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Dennis van de Veen, Christian Bakker, Tor Rosness and Raymond Koopmans
Key points
- An unequivocal definition and nomenclature for young people living with dementia are lacking. Given the large differences in psychosocial and biological characteristics of these younger people living with dementia, more clarity about these aspects is needed.
- Numerous terms have been suggested, each with different pros and cons, such as the inclusion of a broader variety of aetiologies or terms that introduce semantic ambiguity.
- In the distinction from late onset dementia, different age-related criteria are open for debate, such as an ideal cut-off age and whether or not to look at age at symptom onset or age at diagnosis.
- In the large heterogeneity of aetiologies observed, a part of this heterogeneity is caused by the inclusion of somewhat controversial conditions as a cause of dementia at a young age.
Introduction
Currently, nearly 50 million people live with dementia worldwide (Alzheimer’s Disease International, 2013). The group of people living with dementia also includes younger people with dementia. However, no univocal understanding exists of the nomenclature and definition of this condition, especially with regard to the age of symptom onset, i.e. when should a person diagnosed with dementia be considered young. In the current literature, various terms are in use that can be considered ambiguous when describing individuals who develop dementia at a young age. Different criteria are also used to distinguish this group from those living with dementia in old age (Koopmans & Rosness, 2014). Therefore, it is important that the scientific community agrees upon criteria concerning younger individuals who develop dementia – including cut-off age, rate of cognitive and functional decline or prognosis of the disease.
Young people living with dementia often still have active lives and various roles to fulfil in society at the time of onset of the disease, such as being a spouse, parent and financial provider for the family (Kaiser & Panegyres, 2006). Consequently, dementia at a young age can result in problems at work, unemployment, financial difficulties, marital problems, changes in role patterns within the family and a reduction in well-being (van Vliet et al., 2013). These changes also lead to specific unmet care needs that differ from the care needs of people living with dementia in old age (Bakker et al., 2010). Consensus about the nomenclature and clinical definition is an important prerequisite for scientific research in the field of dementia at a young age and will also aid the implementation of research findings. In this chapter, an overview of the challenges concerning the lack of consensus about these particular aspects will be considered, together with a summary of the background to this topic and goals for future work.
The prevalence of young onset dementia
In order to develop appropriate healthcare services and support and allow for a fit with the care needs of young people living with dementia, it is necessary to gain insight into the number of people that are currently living with dementia at a young age, and how many people who display symptoms of young onset dementia but have not yet been diagnosed (Harvey et al., 2003). Few population-based studies on the epidemiology of young people living with dementia exist, making it difficult to accurately estimate the rate of the potential mismatch between people in need of care and the amount of services available. Based on the few existing studies, the prevalence of dementia at a young age can be estimated between 68.2 and 85.5 per 100.000 people (Kvello-Alme et al., 2019; Withall et al., 2014) although these numbers will vary within countries around the world. Both studies furthermore suggest heterogeneity of aetiologies – causes of dementia – in which frontotemporal dementias and alcohol-related dementias show relatively high prevalence rates in comparison with these particular subtypes in late onset dementia.
Nomenclature
In literature, various terms are used to describe younger people living with dementia. In this section, a chronological overview will be given on the existing terms, their origin and the advantages and disadvantages of the use of these terms.
The term presenile dementia, first introduced by Alois Alzheimer, is derived from a case of dementia in which a 51-year old patient – Auguste D. – showed signs of senile dementia (Graeber et al., 1997).
This term is now regarded as outdated (Rossor et al., 2010) because it does not reflect all possible aetiologies of dementia (Miyoshi, 2009). Although some aetiologies occur in both older and younger individuals, some of these aetiologies, such as frontotemporal dementia or metabolic disorders, predominantly or even exclusively occur at a young age.
A PubMed search with the term early onset dementia shows that this term has been applicable for approximately two decades. Early onset dementia includes the more common aetiologies that have their onset at a younger age, as well as the typical old-age aetiologies such as Alzheimer’s disease and vascular dementia (Miyoshi, 2009). Furthermore, the clinical manifestation of Alzheimer’s disease can often show atypical symptoms when occurring at a young age, such as the absence of episodic memory dysfunction and the presence of apraxic or aphasic symptoms (Balasa et al., 2011). A short-coming of the term early onset dementia is that it may be easily confused with the term early-stage dementia, used to refer to the stage or phase of the dementia.
