Both amnesia and dementia are conditions of brain function, but they are two different conditions. Amnesia is only memory loss while dementia features a global loss of higher brain functions. This article will talk in detail about amnesia and dementia and the differences between them, highlighting their clinical features, symptoms, causes, and also the treatment/care they require.
Amnesia is memory loss. Memory loss can be due to head injury, traumatic life experiences, and physical defects of the brain. First two reasons are commoner than the third. It is important to note that certain head injuries can result in physical brain defects. There are many types of amnesia.
Anterograde amnesia features the inability to retain new memories while formed memories are intact. Medial diencephalon and medial temporal lobe deals with new memory formation. Anterograde amnesia cannot be treated by drugs due to neuronal loss.
Retrograde amnesia features an inability to recall memories before the event. There is a time limit to retrograde amnesia. It is usually temporary. Post traumatic amnesia after severe head injury may be retrograde, anterograde or mixed.
Dissociative amnesia is psychological. Lacunar amnesia features loss of memory of a single event. Korsakoff amnesia results from chronic alcoholism.
Dementia features an impairment of all cognitive functions beyond that due to normal ageing. Dementia has a set of symptoms that may be progressive (most commonly) or static resulting from degeneration of the cerebral cortex, which controls the “higher” brain functions. It entails a disturbance of memory, thinking, learning ability, language, judgment, orientation and comprehension. These are accompanied by problems with control of emotions and behavior. Dementia is commonest among elderly individuals where an estimated 5% of the total population above 65 years of age is involved. Currently available statistics estimate that 1% of the population below 65 years of age, 5-8% of people between 65–74, 20% of people between 75-84, and 30-50% of 85 years or older people are suffering from dementia. Dementia covers a broad spectrum of clinical features. Although there are no distinct types of dementia, it can be broadly divided into three according to the natural history of the disease.
Fixed impairment of cognition is a type of dementia which does not progress in terms of severity. It results from some type of organic brain disease or injury. Vascular dementia is a fixed impairment dementia. (Ex: stroke, meningitis, reduction of oxygenation of cerebral circulation).
Slowly progressive dementia is a type of dementia which starts out as an intermittent disturbance of higher brain function and slowly worsens to a stage where there is impairment of activities of daily living. This type of dementia is commonly due to diseases where the nerves degenerate slowly (neurodegenerative). Fronto temporal dementia is a slow progressive dementia due to slow degeneration of the frontal lobe structures. Semantic dementia is a slow progressive dementia which features loss of word meaning and speech meaning. Diffuse Lewy body dementia is similar to Alzheimer’s disease but for the presence of Lewy bodies in the brain. (Ex: Alzheimer’s disease, multiple sclerosis).
Rapidly progressive dementia is a type of dementia which does not take years to manifest itself but does so in mere months. (Ex: Creuzfeldt-Jacob’s disease, prion disease).
Treating any primary disorder, treating superimposed delirium, treating even minor medical problems, involving family support, arranging practical help at home, arrange help for carers, drug treatment and arranging institutionalized care in case of failure of home care are the basic principles of care. Drug treatment is used only when the possible side effects are outweighed by the benefits. In severe behavioral changes such as agitation, emotional instability, occasional use of sedatives is warranted (Promazine, Thioridazine). Antipsychotic drugs may be prescribed in delusions and hallucinations. If depressive features are profound, anti-depressant therapy may be started. Cholinesterase inhibitors acting centrally are of use to approximately half of the patients suffering from dementia due to Alzheimer’s disease. They appear to delay the progression of cognitive impairment and in some cases may even improve symptoms for a time.