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DSM-II

In DSM-II, this disorder is called Mental Retardation

Mental retardation refers to subnormal general intellectual functioning which originates during the developmental period and is associated with impairment of either learning and social adjustment or maturation, or both. The diagnostic classification of mental retardation relates to IQ as follows:

  • Borderline mental retardation - IQ 68-85
  • Mild mental retardation - IQ 52-67
  • Moderate mental retardation - IQ 36-51
  • Severe mental retardation - IQ 20-35
  • Profound mental retardation - IQ under 20

These classifications are based on the statistical distribution of levels of intellectual functioning for the population as a whole. The range of intelligence subsumed under each classification corresponds to one standard deviation, making the heuristic assumption that intelligence is normally distributed. It is recognized that the intelligence quotient should not be the only criterion used in making a diagnosis of mental retardation or in evaluating its severity. It should serve only to help in making a clinical judgment of the patient's adaptive behavioral capacity. This judgment should also be based on an evaluation of the patient's developmental history and present functioning, including academic and vocational achievement, motor skills, and social and emotional maturity.

  • Unspecified mental retardation

This classification is reserved for patients whose intellectual functioning has not or cannot be evaluated precisely but which is recognized as clearly subnormal.

DSM-III

In DSM-IV, this disorder is called Mental Retardation

Diagnostic Criteria

A. Significantly subaverage general intellectual functioning: an IQ of 70 or below on an individually administered IQ test (for infants, since available intelligence tests do not yield numerical values, a clinical judgment of significant subaverage intellectual functioning).

B. Concurrent deficits or impairment in adaptive behavior, taking the person's age into consideration.

C. Onset before the age of 18.

Subtypes

There are four subtypes, reflecting the degree of intellectual impairment and designated as Mild, Moderate, Severe, and Profound. IQ levels to be used as guides for distinguishing the four subtypes are given below:

  • Mild: 50-70
  • Moderate: 35-49
  • Severe: 20-34
  • Profound: Below 20

Mild Mental Retardation

Mild Mental Retardation is roughly equivalent to the educational category "educable." This group makes up the largest segment of those with the disorder - about 80%. Individuals with this level of Mental Retardation can develop social and communication skills during the preschool period (ages 0-5), have minimal impairment in sensorimotor areas, and often are not distinguishable from normal children until a later age. By their late teens they can learn academic skills up to approximately the sixth-grade level; and during the adult years, they can usually achieve social and vocational skills adequate for minimum self-support, but may need guidance and assistance when under unusual social or economic stress.

Moderate Mental Retardation

Moderate Mental Retardation is roughly equivalent to the educational category of "trainable." This group makes up 12% of the entire population of individuals with Mental Retardation. Those with this level of Mental Retardation during the preschool period can talk or learn to communicate, but they have only poor awareness of social conventions. They may profit from vocational training and can take care of themselves with moderate supervision. During the school-age period, they can profit from training in social and occupational skills, but are unlikely to progress beyond the second-grade level in academic subjects. They may learn to travel alone in familiar places. During their adult years they may be able to contribute to their own support by performing unskilled or semi-skilled work under close supervision in sheltered workshops. They need supervision and guidance when under mild social or economic stress.

Severe Mental Retardation

This group makes up 7% of individuals with Mental Retardation. During the preschool period there is evidence of poor motor development and minimal speech, and they develop little or no communicative speech. During the school-age period, they may learn to talk and can be trained in elementary hygiene skills. They are generally unable to profit from vocational training. During their adult years they may be able to perform simple work tasks under close supervision.

Profound Mental Retardation

This group constitutes less than 1% of individuals with Mental Retardation. During the preschool period these children display minimal capacity for sensorimotor functioning. A highly structured environment, with constant aid and supervision, is required. During the school-age period, some further motor development may occur and the children may respond to minimal or limited training in self-care. Some speech and further motor development may take place during the adult years, and very limited self-care may be possible, in a highly structured environment with constant aid and supervision.

