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Dementia in Intellectual Disability: a Review of Diagnostic Challenges

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Dementia in Intellectual Disability: a Review of Diagnostic Challenges REVIEW Afr J Psychiatry 2011;14:194-199 Dementia in intellectual disability: a review of diagnostic challenges M Nagdee 1,2 1Fort England Hospital, Grahamstown, Eastern Cape, South Africa 2Department of Psychiatry, Walter Sisulu University, Eastern Cape, South Africa Abstract The 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 and symptoms, (4) results of focused investigations, and (5) refinement of the differential diagnosis. In patients with ID, standard clinical methods need to be supplemented by careful, longitudinal behavioural observations, and individually tailored assessment techniques. Co-morbidity, multiple biological, psychological and socio- environmental factors, and complex interactions among events, are the reality for many ageing people with ID. Determining the various influences is often a formidable clinical task, but should be systematically carried out using medical, cognitive, behavioural, neuropsychiatric and psycho-social frameworks. Key words: Dementia; Intellectual disability; Mental retardation Received: 23-05-2010 Accepted: 09-07-2010 doi: http://dx.doi.org/10.4314/ajpsy.v14i3.1 Introduction Epidemiology People with intellectual disability (ID) [this term is used in Dementia can occur at any age, but is largely a disorder of preference to mental retardation (MR)] are prone to later life. The prevalence of dementia in the general developing dementia in later life. This is particularly population rises markedly with increasing age: from 1-2% in important in the context of rising life expectancies in this people aged 65-69 years, to 16-25% in those over 80 years. 3 population. The average life expectancy of adults with ID (in Among people with ID, dementia is liable to strike more often, developed countries) is 66 years and increasing. 1,2 As these and earlier. A number of community-based studies of ID individuals age, they present with increased rates of physical, populations have yielded age-matched prevalence rates of sensory and cognitive impairments. This results in increasing about 14% in people over 59 years, and 22% in those 65 years health and social care needs, with resultant pressures on and over. 4 The comparative rates among same-age adults carers and support services. Clinicians can expect to come with Down syndrome are much higher, reaching over 40% in across increasing numbers of people with ID who develop those over 50 years, and over 70% for ages above 60 years. 5 dementia as they grow older. Whilst mental health resource priorities in developing countries may be focused elsewhere, Diagnostic criteria people with ID still form a significant, and particularly The diagnosis of dementia in people with ID presents a vulnerable, proportion of our patient population, and have number of challenges 6: been historically neglected in many respects. As • Assessment techniques and tools in common clinical use identification, evaluation, diagnosis, and management of such for the non-disabled population may not be appropriate, patients can be challenging, familiarity with the key issues is especially for individuals with more severe pre-existing essential for all involved in their care. 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 Correspondence • Pre-existing cognitive impairments and disturbances in Prof. M Nagdee Fort England Hospital, P/Bag X1002, Grahamstown, Eastern Cape, behaviour, personality and emotional control may conceal South Africa the often subtle and insidious emergent symptoms of email: [email protected] dementia. 8,9 African Journal of Psychiatry • July 2011 194 REVIEW Afr J Psychiatry 2011;14:194-199 • Some signs of dementia (such as dysphasia, dyspraxia deteriorating course, leading to delays in diagnosis and and agnosia) are often difficult to recognize in people treatment. with ID, particularly in the early stages of the illness. • People with ID have a predisposition to co-morbidity, These criteria have therefore been excluded from which is often severe or frequent enough to influence some ID diagnostic schemes. 10,11 the evaluation and interpretation of their cognitive • Changes in repertoire of adaptive skills or behaviours impairment. may predate any demonstrable early memory • The effects of chronic medication on cognitive function impairments in ID patients. are often overlooked in clinical practice (especially the • The perception, manifestation and degree of functional use of multiple agents). impairment caused by the dementia syndrome largely • There is often a lack of consistent and reliable depends on pre-morbid intellect, level of education and documentation of prior cognitive and adaptive skill training, individual life circumstances, and individual levels, making it difficult to detect decrements until they ability to compensate for newly acquired deficits. 7 become pronounced. • To be indicative of dementia, any changes over time must be greater than those related to normal aging in A comprehensive and focused history from both the patient adults with ID. 7 and multiple informants/sources (e.g. family members, • Neither the ICD-10 nor the DSM IV-TR diagnostic carers, medical records) is usually the most valuable criteria for dementia make any specific mention of diagnostic tool for dementia in ID. The information- ID/MR. gathering exercise aims to: (1) systematically document details of symptoms and functionality, (2) identify treatable To date, there is a lack of consensus on a standardized causes of dementia, and aid in clarifying a working approach to the diagnosis of dementia in ID. As a step differential diagnosis, and (3) conceptualise the current towards such standardization, diagnostic criteria have been problems within a broader pre-morbid and psychosocial proposed by the Working Group for the Establishment of setting, in order to guide appropriate and effective Criteria for the Diagnosis of Dementia in Individuals with management. It is imperative to obtain collateral Intellectual Disability [under the auspices of the information from people who are familiar with the International Association for the Scientific Study of individual’s past behaviour and level of functioning, as well Intellectual Disability (IASSID) and the American as her/his present performance. A clear history of Association on Mental Retardation (AAMR)]. 10 These are declining function may be difficult to elicit in people with largely based on ICD-10 diagnostic criteria (with its more severe ID, where levels of ability may be significantly relatively heavier emphasis on non-cognitive changes in impaired in the first place, or where impairments in dementia). These authors strongly recommend that communication may mask early evidence of decline. dementia should only be diagnosed when longitudinal data Specific enquiry about the presence of risk factors (e.g. demonstrate clinically significant declines in functioning. If family history of dementia, a previous head injury, or some, but not all, of the criteria are met, a diagnosis of vascular morbidity) is equally important. A family history of “possible dementia” is appropriate. This group has further dementia, ID, and neuropsychiatric problems requires proposed a working battery of tests (for both informants special attention. The history should pay particular and patients) for the diagnosis of dementia in adults with attention to previous diagnoses and treatments, especially ID. 8,10 As in the general population, diagnostic certainty will the use of medication. Careful attention should also be paid be enhanced if decline is observed on many tests and to the timing of onset, pattern and progression of across longitudinal assessments. symptoms. Symptoms often have a subtle and insidious evolution (a fact usually more easily appreciated by Clinical features patients and carers retrospectively). Symptoms may, The clinical presentation of dementia among adults with ID however, present abruptly, especially in dementias with (at most levels of disability) is similar to that of adults in the potentially treatable aetiologies. There may be identifiable general population. Nonetheless, there are a number of precipitating factors e.g. a relatively minor physical illness, factors that impact on the clinical evaluation of dementia in a change in environment or following bereavement. The the context of ID 6,12,13,14 , including: history should screen for the presence of pre-existing or • The lack of consensus on what constitutes normal age- co-morbid medical conditions (and their respective related decline in people with ID, and how to treatments). Physical symptoms and signs may also be due distinguish this from dementia. to adverse effects of medication. It is well recognized that • The lower the pre-existing intellectual and adaptive people with ID have a significant predisposition to sensory level of functioning, the more difficult it becomes to impairments, especially hearing and visual impairments evaluate change and document progression. that can be mistaken for, aggravate, be co-morbid with, or • Pre-existing cognitive
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