked Alzheimer’s-type dementia in retrospective autopsy studies, and is distinguished from frontotemporal lobar degeneration with TDP-43 pathology based on the relatively restricted neuroanatomical distribution of TDP-43 proteinopathy and its epidemiology (LATE generally affects older subjects).[28]

Vascular causes

Account for 5% to 20% of dementia cases.[10][29]​ Vascular dementia includes dementia due to multiple infarcts, a strategic single infarct, haemorrhage, hypoperfusion, delayed effects of irradiation, vasculitic disorders involving the central nervous system, cardiac disorders, and Binswanger's disease.[30][31][32]​ Binswanger's disease, also called subcortical vascular dementia, is caused by widespread microscopic areas of damage to the deep layers of white matter in the brain. It is a pathological diagnosis and a rare cause of vascular dementia.

Psychiatric

Psychiatric causes of memory problems include delirium, depression, and amnestic syndromes.

Dementia and depression may coexist, and depression increases the 5-year risk of institutionalisation and death in people with dementia.[33] Over 25% of patients with neurodegenerative disorders receive a prior psychiatric diagnosis, most frequently depression. Patients with severe isolated memory loss have an increased risk of developing dementia and should be closely monitored.[34]​ Patients with behavioural variant frontotemporal dementia are at highest risk for misdiagnosis.[35]

Neoplastic

Neoplastic causes include metastatic lesions of the brain, primary brain tumours, primary meningeal tumours, and carcinomatosis.

Endocrinological, metabolic, and nutritional deficiency

Related causes include vitamin B12 or folate deficiency, Cushing's disease, hypopituitarism, parathyroid disease, porphyria, thyroid disease (hypo- or hyperthyroid state), uraemia, and Wilson's disease.

Traumatic

Causes include subdural haematoma and traumatic brain injury hypoxaemic anoxia. Patients with head trauma may develop memory problems, although the link between head injury and dementia is controversial.[17]​[36][37]​​

After human brain injury, both amyloid beta peptide deposition and tau pathology (in which tau protein, a microtubule-associated protein, accumulates as neurofibrillary tangles and dystrophic neurites) are seen, even in younger patients.[38][39]​​ Amyloid beta peptide levels in the cerebrospinal fluid and the overproduction of beta amyloid precursor protein in humans after traumatic brain injury are increased. Repeated head trauma in humans accelerates the amyloid beta peptide accumulation and cognitive impairment. Retrospective autopsy data support clinical studies suggesting that severe traumatic brain injury with long-lasting morphological residuals are a risk factor for the development of dementia.[36]

Infectious

Causes include Lyme disease, neurosyphilis, and tuberculosis meningitis. There has been an increase in cases of syphilis in low- and middle-income countries and in certain populations in developed countries in recent years, but the diagnosis of neurosyphilis tends to be overlooked because of its rarity.[40]

Creutzfeldt-Jakob disease (CJD) is a rare but fatal neurodegenerative disease caused by infectious proteins called prions. It is characterised by spongiform changes, neuronal loss, reactive astrocytic proliferation, and accumulation of pathological cellular protein.[41] CJD occurs in three general forms: sporadic or spontaneous, genetic or familial, and acquired (iatrogenic). A variant form of CJD (vCJD) is associated with eating meat from cattle affected by bovine spongiform encephalopathy. CJD is a rapidly progressive dementia, with death usually resulting from respiratory infection.[41]

Inflammatory

Causes include demyelinating diseases, lupus erythematosus, sarcoidosis, Sjogren's syndrome, and limbic encephalitis.

Iatrogenic

Drug-related causes include use of antihistamines and anticholinergics.[42][43][44]​​ Some authors report increased risk of dementia with use of benzodiazepines and other sedative/hypnotic drugs in a dose dependent fashion, but this needs further investigation.[45][46][47][48]​​​​​ There is some evidence that androgen deprivation therapy in men and oestrogen-only hormone therapy in women may be associated with an increased risk of dementia; further investigation is required.[49][50]

Toxic

Alcohol, heavy metals such as arsenic, lead, and mercury, histotoxic anoxia due to carbon monoxide, and cyanide are possible causes.[51]

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