CHAPTER TWO
2.3 Intellectual disability
2.3.3 Classification of intellectual disability
2.3.3.2 DSM-IV-TR classification
This presents the standard classification approach in the US, and defines mental retardation (intellectual disability) as a significant sub-average general intellectual functioning that is accompanied by significant limitations in adaptive functioning in at least two of the following skill areas: communication, self-care, home living, social/interpersonal skills, use of community resources, self-direction, functional academic skills, work, leisure, health, and safety. The onset must occur before the age of 18 years.
Like ICD-10, the definition specifies that intellectual functioning is defined by the IQ obtained through assessment with one or more of the standardised, individually administered intelligence
38 tests. Significantly, a person with sub-average intellectual functioning is defined as having an IQ of approximately 70 or below (about two standard deviations below the mean). This must be accompanied by significant deficits in adaptive behaviour for intellectual disability to be diagnosed. Factors that may affect test performance, such as socio-cultural background, native language, and associated communicative, motor and sensory handicaps, must be considered when choosing testing instruments and in interpreting results.
Codes based on degrees of severity that are similar to those presented in ICD-10 are specified by DSM-IV-TR:
317 Mild mental retardation IQ 50-55 to approximately 70 318.0 Moderate mental retardation IQ 35-40 to 50-55
318.1 Severe mental retardation IQ 20-25 to 35-40 318.2 Profound Mental Retardation IQ below 20 or 25
319 Mental retardation, Severity Unspecified: when there is a strong presumption of mental retardation but the person‘s intelligence is untestable by standard tests
The DSM-IV-TR uses a multi-axial system that accommodates the heterogeneity of persons with similar or the same diagnosis. By contributing to the evaluation of outcome risks, this system is of important value in evaluating long-term prognosis.
The axes are as follows:
Axis I: Clinical disorders
Other conditions that may be a focus of clinical attention Axis II: Personality disorders
Mental retardation (intellectual disability) Axis III: General medical conditions
Axis IV: Psychosocial and environmental problems Axis V: Global assessment of functioning
39 2.3.3.3 Classification based on degree of severity
Intellectual disability is classified into five main degrees of severity by both DSM-IV-TR (APA, 2000) and ICD-10 (WHO, 1996). These are mild, moderate, severe, profound, and unspecified.
Mild intellectual disability: An IQ range of 50-69, using properly standardised intelligence tests, indicates mild intellectual disability (WHO, 1996). This is defined as an IQ of 50-55 to approximately 70 by DSM-IV-TR (APA, 2000). Formerly referred to as ‗educable‘, this group constitutes about 85.0% of PWID. Most people functioning at this level acquire language, though with some delay, that is adequate for everyday conversations and clinical interviews. They have minimal impairment in sensorimotor areas and may not be distinguishable from other children until later in life. These individuals can achieve total independence in self-care, though may be slower than expected. During adult life, their level of dependence may be challenged by deficiencies in understanding and use of language. Those functioning at a higher level may cope better with work requiring practical rather than academic skills. They may achieve academic skills up to the sixth grade by their late teens. During adulthood, they usually achieve sufficient social and vocational skills to work or live independently or to be supervised in the community with minimal support. Conversely, they may need supervision or guidance when facing unusual social or economic stress.
According to WHO (1996), they have limited problems in a socio-cultural context as opposed to with academic achievements. However, signs of emotional and social immaturity can still be apparent in response to social responsibilities. Generally, persons with mild intellectual disability do not differ significantly from people of normal intelligence with regards to behavioural, emotional and social difficulties and treatment and support needs. Brain abnormalities are identifiable only in a minority of them. Associated conditions, including autism, other developmental disorders, epilepsy, conduct disorders or physical disability, may be present in varying proportions.
Moderate intellectual disability: The IQ range is 35-49 on ICD-10 and 35-40 to 50-55 on DSM- IV-TR. Previously referred to as ‗trainable‘, this creates an inaccurate impression that they cannot benefit from educational programmes. They constitute about 10.0% of the intellectually
40 disabled population. This group is characterised by discrepancies in profiles of abilities. The levels of language and visuo-spatial development are variable. Development of comprehension and use of language is often slow, and never complete, in this category. Language usage varies from being able to take part in simple conversations to merely being able to communicate basic needs. Some may understand simple instructions and learn manual signs to compensate for their speech disabilities.
They may need lifelong supervision in the area of self-care and motor skills. They can benefit from learning vocational and social skills in a supervised community setting but are unlikely to go beyond second grade in terms of academic achievement. Moreover, they can learn to navigate familiar places independently. Relationships with peers may be hampered during adolescence due to their lack of social skills.
