Many individuals with Down Syndrome are prone to developing dementia. This relatively new comorbid condition encompasses unknown challenges for clinicians, patients and their carers.
The percentage of people with Down Syndrome who reach adulthood and old age has significantly increased during the past decade. A higher life expectancy reflects a higher quality of life. Nonetheless, this relatively new condition also encompasses unknown challenges for clinicians, patients and their carers. For instance, many individuals with Down Syndrome develop dementia, especially Alzheimer’s Disease. This essay is an attempt to address the complex issue of how dementia presents in people with Down Syndrome.
Dementia is a neurodegenerative clinical syndrome, and its main characteristic is a progressive, gradual decay of previously acquired superior cognitive skills. This decline, higher than the one expected in normal ageing processes, deteriorates daily functionality. Alzheimer’s Disease is the most frequent comorbidity with Down Syndrome. Nevertheless, its clinical presentation may considerably differ from the presentation found in the general population. To comprehend the particular fashion in which dementia manifests in a Down Syndrome context, it is necessary first to examine separately the main characteristics of these two disorders. A brief explanation of the cognitive profile of these neurological illnesses are featured below.
Alzheimer’s Disease (AD), the most frequent type of dementia, has an insidious, progressive, gradual and irreversible course. On the other hand, Down Syndrome (DS), also known as Trisomy 21, is a congenital condition caused by an additional 21 chromosome located in all the cells, or most of the cells, of the patient.
The symptoms that characterise AD are learning and memory decline and disorientation to time and space. DS, on the other hand, is a type of mental retardation, so one of its core characteristics is a moderately to severely impaired IQ, with scores falling within a range of 25 to 55, and a mental age of 7 to 8 years.
Detecting dementia in the Down Syndrome population is a challenging task for clinicians. The premorbid cognitive characteristics of these patients, wide variabilities in their neuropsychological profile, medical and psychiatric comorbidities, the age of onset and different AD manifestations, inconsistency in diagnostic criteria and non-standardized assessment instruments are some of the elements that misguide diagnosis and forward intervention.
Several authors have criticised the lack of consistency of dementia diagnostic criteria when used with people with intellectual disabilities. The standards used in the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) and the International Classification of Diseases (ICD-10) do not consider the premorbid cognitive state of people with DS. Therefore, when comparing this population to the general population, inaccurate diagnosis becomes very common, resulting in many false positive and many false negative cases.
In an attempt to solve this problem, the ICD-10 has established criteria that emphasise non-cognitive aspects of dementia, such as emotional and behavioural symptoms. Moreover, adaptations and revised versions of these manuals have been created. Such is the case of the Diagnostic Criteria for Psychiatric Disorders in Adults with Learning Disability/Mental Retardation (DC–LD) and the Diagnostic Manual-Intellectual Disability (DM-ID). These manuals endeavour to consider the pre-morbid state of intellectual disability, mental and physical comorbidities, and the environmental factors that may influence the diagnosis.
On another topic, physical and mental illnesses are frequent in DS, and they may interfere with assessment and accurate diagnosis. These illnesses include vision and hearing impairment, muscle weakness and motor deficits, cerebrovascular diseases, hypothyroidism, adult-onset seizures, depression, delirium, maladjusted behaviour, obsessive-compulsive symptoms, among others.
Also, it is essential to consider the premorbid cognitive characteristics of DS profiles because assessment should depart from this baseline and not from a comparison of the patient with the normative population. As a consequence of the premorbid state of DS, there is an intense debate surrounding the ways dementia adopts when presented in this comorbid context.
One of the most important characteristics of people with DS is the premature ageing process. Its relevance relies on the evidence that AD manifests at earlier periods, generally between 35 and 40 years of age. Hence, AD in the DS population could be categorised more appropriately as an Early-Onset AD. Overall, this type of AD shows deficits in attention, executive functions, language and praxis.
However, the data yielded by several studies also provides strong evidence that dementia manifests as a Frontotemporal Dementia (FTD) in people with DS, making this condition less understandable. FTD symptoms manifest earlier than in AD, generally at the age of 50 or 60, with cases reported at the age of 20. This condition develops faster than AD, and its core characteristics are deterioration of executive functions, and personality and behaviour changes. Several studies support this hypothesis, and have reported that the first symptoms of dementia in DS patients resemble FTD.
As a rebuttal to these conclusions, other authors support the hypothesis that AD in DS adults does not differ from the AD in the general population.
Other researchers stated that differentiating AD in the average population from AD in the DS population is a complex task for various reasons. They argued that the initial symptoms of dementia might be obscured and are frequently undetected because of the premorbid cognitive deficiencies of this population, and this situation is aggravated when the intellectual disability of the patient is severe or profound. As a consequence, dementia might be detected on its latest phases rather than on its initial stages. Many clinical trials and qualitative studies with carers show that executive functions are the first ones to deteriorate; however, as in the general population, these could constitute signs of later stages in dementia and not of initial symptoms. Finally, the researchers mentioned that the assessment of people with DS is often based on carers’ reports rather than on clinicians’ examinations; but unfortunately, informants’ narratives could be often biased and misguide diagnosis.
The emergence of new pathological conditions constitutes an opportunity to reconsider principles in science that are usually not questioned. Along time, neuropsychologists have intended to quantify mental functions and cognitive deficits using standardised instruments that have strict, standardised procedures of administration. Nonetheless, in an excessive attempt to emphasise the scientific theoretical basis of these protocols, they have neglected the qualitative, subjective factors present in every human being. Dementia and Down Syndrome are just an example of the need to readapt and modify the neuropsychological intervention, considering, not only the quantitative information but also the richness of qualitative, subjective data, highlighting the uniqueness of each case.
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