Section E - Mental retardation
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Mental retardation is a permanent condition characterized by subaverage intelligence, which causes limitations in learning and adaptive functioning. Individuals with mental retardation may be able to live independently in the community and obtain various levels of employment, depending on the level of severity; as severity increases, the need for training and support may be required to complete even simple, daily tasks. This section describes the health states of individuals living with mild, moderate, or severe mental retardation.
Mental retardation occurs in all races and cultures, although there is a higher prevalence overall among males than females. Approximately 1-3% of the population are affected;7,121,122 of all cases, the majority (about 85%)7 are classified as having mild severity;122 approximately 10% and 4% of cases have moderate and severe mental retardation, respectively.7 The time of onset typically depends on the cause of the mental retardation. In general, mental retardation is caused by any condition or event that impairs the development of the brain before birth (prenatal), during birth (perinatal), or in childhood (postnatal). Specifically, potential causes include, but are not restricted to, chromosomal deficits (Down syndrome), inherited disorders (Fragile X syndrome, hypothyroidism), errors of metabolism, brain injury or infection (insufficient oxygen during birth, meningitis), prematurity or low birth weight, fetal malnutrition, drug or alcohol misuse during pregnancy (fetal alcohol syndrome), maternal infections (rubella or hypertension), and severe emotional neglect or abuse (including under-stimulation of the infant/child). Unfortunately, in many cases, no specific cause can be identified,7,121 although the likelihood of identifying the particular cause increases with severity of mental retardation.
According to DSM-IV criteria,7 an individual is diagnosed with mental retardation if they have significantly below average intellectual functioning, as defined by an intelligence quotient (IQ; measured using a standardized, individually administer/red intelligence test) at or below 70. In addition, limitations in adaptive functioning (i.e., effective coping of common life demands) are present in at least two of the following skill areas: communication, home living, self-care, self-direction, use of community resources, functional academic skills, social/interpersonal skills, work, leisure, health, and safety. Finally, onset must occur before age 18 years. The DSM-IV classifies mental retardation into four stages based on severity: mild (IQ score of 50-55 to approximately 70), moderate (IQ score of 30-35 to 50-55), severe (IQ score of 20-25 to 35-40), and profound (IQ score of less than 20-25). (The ICD10 has more specific IQ cut-offs; see the health state descriptions for each stage below.) The health state of an individual with profound mental retardation will not be described in this chapter because it accounts for only 1% of all individuals with mental retardation.7
Mental retardation is often suspected when the affected individual fails to meet age-appropriate developmental milestones. In infancy, abnormal development may be apparent by floppy or spastic muscle tone, lack of visual or auditory response, and/or inadequate sucking response.123 Eventually, motor delays in sitting or walking and language and behavioural abnormalities may be evident, but often are not identified until the preschool period. In more severe cases, the symptoms tend to be more obvious, and appear at a younger age. In particular, some individuals may have noticeable physical or neurological abnormalities that may be suggestive of mental retardation, such as unusual facial features, a head that is too small or large, deformities of the hands or feet, and seizures.121
Mental retardation is a permanent condition, however the majority of individuals with mental retardation can receive comprehensive, individualized programs that are aimed at teaching the adaptive skills necessary to increase their level of independence: reading, writing, and basic math, taking care of personal needs (i.e., dressing, bathing), communicating with others, home living (i.e., cooking, cleaning the house), social skills (i.e., manners, playing games), and health and safety. Social programs are also important for the individual with mental retardation to gain self-esteem. In early adulthood, treatment is also directed at learning vocational skills to support employment; involvement in the workforce improves adaptive skills and the success of community living.124 Emotional support for the family is also an integral part of treatment.
Mental retardation – mild
ICD-9 code: 317 ICD-10 – Mild mental retardation F70
An individual is diagnosed with mild mental retardation if they have an IQ score of 50-69,6 and the majority of cases fall within this category. Individuals with mild mental retardation typically develop social and communication skills adequate for self support, but may need assistance during times of unusual stress. Academic skills can be acquired up to the 6th grade level. Given appropriate supports, individuals with mild mental retardation can usually live successfully in the community, either in independent or supervised settings, and 80% are employed (in mainly unskilled or semiskilled jobs).123
Mental retardation – moderate
ICD-9 code: 318.0 ICD-10 – Moderate mental retardation F71
An individual is diagnosed with moderate mental retardation if they have an IQ score of 35-49.6 About 10% of individuals with mental retardation fall within this category.7 Individuals with moderate mental retardation can generally acquire adequate communication skills and benefit from social and occupational skills training, but their academic level does not usually progress beyond the 2nd grade level. They are slow in learning to speak and have fair motor coordination. The majority of individuals are able to manage unskilled or semiskilled work in sheltered conditions with supervision and guidance. They typically live in supervised settings and are able to attend to their personal needs and care under supervision.
Mental retardation – severe
ICD-9 code: 318.1 ICD-10 – Severe mental retardation F72
An individual has severe mental retardation if they have an IQ score of 20-34.6 Approximately 3-4% of all individuals with mental retardation fall within this category.7 Individuals with severe mental retardation may learn to talk and communicate although they have only limited speech skills and vocabulary. The individual can contribute to simple and self-care tasks under close supervision. Motor coordination is poor. Most live in group homes or with their families; however, the likelihood of neurological, neuromuscular, visual, auditory, and cardiovascular conditions in severe mental retardation may require specialized nursing or other care. Self-injurious behaviour, including head-banging, biting, and scratching is not uncommon in children with severe mental retardation.