The term young onset dementia refers to the fact that the onset of dementia occurs at a relatively young age, which is relevant since most cases of dementia occur at an old age. According to Kuruppu and Matthews (2013), this particular term encompasses aetiologies that occur typically in both young and old individuals, as well as late onset forms of childhood neurodegenerative disorders such as mitochondrial disorders and leukodystrophies, suggesting that the use of this term is less restrictive and would allow for the inclusion of a broader variety of aetiologies compared to the term early onset dementia in light of the scientific literature readily available.
A more recently introduced term in countries like Australia is the term younger onset dementia (Sansoni et al., 2016). Although this term appears to aim at underlining the distinction from late onset dementia, clarity might be reduced due to the assumed comparison, which is embedded in the name. The question that arises from this term is: ‘younger than who?’.
There have been some explicit discussion among researchers about a term of preference, for instance, during the 2011 meeting of the Early onset dementia taskforce of the International Psychogeriatric Association (IPA) in The Hague. The taskforce agreed upon using the term young onset dementia for all young people living with dementia (Koopmans & Rosness, 2014). This taskforce is currently known as the Shared Interest Forum Young Onset Dementia.
Age
In scientific literature, different age criteria are used to distinguish younger individuals from those with late onset dementia, and the age of 65 years appears to be most commonly used. This is most likely related to the pragmatic fact that the retirement age is set at 65 years in most countries. Young onset dementia is characterized by different psychosocial consequences that are distinct from those in late onset dementia and directly related to living an active life and being still employed. From this perspective, a cut-off age related to retirement age would seem natural.
Alternatively, considering disease biology, disease subtypes for young onset dementia have a larger biological variability compared to those in old age (Kelley et al., 2008). A broader range of aetiologies is seen and clinical symptoms often differ, e.g. a distinct cognitive profile and more intact disease awareness in young individuals with Alzheimer’s disease compared to older individuals with the same disease (Balasa et al., 2011; van Vliet et al., 2013). Rare aetiologies, such as metabolic disorders, more commonly occur well before the age of 60 years. Therefore, as an alternative to a psychosocial perspective, in which retirement age is used as a cut-off criterion, the ages with the highest prevalence for rare aetiologies could be used to distinguish young from late onset dementia. From this biological perspective, young onset dementia could be considered as dementia occurring, for example, before age 45 or 60 years. This would also be arbitrarily chosen as there are limited cohort studies to support this view.
Reasoned from another biological perspective, typical problems in the elderly, such as frailty, are arguably more common in people aged 70 years and over, defining them as a different population. Thus, the age of 70 years as a cut-off age could be adopted as the cut off age. It follows that, regardless of methodology, the cut-off age will either way largely impact both the incidence and prevalence of dementia at a young age.
Furthermore, if using age to define young onset, there is no consensus about whether this should be age at symptom onset or age at diagnosis. Initial symptom onset would be the closest to the actual biological onset of dementia, but a disadvantage in this use is that it relies upon subjectivity, often from the next of kin (Kaiser & Panegyres, 2006). Thus, although these subjective estimations give a better insight into the age at the dementia onset, the actual onset of dementia remains uncertain. Ample evidence suggests a disease onset long – perhaps several years or even decades – before the first symptoms are noticeable, for example, in Alzheimer’s disease (Apostolova & Cummings, 2008). In dementia with Lewy bodies, nocturnal behavioural problems might even be present a decade before other cognitive symptoms occur (McKeith et al., 2017).
Theoretically, the age at diagnosis can be established more objectively, but a disadvantage of the use of age at diagnosis as a cut-off criterion is that it, most likely, misses the actual onset as, on average, a delayed diagnosis of 4.4 years after symptom onset is present (van Vliet et al., 2013).
In the literature, several authors propose that a lower age limit should be used (Kelley et al., 2008; Rossor et al., 2010) since a minimum age would distinguish developmental disorders from neurodegenerative disorders more clearly. When considering dementia as a neurodegenerative...
