Early onset dementia

Early onset dementia or young onset dementia refers to dementia with symptom onset prior to age 65. This condition is a significant public health concern, as the number of individuals with early onset dementia is increasing worldwide.^[1]

Early onset dementia is a general term that describes a group of conditions featuring progressive cognitive decline, particularly in the domains of executive function, learning, language, memory, or behavior. This condition may occur due to various different causes, including degenerative, autoimmune, or infectious processes. The most common form of early onset dementia is Alzheimer's disease, followed by frontotemporal dementia, and vascular dementia, with Alzheimer's disease accounting for between 40 and 50% of cases.^[2][3] Less common forms of early onset dementia include Lewy body dementias (dementia with Lewy bodies and Parkinson's disease dementia), Huntington's disease, Creutzfeldt–Jakob disease, multiple sclerosis, alcohol-induced dementia, and other conditions.

The term young onset dementia is becoming more widely used to avoid the potential confusion between early onset dementia and early stage dementia This term is now used as presenile dementia which is a historical term of people diagnosed with dementia from a younger age of 51 years old. This is caused by an atypical arterioclerosis of the brain. Although these terms can be exchanged during the course of literature it can cause misunderstandings between the subgroups of a younger crowd living with dementia. Additionally terminology recent research has focussed on the different age groups of dementia and how they differ from one another. Studies have found there is a greater diversity within younger people who have dementia compared to older patients. Evidence have been found on Alzheimer's disease causes in the brains of young people which can result in phenotypic variants compared to older people. Which explains why younger people with Alzheimer's disease have more awareness than older individuals.^[4][5]

Early onset dementia is less common than late onset dementia, the former accounting for approximately 10% of dementias globally.^[3] Recent studies estimate the prevalence of early onset dementia to be approximately 3.55 million people aged 30–64 worldwide, and will triple by 2050.^[6] with an incidence of 119 per 100,000 individuals.^[1] Additionally, there is approximately a 1:1 ratio in prevalence of Early onset dementia between males and females, with no significant difference between ethnic groups in gender distribution pattern.^[7][8] Similar to late onset dementia, the prevalence of early onset dementia increases exponentially with age, doubling every five years of age.^[7] The continuous increase in prevalence with age seen in Alzheimer's and frontotemporal dementia versions of early onset dementia is disproportionally led by the most common variant of each cause, namely amnestic Alzheimer's and behavioral variant of frontotemporal dementia.^[9]

Traditional risk factors for the development of late onset dementia, such as diabetes mellitus, hypertension, and obesity, have also been identified as risk factors for early onset dementia. Several other chronic conditions have recently been identified that are also associated with the development of early onset dementia, including cardiovascular, respiratory, or gastrointestinal disease.^[10] The presence of one or multiple of these chronic conditions is more predictive of early onset dementia compared to late onset dementia.^[10] Furthermore, the association between low socioeconomic status and the development of dementia is also more pronounced in early onset dementia compared to late onset dementia.^[11] Additionally, depending on the etiology of early onset dementia, family history may be a significant risk factor, especially for Alzheimer's early onset dementia.^[8] Additionally it is more common for women to be diagnosed with Alzheimer's disease compared to men, for men it is more common to conduct vascular dementia. Studies have shown men will less likely develop Alzheimer's disease.^[12]

Though widely accepted, the definition of early onset dementia as less than 65 years of age continues to be an artificial cut-off based on the traditional retirement age in most countries.^[13] Nevertheless, the purpose of having a specific age cut-off is evidenced in the significant differences in the etiology and prognosis of dementia depending on the age category of the patient. Furthermore, the diagnosis of early onset dementia continues to be challenging due to the wide range of symptoms at presentation and increased likelihood of not considering neurodegenerative causes in this population. Recent studies indicate an average of 4.4 years time to diagnosis for early onset dementia, compared to 2.8 years for late onset dementia.^[7] Indications for the work-up of early onset dementia in this patient population include progressive, unexplained neurological symptoms; new-onset behavioral changes inconsistent with previous personality, especially in patients without significant psychiatric history; or cognitive changes in patients with significant family history of early onset dementia.^[14] The diagnostic work-up of early onset dementia includes combinations of detailed history taking, neuroimaging, behavioral testing, and genetic testing.^[14] Special considerations for interdisciplinary support should be pursued for younger patients, such as behavioral counseling, social services, or home modifications. The World Health Organization promotes the importance of rehabilitation services (including cognitive, psychological, physical and social support) to improve the quality of life of those with dementia.^[15] Despite this specific services for those with early onset dementia are rare.^[16] The integration of age-appropriate services into existing dementia care, and the use of telehealth have both been explored as options for reducing cognitive disability, and improving quality of life, in early onset dementia.^[16]

Compared to late onset dementia, patients with early onset dementia are more likely to have dementias other than Alzheimer's disease, although Alzheimer's is the most common etiology in either case.^[13] In general, early onset dementia has a faster progression and features more extensive neurological damage when compared to late onset dementia. It is hypothesized that this may be due to decreased cognitive reserve seen in late onset dementias, causing more significant complications relative to pathological damage.^[13] Furthermore, studies have shown differences in the areas of cognition that are likely to be affected when comparing early onset to late onset dementia. In terms of behavioral symptoms, early onset dementia is more likely to affect attention, but less likely to cause confusion, delusions, hallucinations, agitation, or disinhibition. In terms of motor symptoms, early onset dementia is less likely to affect verbal fluency and motor executive function compared to late onset dementia.^[13]

Estimation of survival rate in early onset dementias is a component patient prognosis, management, and treatment. In general, a better prognosis is positively correlated with earlier age of onset.^[13] Average survival time is approximately 6–10 years following diagnosis for both men and women, with variability depending on specific type of dementia.^[7] The most common cause of immediate death in early onset dementia is respiratory disease (e.g. pneumonia); other causes include cardiovascular events and cerebrovascular disease.^[13]

• Childhood dementia
• Early-onset Alzheimer's disease

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