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Intellectual Disability

Practice Essentials

Intellectual disability (ID), is a descriptive term for subaverage intelligence and impaired adaptive functioning arising in the developmental period (< 18 years).

Signs and symptoms

Patients with ID and developmental delays may demonstrate the following:

Language delay: One of the first signs of ID may be language delays, including delays in expressive language (speech) and receptive language (understanding)

Fine motor/adaptive delay: Significant delays in activities such as self-feeding, toileting, and dressing are typically reported in children with ID

Cognitive delay: Difficulties with memory, problem-solving, and logical reasoning

Social delays: Lack of interest in age-appropriate toys and delays in imaginative play and reciprocal play with age-matched peers

Gross motor developmental delays: Infrequently accompany the cognitive, language, and fine motor/adaptive delays associated with ID unless the underlying condition results in both ID and cerebral palsy.

Behavioral disturbances: Infants and toddlers may be more likely to have difficult temperaments, hyperactivity, disordered sleep, and colic; associated behaviors may include aggression, self-injury, defiance, inattention, hyperactivity, sleep disturbances, and stereotypic behaviors.

Neurologic and physical abnormalities: Prevalence of ID is increased among children with seizure disorders, microcephaly, macrocephaly, history of intrauterine or postnatal growth retardation, prematurity, and congenital anomalies

Evaluation of patients for ID can include the following examinations:

Head circumference: Microcephaly correlates highly with cognitive deficits; macrocephaly may indicate hydrocephalus, is associated with some inborn errors of metabolism, and may be seen early on in some children later diagnosed with autism

Height: Short stature may suggest a genetic disorder, fetal alcohol syndrome, or hypothyroidism; tall stature may suggest fragile X syndrome (FraX), Soto syndrome, or some other overgrowth syndrome associated with MR/ID

Neurologic: This examination should include assessments of head growth (for microcephaly/macrocephaly), muscle tone (for hypotonia or spasticity), strength and coordination, deep tendon reflexes, persistent primitive reflexes, ataxia, and other abnormal movements, such as dystonia or athetosis.

Sensory: Children with disabilities and ID are more likely than other children to have visual impairment and hearing deficits

Skin: Findings can include hyperpigmented and hypopigmented macules, such as café-au-lait macules (associated with neurofibromatosis type 1), as well as ash-leaf spots (associated with tuberous sclerosis), fibromas, and irregular pigmentation patterns

Extremities: Although ID with multiple congenital anomalies and major malformations accounts for only 5-10% of all cases, most of these affected individuals have 3-4 minor anomalies, especially involving the face and digits

See Clinical Presentation for more detail.


Laboratory studies

Array-based comparative genetic hybridization (CGH), or microarray

High-resolution karyotype

Fragile X testing

FISH probes

Imaging studies

Brain magnetic resonance imaging (MRI): Should be conducted in any child with global developmental delays or ID

Head computed tomography (CT) scanning: Preferred imaging study for calcifications that may be identified with TORCH infections (ie, toxoplasmosis, other infections, rubella, cytomegalovirus [CMV], herpes simplex) or when tuberous sclerosis is suspected or craniosynostosis is a concern

Skeletal films: Assist with phenotypic description, syndrome characterization, and assessment of growth

Additional tests

Detailed assessment by a licensed professional is necessary to confirm the diagnosis of ID. Some of the most commonly used tests in children include the following:

Bayley Scales of Infant Development

Stanford-Binet Intelligence Scale

Wechsler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R)

Wechsler Intelligence Scale for Children–IV (WISC-IV)

Vineland Adaptive Behavior Scales-II

See Workup for more detail.


The mainstay of ID treatment is the development of a comprehensive management plan for the condition. The complex habilitation plan for the individual requires input from care providers from multiple disciplines, including special educators, language therapists, behavioral therapists, occupational therapists, and community services that provide social support and respite care for families affected by ID.

Neuropathic pain due to dysautonomia or motor spasms may create chronic disturbances. Treatment should be prompt and include the following:

Nonsteroidal anti-inflammatory drugs (NSAIDs) or acetaminophen for mild pain

Tramadol or equivalent for moderate pain

Opioids for severe pain as indicated

Management of sources of pain

No specific pharmacologic treatment is available for cognitive impairment in the developing child or adult with ID.
Medications, when prescribed, are targeted to specific comorbid psychiatric disease or behavioral disturbances.

The psychostimulant class of drugs is commonly prescribed in individuals with ID, because of the diagnosis of attention deficit with or without hyperactivity disorder (ADHD/ADD) in 6-80% of these patients. However, few studies on stimulants in people with MR/ID are available. The studies that do exist indicate that benefits vary, and significant adverse events, such as severe social withdrawal, increased crying, drowsiness, and irritability, have been noted, especially at higher doses of methylphenidate (0.6 mg/kg).

The neuroleptic drugs are the most frequently prescribed agents for targeting behaviors such as aggression, self-injury, and hyperactivity in people with MR/ID. These indications are generally off-label for ID and caution is advised.

See Treatment and Medication for more detail.

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