Brain abnormality is common in most moderately intellectually disabled persons. Autism, epilepsy, and neurological and physical disabilities are common, although most of them are mobile. There is the possibility of psychiatric conditions which are often difficult to diagnose due to limited communicative ability. The diagnosing professional may have to rely on information obtained from others who are familiar with the persons.
Severe intellectual disability: The IQ for this group is in the range of 20-34 on ICD-10 and 20-35 to 35-40 on DSM-IV-TR. They constitute 3.0-4.0% of PWID. Broadly speaking, severe intellectual disability is similar to moderate intellectual disability in the clinical picture, and both are characterised by the presence of brain abnormality and associated conditions. However, they function at the lower level of moderate intellectual disability. Most of them have significant limitation of motor skills use, indicating a major deficit in the development of the central nervous system.
They acquire little or no communication skills in childhood, and may only learn to talk during the school-age period. They can also be trained in elementary self-care skills. Basic survival skills, including sight-reading of essential words, may be learned according to their level of cognition. In adulthood, they may learn to perform simple tasks in closely supervised settings.
41 This group can also adapt well to life in the community, group homes or with their families if they do not require any special care.
Profound intellectual disability: Their IQ is under 20 on ICD-10 and below 20 or 25 on DSM-IV- TR. They constitute approximately 1.0-2.0% of people with intellectual disability. There are considerable impairments in sensorimotor functioning during early childhood. Affected individuals are grossly limited in their ability to understand or comply with requests or instructions. They are mostly immobile or severely restricted in mobility, incontinent, and capable of only very rudimentary forms of non-verbal communication. A highly structured environment with constant aid and supervision and an individualised relationship with a caregiver may lead to optimal development. The ability to care for their basic needs and motor skills may also improve if adequate training is provided. Some can perform simple tasks in closely supervised and sheltered settings.
Brain abnormality is associated with most cases. Associated conditions include severe neurological or other physical disabilities, epilepsy, and visual and hearing impairments.
Pervasive and most severe forms of developmental disorders such as atypical autism are common in those who are mobile.
Unspecified intellectual disability: This is characterised by evidence of intellectual disability but lack of information for specific diagnosis. It is common in infants because they are too young for the available tests to yield IQ values. This may also occur when children or adolescents have associated impairments (e.g. deafness, blindness, muteness) or are uncooperative when being tested. Essentially, the younger the person, the more difficult it is to assess the presence of intellectual disability, except with profound impairment.
2.3.3.4 2002 AAIDD classification
The AAIDD defines mental retardation (intellectual disability) as ‗a disability characterised by significant limitations both in intellectual functioning and in adaptive behaviour as expressed in
42 conceptual, social, and practical adaptive skills. The disability originates before age 18‘
(Luckasson et al., 2002).
The definition adopts a multi-dimensional approach by covering both intellectual functioning and adaptive behaviour. Intellectual functioning is measured with an IQ test, and an IQ test result of 70-75 (approximately two standard deviations below the mean) indicates a limitation in intellectual functioning. Adaptive behaviour, which can also be measured with standardised tests, comprises three skill types:
Conceptual skills: language and literacy; money, time and number concepts; and self- direction
Social skills: interpersonal skills, social responsibility, self-esteem, gullibility, naiveté (i.e. wariness), social problem-solving, and the ability to follow rules/obey laws and to avoid being victimised
Practical skills: activities of daily living (personal care), occupational skills, healthcare, travel/transportation, schedules/routines, safety, use of money, and use of the telephone Furthermore, AAIDD stresses that the definition and assessment of intellectual disability must consider the community environment typical of the individual‘s peers and culture. Professionals must also take into account linguistic diversity and cultural differences that influence the way people communicate, move, and behave. Lastly, assessments must assume that limitations in individuals often coexist with strengths, and that a person‘s level of life functioning will improve if appropriate personalised support is provided over a sustained period.
The AAIDD multi-dimensional classification system is based on the following five dimensions (Luckasson et al., 2002):
Dimension I: Intellectual abilities
Dimension II: Adaptive behaviour (conceptual, social, and practical skills) Dimension III: Participation, interactions, and social roles
Dimension IV: Health (physical health, mental health, and aetiology) Dimension V: Context (environments and culture)
43 In conclusion, the AAIDD definition suggests that the majority of affected individuals are expected to improve in their functioning whereas support is needed to maintain a basic level of function or, primarily, to slow potential regression. It also indicates that support planning should be focused on person-centred outcomes.