Unspecified Mental Retardation

This category should be used when there is a strong presumption of Mental Retardation but the individual is untestable by standard intelligence tests. This may be the case when children, adolescents or adults are too impaired or uncooperative to be tested. In the case of infants, since the available tests, such as the Bayley, Cattel, and others, do not yield numerical IQ values, this may be the case when there is a clinical judgment of significant subaverage intellectual functioning. In general, the younger the age, the more difficult it is to make a diagnosis of Mental Retardation, except for those with profound impairment.

This category should not be used when the intellectual level is presumed to be above 70.

Differential Diagnosis

The diagnosis of Mental Retardation should be made whenever present regardless of the presence of another diagnosis.

Specific Developmental Disorders and Pervasive Developmental Disorders

In Specific Developmental Disorders there is a delay or failure of development in a specific area, such as reading or language, but in other areas of development the child is developing normally. In contrast, the child with Mental Retardation shows general delays in development in many areas. In Pervasive Developmental Disorders there are distortions in the timing, rate, and sequence of many basic psychological functions involved in the development of social skills and language. Furthermore, there are severe qualitative abnormalities that are not normal for any stage of development, whereas in Mental Retardation there are generalized delays in development, but the children behave as if they were passing through an ealier normal developmental stage. Mental Retardation may, however, coexist with Specific Developmental Disorders, and frequently coexists with Pervasive Developmental Disorders.

Borderline Intellectual Functioning

Borderline Intellectual Functioning is recorded when there are deficits in adaptive behavior associated with borderline intellectual functioning, which generally is in the IQ range of 71 to 84. Differentiating Mild Mental Retardation from Borderline Intellectual Functioning requires careful consideration of all available information, including psychological test scores.

DSM-IV

In DSM-IV, this disorder is called Mental Retardation

Diagnostic Criteria

A. Significantly subaverage intellectual functioning: an IQ of approximately 70 or below on an individually administered IQ test (for infants, a clinical judgement of significantly subaverage intellectual functioning).

B. Concurrent deficits or impairments in present adaptive functioning (i.e., the person's effectiveness in meeting the standards expected for his or her age by his or her cultural group) in at least two of the following areas: communication, self-care, home living, social/interpersonal skills, use of community, resources, self-direction, functional academic skills, work, leisure, health, and safety.

C. The onset is before age 18 years.

Specify degree of severity reflecting level of intellectual impairment:

  • Mild Mental Retardation: IQ level 50-55 to approximately 70
  • Moderate Mental Retardation: IQ level 35-40 to 50-55
  • Severe Mental Retardation: IQ level 20-25 to 35-40
  • Profound Mental Retardation: IQ level below 20 or 25
  • Mental Retardation, Severity Unspecified: with there is strong presumption of Mental Retardation but the person's intelligence is untestable by standard tests

Degrees of Severity

Four degrees of severity can be specified, reflecting the level of intellectual impairment: Mild, Moderate, Severe, and Profound.

Mild Mental Retardation

Mild Mental Retardation is roughly equivalent to what used to be referred to as the educational category of "educable." This group constitutes the largest segment (about 85%) of those with the disorder. As a group, people with this level of Mental Retardation typically develop social and communication skills during the preschool years (ages 0-5 years), have minimal impairment in sensorimotor areas, and often are not distinguishable from children without Mental Retardation until a later age. By their late teens, they can acquire academic skills up to approximately the sixth-grade level. During their adult years, they usually achieve social and vocational skills adequate for minimum self-support, but may need supervision, guidance, and assistance, especially when under unusual social or economic stress. With appropriate supports, individuals with Mild Mental Retardation can usually live successfully in the community, wither independently or in supervised settings.

Moderate Mental Retardation

Moderate Mental Retardation is roughly equivalent to what used to be referred to as the educational category of "trainable." This outdated terms should not be used because it wrongly implies that people with Moderate Mental Retardation cannot benefit from educational programs. This group constitutes about 10% of the entire population of people with Mental Retardation. Most of the individuals with this level of Mental Retardation acquire communication skills during early childhood years. They profit from vocational training and, with moderate supervision, can attend to their personal care. They can also benefit from training in social and occupational skills but are unlikely to progress beyond the second-grade level in academic subjects. They may learn to travel independently in familiar places. During adolescence, their difficulties in recognizing social conventions may interfere with peer relationships. In their adult years, the majority are able to perform unskilled or semiskilled work under supervision in sheltered workshops or in the general work force. They adapt well to life in the community, usually in supervised settings.

