Dementia in intellectual disability: a review of diagnostic challenges

Abstract

IntroductionPeople with intellectual disability (ID) [this term is used in preference to mental retardation (MR)] are prone to developing dementia in later life. This is particularly important in the context of rising life expectancies in this population. The average life expectancy of adults with ID (in developed countries) is 66 years and increasing. 1,2 As these individuals age, they present with increased rates of physical, sensory and cognitive impairments. This results in increasing health and social care needs, with resultant pressures on carers and support services. Clinicians can expect to come across increasing numbers of people with ID who develop dementia as they grow older. Whilst mental health resource priorities in developing countries may be focused elsewhere, people with ID still form a significant, and particularly vulnerable, proportion of our patient population, and have been historically neglected in many respects. As identification, evaluation, diagnosis, and management of such patients can be challenging, familiarity with the key issues is essential for all involved in their care. EpidemiologyDementia can occur at any age, but is largely a disorder of later life. The prevalence of dementia in the general population rises markedly with increasing age: from 1-2% in people aged 65-69 years, to 16-25% in those over 80 years. 3 Among people with ID, dementia is liable to strike more often, and earlier. A number of community-based studies of ID populations have yielded age-matched prevalence rates of about 14% in people over 59 years, and 22% in those 65 years and over. 4 The comparative rates among same-age adults with Down syndrome are much higher, reaching over 40% in those over 50 years, and over 70% for ages above 60 years. 5 Diagnostic criteriaThe diagnosis of dementia in people with ID presents a number of challenges 6 :• Assessment techniques and tools in common clinical use for the non-disabled population may not be appropriate, especially for individuals with more severe pre-existing levels of intellectual impairment. Diagnosis in the ID population requires a change in status from baseline functioning, not a change from a "normal" level. 7 • Pre-existing cognitive impairments and disturbances in behaviour, personality and emotional control may conceal the often subtle and insidious emergent symptoms of dementia. 8,9Dementia in intellectual disability: a review of diagnostic challenges M Nagdee 1,2 1 Fort England Hospital, Grahamstown, Eastern Cape, South Africa 2 Department of Psychiatry, Walter Sisulu University, Eastern Cape, South Africa AbstractThe evaluation of dementia in individuals with intellectual disability (ID), which will guide subsequent intervention, care and management depends on the systematic review of a number of factors: (1) the individual historical context, obtained from multiple sources, (2) evaluation of the pre-existing cognitive, behavioural, psychiatric, medical and adaptive skill profile, (3) the constellation, and pattern of evolution, of presenting signs a...

Comorbid Conditions in Individuals with Intellectual Disabilities

“…Strydom and Hassiotis (2003) noted the benefits of longitudinal assessment in ID populations given the acknowledged impairment surrounding the interpretation of singular dementia screenings (McDaniel et al 1998). A longitudinal approach may be particularly insightful given the relative dearth of information that has been collected surrounding aging in individuals with ID (Nagdee 2011;Silverman et al 1998).…”

“…Historically neuroimaging procedures have been used predominately to identify the etiology and prognosis of those with dementia (Tartaglia et al 2011). Nagdee (2011 noted that neuroimaging may aid with differential diagnosis but is not always required.…”

“…A decision to use neuroimaging may be related to the observed level of intellectual deficits. In those with severe and profound ID the use of formal diagnostic assessments may be hindered and neuroimaging may be informative (Nagdee 2011). Different neuroimaging processes allow for the analysis of the functional capacity, biochemistry, structure, and metabolic properties (Tartaglia et al 2011).…”

“…For instance, the use of electro-encephalographic readings may not be forthcoming as observed abnormalities may be better related to the primary ID diagnosis (Nagdee 2011). Additional considerations include the presence of preexisting medical conditions, behavioral deficits, and physical abnormalities that may also limit the utility of neuroimaging techniques.…”

CAPs‐IDD: Characteristics of Assessment Instruments for Psychiatric Disorders in Persons with Intellectual Developmental Disorders

“…The SAC characteristics are perfectly suitable for evaluating mental health instruments for the general population, but they do not allow for any IDD‐specific aspects to be considered in the process. Just as the assessment instruments themselves have to be adapted or newly designed to fulfil the specific needs of persons with IDD (Deb & Braganza ; Nagdee ), the sets of characteristics for describing and evaluating them have to be adapted accordingly.…”