Dementia – definition and etiology

Dementia is among the top 10 diseases across the world and is the only disease on the list that cannot be prevented, treated or slowed down in a significant way (22). Norway uses the International Statistical Classification of Disease and Health Related Problems (ICD-10) from the World Health Organisation (WHO) to report diagnoses to the Norwegian Patient Registry and to define diseases and disorders (23). According to the updated ICD-11, which will eventually replace ICD-10, dementia is defined as an acquired brain syndrome that causes a progressive decline of cognitive functions from previous levels. For a person to be diagnosed with dementia, the individual must have a lasting impairment within two or more cognitive domains. These cognitive domains are memory and learning, attention, language, social cognition and judgement, visuospatial abilities, executive functions and psychomotor speed. In addition, dementia is excluded if the decline stems from altered mental status, disturbed consciousness, delirium, substance use or other mental and behavioural conditions that affect the brain. Dementia is not a part of normal aging and significantly interferes with normal activities in daily life and independence (24).

There are different subtypes of dementia depending on etiology, which cognitive domain is affected and the severity of symptoms (25, p. 591). However many of the symptoms are the same for the different subtypes and the people who are affected deal with similar problems in their lives (25). There are multiple causes for the syndrome which generally can be divided into neurodegenerative and non-neurodegenerative origin. Neurodegenerative dementia is caused by irreversible damages to the neurons in the brain. Non-neurodegenerative dementia is caused by other factors, such as cerebrovascular disease, traumatic brain injuries, chronic substance abuse etc. Physicians can detect characteristic changes in the brain through a magnetic resonance imaging (MRI) to diagnose dementia subtypes (26). It can be challenging to diagnose people with a subtype, since the symptoms can be similar and people can be diagnosed with multiple subtypes (26). However, it is useful to understand the common subtypes because we can then understand the symptoms better. Here is a short presentation of the most common

Alzheimer´s disease (AD) is the most common type of neurodegenerative dementia (26).

According to the Norwegian prevalence report by Gjøra et.al., around 57% of PWD in Norway have AD (4). AD is a neurodegenerative subtype and is characterized by a slow and gradual accumulation of amyloid plaques and intraneural neurofibrillary tangles (NFT) in the brain. The amyloid plaques and NFT damages the neurons in the brain and disrupt neuronal function (27).

Typical symptoms include slowly progressing memory loss early on in the disease course, in addition to other signs such as irritability, apathy and low mood. As the disease progresses, the patient can begin showing behavioural, visuospatial and language disturbances are frequent. In addition, their judgment might become impaired and confusion and disorientation is common (26, 28).

Vascular dementia (VD) is the second most common dementia in Norway, around 10% of those with dementia according to Gjøra et. al. (4). Vascular dementia is triggered by a cerebrovascular injury in the brain, such as ischemic or hemorrhoidal stroke, and is classified as a non-neurodegenerative subtype. There are several modifiable risk factors which can lead to the person developing a vascular cognitive impairment, such as hypertension, hypercholesteremia, diabetes and smoking. In addition, risk factors for stroke such as coronary heart disease, atrial fibrillation and myocardial infarct also increases the probability of a vascular cognitive impairment (26). Unlike AD, which causes a gradual and progressive cognitive decline (usually over many years), people with vascular dementia can have an abrupt cognitive decline following a stroke. Alternatively, the cognitive decline can appear more gradually and plateau within a few weeks to months after the stroke. The cognitive decline manifests within a relatively short time period after a cerebrovascular incident and symptoms can be slow speed, subtle speech changes, memory loss and apathy, depending on the region affected and the severity of the stroke (26).

Mixed dementia, mostly with parallel AD and VD processes, is thought to be more common among those aged ≥ 85 years (27). Around 9% of PWD in Norway have a mixed dementia diagnosis according to the prevalence report from Gjøra et. al. (4). The diagnosis can be set if a person has signs of AD and later on experiences a stroke that worsens the cognitive decline.

(26, 27).

Dementia with Lewy Bodies (DLB) and Parkinson’s disease with Dementia (PD) are neurodegenerative dementias with similar symptoms. It is estimated that around 4% of PWD are diagnosed with these subtypes in Norway according to the Norwegian prevalence report (4). However, DLB and PD are probably underdiagnosed among PWD (29). A study from UK showed that 4.6% of PWD had DLB alone, while a meta-study estimated around 3.5% of PWD had PD (30). The cognitive impairment is caused by an accumulation of Lewy bodies, a synaptic protein consisting of alpha-synuclein, in neurons (26). Common clinical symptoms for DLB are cognitive fluctuations, visual hallucinations and features from parkinsonism (limb ridgidity, tremor at rest, slow movements, etc.). Memory loss and spatial difficulties can be less prominent compared to other dementia subtypes. In PD has also an accumulation of Lewy bodies and similar symptoms are also observed, however the subtype of DLB or PD is diagnosed based on time of onset. If the cognitive symptoms debut at least 1 year after being diagnosed with Parkinson’s disease, then the person is diagnosed with PD rather than DLB (26).

Frontotemporal dementia (FD) is a group of neurodegenerative dementias that are caused by a selective degeneration of the frontal and temporal lobes of the brain. It is estimated that around 2% of PWD have this subtype according to Gjøra et. al. (4, 26). Symptoms of frontotemporal dementia are dependent on which region of the brain is affected. Patients with the behavioural variant often shows symptoms such as personality changes, lack of inhibition and loss of executive functions. Other types of FP can have progressive aphasia, parkinsonism, frequent falls and behavioural changes as prominent symptoms (26).

The cognitive decline and symptoms makes PWD a vulnerable group. The majority of PWD are elderly and therefore prone to age-related issues. Dependent on the dementia subtypes, the symptoms could make it difficult for PWD to understand and express themselves when receiving treatment. This can lead to them having a higher chance of receiving inappropriate treatment, and increase the risk of drug-related injuries. Other PWD might not receive treatment at all, which is also a health issue for the PWD (31, 32).