Clinical Considerations for Patients With Intellectual Disability
Individuals are diagnosed with ID based on intelligence and mental ability and adaptive skills. Compared to individuals free of an ID, people with an ID have a reduced ability to think and solve problems and to adapt and function independently. Once a diagnosis of ID has been made, an individual’s strengths and weakness can be evaluated in order to tailor the amount of support or help needed to function at home, in school, and in the community.
Signs and Symptoms
The major signs and symptoms are usually related to delayed developmental stages in infants and children. This can include delays in sitting up, crawling, and walking. Children may also experience delays in or difficulty with talking. Most developmental milestones are delayed, but the amount of delay depends on the severity and cause of the disability. Later in childhood, a child with ID may have difficulties understanding directions and experience problems with logical thinking and problem solving. It is not unusual for children with ID to be unable to understand social rules or the consequences of their actions (77).
History and Physical Examination
The history and physical examination should follow standard formats. It is likely that a history needs to be acquired from a significant caregiver, as individuals with ID may not accurately remember their history. For people with DS, it important to obtain information on congenital heart disease and any joint problems, such as instability of the atlantoaxial joint (atlantoaxial instability) in the upper neck (i.e., where the base of the skull meets the neck).
Diagnostic Testing
Chromosomal microarrays are being used increasingly as a first-tier genetic test among individuals with unexplained IDs (57). G-banded karyotyping should be reserved for individuals with obvious chromosomal problems or a family history of genetic abnormalities (57). This is a rapidly developing area in relation to ID, and our knowledge and understanding of genetic links to various types of ID will expand substantially in the coming years.
The level of ID is diagnosed through the use of two types of tests: standardized tests of intelligence (e.g., intelligence quotient [IQ] tests) and adaptive behavior (16, 20). The cutoff score used for both is generally 2 standard deviations below the mean for the particular assessment instrument. Well-known IQ tests include the Wechsler Adult Intelligence Scale, Wechsler Intelligence Scale for Children, Stanford-Binet, Woodcock-Johnson Tests of Cognitive Abilities, Raven’s Progressive Matrices, and the Kaufman Assessment Battery for Children. Intellectual disability is diagnosed with an overall score at or below 70 points on most IQ tests. It is important to note that IQ scores are fluid, as intelligence and adaptive behavior can change over the course of a life span, in either a positive or a negative direction. Therefore it is recommended that intelligence and adaptive behavior tests be repeated through the life span.
Adaptive behavioral tests address conceptual, social, and practical skills (16, 20). Conceptual skills have to do with issues of language and literacy, money, time, numerical concepts, and self-direction (16). Skills related to the social being include “interpersonal skills, social responsibility, self-esteem, gullibility, naiveté, social problem solving, and the ability to follow rules, obey laws and avoid being victimized” (16). Lastly, practical skills involve areas related to personal care, travel and transportation, job skills, health care, maintaining a schedule or routine, safety, and using money and the telephone. The AAIDD is slated to release its new Diagnostic Adaptive Behavior Scale in 2012, which will provide a comprehensive standardized assessment of adaptive behavior (16). It will be used with individuals 4 to 21 yr old and provide specific diagnostic information around the cutoff at which someone is deemed to have “significant limitations” regarding adaptive behavior (16). Current tests available include the Woodcock-Johnson Scales of Independent Behavior (used for children), the Vineland Adaptive Behavior Scale, and the 2010 version of AAIDD’s Diagnostic Adaptive Behavior Scale. The Vineland Scale is used for testing social skills in persons from birth through 19 yr of age and is administered to the individual’s caregiver.
A diagnosis of ID is important for several reasons. It establishes eligibility for special education services, home- or community-based services, and Social Security benefits, as well as allowing for special treatment within the criminal justice system. Additional diagnostic tests should be considered for individuals with ID, in particular those with DS. These include tests for hypothyroidism and congenital heart disease, neck X-ray to determine possible atlantoaxial instability, and hearing and vision tests. Individuals with DS have higher rates of infection and respiratory problems; therefore regular blood tests should be performed to detect any abnormalities with the immune system (62, 74).
Exercise Testing
Exercise testing in individuals with ID appears to be largely safe, and safety considerations with respect to cardiovascular complications are likely not different from those for the general population (21, 26). However, it is important to keep in mind that while few reports, if any, exist on exercise-induced complications in persons with ID, there is no body of current scientific evidence to suggest whether exercise testing in this population is indeed safe or not. Certainly this is an area that needs scientific study. Common to a diagnosis of ID is a concern about the person’s ability to follow and understand instructions and cooperate with the testing procedures, which is a concern regarding any type of test in this population. In spite of these concerns, standard laboratory exercise tests appear to be valid in persons with ID (21, 26). Individuals with ID can undergo a full complement of exercise-based tests, which should include tests of aerobic capacity, muscle strength and endurance, and body composition. A summary of exercise testing recommendations is provided in table 32.2.
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