Severe Mental Retardation

The group with Severe Mental Retardation constitutes 3%-4% of individuals with Mental Retardation. During the early childhood years, they acquire little or no communicative speech. During the school-age period, they may learn to talk and can be trained in elementary self-care skills. They profit to only a limited extent from instruction in pre-academic subjects, such as familiarity with the alphabet and simple counting, but can master skills such as learning sight reading of some "survival" words. In their adult years, they may be able to perform simple tasks in closely supervised settings. Most adapt well to life in the community, in group homes or with their families, unless they have an associated handicap that requires specialized nursing or other care.

Profound Mental Retardation

The group with Profound Mental Retardation constitutes approximately 1%-2% of people with Mental Retardation. Most individuals with this diagnosis have an identified neurological condition that accounts for their Mental Retardation. During the early childhood years, they display considerable impairments in sensorimotor functioning. Optimal development may occur in a highly structured environment with constant aid and supervision and an individualized relationship with a caregiver. Motor development and self-care and communication skills may improve if appropriate training is provided. Some can perform simple tasks in closely supervised and sheltered settings.

Mental Retardation, Severity Unspecified

The diagnosis of Mental Retardation, Severity Unspecified, should be used when there is a strong presumption of Mental Retardation but the person cannot be successfully tested by standard intelligence tests. This may be the case when children, adolescents, or adults are too impaired or uncooperative to be tested or, with infants, when there is a clinical judgement of significantly subaverage intellectual functioning, but the available tests (e.g., the Bayley Scales of Infant Development, Cattell Infant Intelligence Scales, and others) do not yield IQ values. In general, the younger the age, the more difficult it is to assess for the presence of Mental Retardation except in those with profound impairment.

Recording Procedures

If Mental Retardation is associated with another mental disorder (e.g., Autistic Disorder), the additional mental disorder is recorded. If Mental Retardation is associated with a general medical condition (e.g., Down's syndrome), the general medical condition is recorded.

Differential Diagnosis

The diagnostic criteria for Mental Retardation do not include an exclusion criterion; therefore, the diagnosis should be made whenever the diagnostic criteria are met, regardless of and in addition to the presence of another disorder.

Learning and Communication Disorders

In Learning Disorders and Communication Disorders (unassociated with Mental Retardation), the development in a specific area (e.g., reading, expressive language) is impaired but there is no generalized impairment in intellectual development and adaptive functioning. A Learning Disorder or Communication Disorder can be diagnosed in an individual with Mental Retardation if the specific deficit is out of proportion to the severity of the Mental Retardation.

Pervasive Developmental Disorders

In Pervasive Developmental Disorders, there is qualitative impairment in the development of reciprocal social interaction and in the development of verbal and nonverbal social communication skills. Mental Retardation often accompanies Pervasive Developmental Disorder (75%-80% of individuals with a Pervasive Developmental Disorder also have Mental Retardation).

Dementia

Some cases of Mental Retardation have their onset after a period of normal functioning and may qualify for the additional diagnosis of dementia. A diagnosis of dementia requires that the memory impairment and other cognitive deficits represent a significant decline from a previously higher level of functioning. Because it may be difficult to determine the previous level of functioning in very young children, the diagnosis of dementia may not be appropriate until the child is between ages 4 and 6 years. In general, for individuals under age 18 years, the diagnosis of dementia is made only when the condition is not characterized satisfactory by the diagnosis of Mental Retardation alone.

Borderline Intellectual Functioning

Borderline Intellectual Functioning describes an IQ range that is higher than that for Mental Retardation (generally 71-84). An IQ score may involve a measurement error of approximately 5 points, depending on the testing instrument. Thus, it is possible to diagnose Mental Retardation in individuals with IQ scores between 71 and 75 if they have significant deficits in adaptive behavior that meet the criteria for Mental Retardation. Differentiating Mild Mental Retardation from Borderline Intellectual Functioning requires careful consideration of all available information.

