What is the role of dementia scales and assessments in the diagnosis of Alzheimer disease (AD) in Down syndrome (DS)?

Updated: Nov 13, 2019
  • Author: Norberto Alvarez, MD; Chief Editor: Jasvinder Chawla, MD, MBA  more...
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The diagnosis of dementia still is based primarily on clinical history and examination. Generally, the diagnostic methods used for testing persons without developmental disabilities (eg, Mini Mental Status Examination [MMSE] or similar) are unreliable for diagnosing dementia in persons with developmental disabilities. Additionally, many people with developmental disabilities cannot be evaluated by standard neuropsychologic tests.

At present, there is no universally accepted protocol for the diagnosis of AD in persons with intellectual disablity. Guidelines for the diagnosis of dementia, with an accuracy of around 90% in individuals without developmental disabilities have been published by different associations. [96, 97, 98, 99, 100]

However, these diagnostic tests are difficult to apply in persons with developmental disabilities, and several other tests have been designed that are more appropriate. Generally, these tests emphasize a change in function as measured by a decline in activities of daily living (ADLs), such as eating, dressing, and bathing. [101] The use and the validity of these instruments have been extensively discussed. [102]

Some tools that have proved to be very useful [103] are the Dementia Scale for Down Syndrome (DSDS), [104, 105] which was specifically designed to be used in persons with DS, and the Dementia Questionnaire for Mentally Retarded Persons. [106]

The DSDS was developed to detect cognitive deficiencies mostly in persons at the lower end of the cognitive scale; even though the test specifically refers to DS, it could be used in any person with a moderate-to-severe degree of mental retardation. Both the DSDS and the Dementia Questionnaire for Mentally Retarded Persons are able to differentiate, with high specificity and with especially high sensitivity, between persons with DS who have AD and those who do not. [103] There are no major differences between the 2 tests.

Also potentially useful are Part I of the American Association on Mental Deficiency Adaptive Behavior Scale (ABS), the Reiss Screen for Maladaptive Behavior [107] , and the IBR Evaluation of Mental Status (IBREMS).

However, in current practice there is no single battery of tests that can determine the presence of dementia in a person with D.D. developmental disabilities with one single administration. [101] One serious problem in assessing cognitive decline in persons with developmental disabilities is that they already had at least a mild-to-moderate degree of cognitive deficiency before they developed AD. [103] Also, persons with poor education or low-to-moderate cognitive level can be wrongly diagnosed with cognitive decline because of poor performance on the standard tests. [108]

Despite these limitations, there are several tools available that may help to document the diagnosis of dementia in individuals with DS. Because the diagnosis of AD is based on the demonstration of a functional decline, a baseline observation of the individual's cognitive abilities is very important. Sometimes this information can be found in the patient's medical and school records, from family observations, or through direct observation of the patient participating in supervised adult activities. Tests that use caregivers as a source of information may be more reliable than tests directly involving the individual. [101]  

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