DSM-5 Diagnostic Criteria for Intellectual Disability
Intellectual Disability (Intellectual Developmental Disorder) is diagnosed when three criteria are met:
Criterion A: Deficits in Intellectual Functioning
Requirements:
- Deficits in intellectual functions confirmed by both:
- Clinical assessment (professional judgment)
- Standardized intelligence testing (IQ tests)
Areas Affected:
- Reasoning: Logical thinking, drawing conclusions
- Problem-solving: Finding solutions to challenges
- Planning: Organizing and preparing for future tasks
- Abstract thinking: Understanding concepts, metaphors, symbolism
- Judgment: Making sound decisions
- Academic learning: Acquiring knowledge from instruction
- Learning from experience: Applying past lessons to new situations
Assessment Methods:
- IQ Tests: Wechsler Intelligence Scales (WISC, WAIS), Stanford-Binet
- Clinical Observation: Professional evaluation of cognitive abilities
- Expected Score: Generally IQ approximately 70 or below (2 standard deviations below mean)
- Note: DSM-5 emphasizes clinical judgment over strict IQ cutoffs
Criterion B: Deficits in Adaptive Functioning
Definition: Failure to meet developmental and sociocultural standards for personal independence and social responsibility.
Must Affect at Least One of Three Domains:
1. Conceptual Domain:
- Language: Understanding and using spoken/written communication
- Reading and writing: Literacy skills
- Math: Numeracy and money concepts
- Reasoning: Logical thinking and problem-solving
- Memory: Retaining and recalling information
- Knowledge: General information and learning
2. Social Domain:
- Interpersonal communication: Conversing with others
- Social judgment: Understanding social cues and norms
- Empathy: Understanding others’ feelings
- Friendship skills: Making and maintaining relationships
- Following rules: Understanding and complying with social expectations
- Avoiding victimization: Recognizing and avoiding manipulation
3. Practical Domain:
- Self-care: Personal hygiene, dressing, eating
- Job responsibilities: Performing work tasks
- Money management: Handling finances
- Recreation: Organizing leisure activities
- School/work organization: Managing tasks and schedules
- Transportation: Getting around independently
- Healthcare: Managing medical needs
- Safety: Keeping oneself safe from harm
Assessment Methods:
- Adaptive Behavior Scales: Vineland Adaptive Behavior Scales, AAMR Adaptive Behavior Scale
- Clinical interview: With individual and caregivers
- Observation: In natural settings
- Comparison: To age and culturally appropriate expectations
Criterion C: Onset During Developmental Period
Requirements:
- Intellectual and adaptive deficits must have onset during the developmental period
- Developmental period: Typically defined as before age 18
- Symptoms must be present since childhood/adolescence, not acquired later in life
Why This Matters:
- Distinguishes ID from acquired conditions (traumatic brain injury in adulthood, dementia)
- Emphasizes neurodevelopmental nature
- Affects developmental trajectory from early on
Specifying Severity
Based on Adaptive Functioning (not IQ alone):
Mild Intellectual Disability (IQ 50-70)
Conceptual:
- Can learn academic skills at elementary to early middle school level (6th-8th grade)
- Concrete thinking; difficulty with abstract concepts
- Can handle money, tell time with support
- May need help with complex tasks
Social:
- Social judgment and communication immature compared to peers
- May have difficulty perceiving social cues accurately
- Can maintain friendships with support
- May be manipulated by others
Practical:
- Can function independently in self-care (eating, dressing, hygiene)
- Needs support for complex daily living (grocery shopping, meal planning)
- Can work in jobs not emphasizing conceptual skills
- May need help with healthcare, legal, financial decisions
- Can live independently with support
Moderate Intellectual Disability (IQ 35-49)
Conceptual:
- Academic skills typically at early elementary level
- Language and literacy skills limited
- Understands concrete concepts but not abstract
- May learn functional academic skills (sight words, basic math)
Social:
- Noticeable differences from peers in social and communicative behavior
- Language simpler, less developed
- Capable of relationships but needs support
- Limited social judgment
Practical:
- Requires ongoing support for daily living tasks
- Can participate in self-care with reminders and assistance
- Can learn simple work skills but needs close supervision
- Requires support for all major life decisions
- Typically lives with family or in supported setting
Severe Intellectual Disability (IQ 20-34)
Conceptual:
- Little understanding of written language or number concepts
- Caregivers provide extensive support for problem-solving
- Can learn some daily living skills through long-term teaching
Social:
- Limited spoken language (few words to simple phrases)
- Understands simple speech and gestures
- Relationships mainly with family and caregivers
- Can participate in simple activities with support
Practical:
- Requires support for all activities of daily living
- May participate in simple tasks under close supervision
- Cannot make responsible decisions
- Requires supervised living setting
- May have co-occurring physical/neurological conditions
Profound Intellectual Disability (IQ <20)
Conceptual:
- Limited understanding of symbolic communication
- May understand some simple gestures or instructions
- Uses non-symbolic communication (objects, pictures)
Social:
- Very limited communication; mainly nonverbal
- Responds to direct physical and emotional cues
- Enjoys relationships with familiar caregivers
- Can participate in simple shared activities
Practical:
- Dependent on others for all aspects of care
- May participate minimally in self-care with support
- Often has co-occurring sensory and physical impairments
- Requires 24-hour care and supervision
Additional Diagnostic Considerations
Differential Diagnosis
Must Rule Out:
- Specific Learning Disorder: Normal IQ with specific academic deficits
- Communication Disorders: Language problems without broad intellectual impairment
- Autism Spectrum Disorder: May have normal IQ despite social deficits
- Borderline Intellectual Functioning: IQ 71-84 (not a disorder but may need support)
- Dementia: Acquired decline in functioning (not developmental)
Comorbidity Considerations
Commonly Co-occurs With:
- Cerebral palsy
- Epilepsy
- ADHD
- Depressive and anxiety disorders
- Autism spectrum disorder
- Genetic syndromes (Down syndrome, Fragile X)
Cultural and Environmental Factors
Important Considerations:
- Assessment must be culturally appropriate
- Language barriers should not be mistaken for intellectual disability
- Consider educational opportunities and cultural expectations
- Use culturally normed tests
- Consider socioeconomic factors affecting adaptive behavior
Assessment Process
Comprehensive Evaluation Includes:
1. Cognitive Assessment:
- Standardized IQ testing by qualified psychologist
- Multiple measures preferred
- Consider test limitations and measurement error
2. Adaptive Behavior Assessment:
- Structured interviews with caregivers
- Adaptive behavior rating scales
- Direct observation in natural settings
- Review of developmental history
3. Medical Evaluation:
- Physical examination
- Neurological assessment
- Genetic testing if indicated
- Rule out medical causes
4. Developmental History:
- Pregnancy and birth complications
- Developmental milestones
- Family history
- Educational history
5. Educational/Functional Assessment:
- School performance records
- Current functional abilities
- Support needs assessment
Key Diagnostic Points for Exams
- Three criteria must all be met: Intellectual deficits (A), Adaptive deficits (B), Developmental onset (C)
- Both clinical judgment and testing required for intellectual functioning
- Adaptive functioning is central to severity determination (not just IQ)
- Three adaptive domains: Conceptual, Social, Practical
- Onset before age 18 distinguishes from acquired conditions
- Severity levels: Mild, Moderate, Severe, Profound (based on adaptive functioning)
- IQ scores are guidelines, not absolute cutoffs
- Must significantly limit functioning in everyday life
- Cultural factors must be considered in assessment
- Comprehensive evaluation required: Can’t diagnose on IQ alone