DSM-5

Diagnostic Criteria

Intellectual disability (intellectual developmental disorder) is a disorder with onset during the developmental period that includes both intellectual and adaptive functioning deficits in conceptual, social, and practical domains. The following three criteria must be met:

A. Deficits in intellectual functions, such as reasoning, problem solving, planning, abstract thinking, judgement, academic learning, and learning from experience, confirmed by both clinical assessment and individualized, standardized intelligence testing.

B. Deficits in adaptive functioning that result in failure to meet developmental and sociocultural standards for personal independence and social responsibility. Without ongoing support, the adaptive deficits limit functioning in one or more activities of daily life, such as communication, social participation, and independent living, across multiple environments, such as home, school, work, and community.

C. Onset of intellectual and adaptive deficits during the developmental period.

Specify current severity:

  • Mild
  • Moderate
  • Severe
  • Profound

Specifiers

The various levels of severity are defined on the basis of adaptive functioning, and not IQ scores, because it is adaptive functioning that determines the level of supports required. Moreover, IQ measures are less valid in the lower end of the IQ range.

Mild

Conceptual domain: For preschool children, there may be no obvious conceptual differences. For school-age children and adults, there are difficulties in learning academic skills involving reading, writing, arithmetic, time, or money, with support needed in one or more areas to meet age-related expectations. In adults, abstract thinking, executive function (i.e., planning, strategizing, priority setting, and cognitive flexibility), and short-term memory, as well as functional use of academic skills (e.g., reading, money management), are impaired. There is a somewhat concrete approach to problems and solutions compared with age-mates.

Social domain: Compared with typically developing age-mates, the individual is immature in social interactions. For example, there may be difficulty in accurately perceiving peers' social cues. Communication, conversation, and language are more concrete or immature than expected for age. There may be difficulties regulating emotion and behavior in age-appropriate fashion; these difficultues are noticed by peers in social situations. There is limited understanding of risk in social situations; social judgement is immature for age, and the person is at risk of being manipulated by others (gullibility).

Practical domain: The individual may function age-appropriately in personal care. Individuals need some support with complex daily living tasks in comparison to peers. In adulthood, supports typically involve grocery shopping, transportation, home and child-care organizing, nutritious food preparation, and banking and money management. Recreational skills resemble those of age-mates, although judgement related to well-being and organization around recreation requires support. In adulthood, competitive employment is often seen in jobs that do not emphasize conceptual skills. Individuals generally need support to make health care decisions and legal decisions, and to learn to perform a skilled vocation competently. Support is typically needed to raise a family.

Moderate

Conceptual domain: All through development, the individual's conceptual skills lag markedly behind those of peers. For preschoolers, language and pre-academic skills develop slowly. For school-age children, progress in reading, writing, mathematics, and understanding of time and money occurs slowly across the school years and is markedly limited compared with that of peers. For adults, academic skill development is typically at an elementary level, and support is required for all use of academic skills in work and personal life. Ongoing assistance on a daily basis is needed to complete conceptual tasks of day-to-day life, and others may take over these responsibilities fully for the individual.

Social domain: The individual shows marked differences from peers in social and communicative behavior across development. Spoken language is typically a primary tool for social communication but is much less complex than that of peers. Capacity for relationships is evident in ties to family and friends, and the individual may have successful friendships across life and sometimes romantic relations in adulthood. However, individuals may not perceive or interpret social cues accurately. Social judgement and decision-making abilities are limited, and caretakers must assist the person with life decisions. Friendships with typically developing peers are often affected by communication or social limitations. Significant social and communicative support is needed in work settings for success.

Practical domain: The individual can care for personal needs involving eating, dressing, elimination, and hygiene as an adult, although and extended period of teaching and time is needed for the individual to become independent in these areas, and reminders may be needed. Similarly, participation in all household tasks can be achieved by adulthood, although an extended period of teaching is needed, and ongoing supports will typically occur for adult-level performance. Independent employment in jobs that require limited conceptual and communication skills can be achieved, but considerable support from co-workers, supervisors, and others is needed to manage social expectations, job complexities, and ancillary responsibilities such as scheduling, transportations, health benefits, and money management. A variety of recreational skills can be developed. These typically require additional supports and learning opportunities over an extended period of time. Maladaptive behavior is present in a significant minority and causes social problems.

Severe

Conceptual domain: Attainment of conceptual skills is limited. The individual generally has little understanding of written language or of concepts involving numbers, quantity, time, and money. Caretakers provide extensive supports for problem solving throughout life.

Social domain: Spoken language is quite limited in terms of vocabulary and grammar. Speech may be single words or phrases and may be supplemented through augmentative means. Speech and communication are focused on the here and now within everyday events. Language is used for social communication more than for explication. Individuals understand simple speech and gestural communication. Relationships with family members and familiar others are a source of pleasure and help.

Practical domain: The individual requires support for all activities of daily living, including meals, dressing, bathing, and elimination. The individual requires supervision at all times. The individual cannot make responsible decisions regarding well-being of self or others. In adulthood, participation in tasks at home, recreation, and word requires ongoing support and assistance. Skill acquisition in all domains involves long-term teaching and ongoing support. Maladaptive behavior, including self-injury, is present in a significant minority.

Profound

Conceptual domain: Conceptual skills generally involve the physical world rather than symbolic processes. The individual may use objects in goal-directed fashion for self-care, work, and recreation. Certain visuospatial skills, such as matching and sorting based on physical characteristics, may be acquired. However, co-occurring motor and sensory impairments may prevent functional use of objects.

Social domain: The individual has very limited understanding of symbolic communication in speech or gesture. He or she may understand some simple instructions or gestures. The individual expresses his or her own desires and emotions largely through nonverbal, nonsymbolic communication. The individual enjoys relationships with well-known family members, caretakers, and familiar others, and initiates and responds to social interactions through gestural and emotional cues. Co-occurring sensory and physical impairments may prevent many social activities.

Practical domain: The individual is dependent on others for all aspects of daily physical care, health, and safety, although he or she may be able to participate in some of these activities as well. Individuals without severe physical impairments may assist with some daily work tasks at home, like carrying dishes to the table. Simple actions with objects may be the basis of participation in some vocational activities with high levels of ongoing support. Recreational activities may involve, for example, enjoyment in listening to music, watching movies, going out for walks, or participating in water activities, all with the support of others. Co-occurring physical and sensory impairments are frequent barriers to participation (beyond watching) in home, recreational, and vocational activities. Maladaptive behavior is present in a significant minority.

Differential Diagnosis

The diagnosis of intellectual disability should be made whenever Criteria A, B, and C are met. A diagnosis of intellectual disability should not be assumed because of a particular genetic or medical condition. A genetic syndrome linked to intellectual disability should be noted as a concurrent diagnosis with the intellectual disability.

Major and mild neurocognitive disorders

Intellectual disability is categorized as a neurodevelopmental disorder and is distinct from the neurocognitive disorders, which are characterized by a loss of cognitive functioning. Major neurocognitve disorder may co-occur with intellectual disability (e.g., an individual with Down syndrome who develops Alzheimer's disease, or an individual with intellectual disability who loses further cognitive capacity following a head injury). In such cases, the diagnoses of intellectual disability and neurocognitive disorder may both be given.

Communication disorders and specific learning disorder

These neurodevelopmental disorders are specific to the communication and learning domains and do not show deficits in intellectual and adaptive behavior. They may co-occur with intellectual disability. Both diagnoses are made if full criteria are met for intellectual disability and a communication disorder or specific learning disorder.

Autism spectrum disorder

Intellectual disability is common among individuals with autism spectrum disorder. Assessment of intellectual ability may be complicated by social-communication and behavior deficits inherent to autism spectrum disorder, which may interfere with understanding and complying with test procedures. Appropriate assessment of intellectual functioning in autism spectrum disorder is essential, with reassessment across the developmental period, because IQ scores in autism spectrum disorder may be unstable, particularly in early childhood.