Autism or Something Else? Knowing the Difference
Many young children referred for possible autism turn out to have a language delay, an intellectual disability, a hearing problem, or a social communication disorder instead — and some have autism alongside another condition. This clinical reference walks through the DSM-5 criteria for autism spectrum disorder, the social-emotional milestones that anchor a developmental history, validated screening tools, and the key differential diagnoses.
A case to consider
Two-year-old Caleb runs in behind his mother and doesn't respond when you greet him by name. His mother says his speech is behind and she's worried about autism. He's attached to her and his older brother but won't play with anyone else. He has about 30 single words but isn't combining two words yet. He loves dinosaurs and trains — and that's all he wants to play with at home. He also toe-walks.
Autism, or something else? The features overlap with several conditions. The sections below lay out how to tell them apart — starting with what specifically defines autism.
What Makes Autism Different
Speech/language delay and broader developmental delay are common to many conditions. What distinguishes autism spectrum disorder (ASD) is the combination of impairments in social communication with restricted, repetitive, or unusual behaviors. A child can have a language or developmental delay without having either of those autism-specific domains.
DSM-5 Diagnostic Criteria
DSM-5 consolidated the older DSM-IV diagnoses — autistic disorder, Asperger's disorder, and pervasive developmental disorder — into the single umbrella of autism spectrum disorder, described along a severity spectrum rather than as separate categories.
A diagnosis of ASD requires deficits across two domains:
1. Persistent deficits in social communication and interaction
- Social-emotional reciprocity — e.g., unable to sustain back-and-forth conversation.
- Nonverbal communication — poor eye contact; reduced use of gesture and facial expression.
- Developing and maintaining relationships — absence of friends, no imaginative play, or inappropriate play.
2. Restricted, repetitive patterns of behavior, interests, or activities
- Stereotyped or repetitive motor movements, use of objects, or speech.
- Insistence on sameness; ritualized routines; rigid verbal or nonverbal patterns.
- Highly restricted, fixated interests that are abnormal in focus or intensity.
- Sensory hyper- or hypo-reactivity, or unusual interest in sensory aspects of the environment.
Additional requirements
To make the diagnosis, symptoms must also be present in early development, cause significant impairment in social, occupational, or everyday functioning, and not be better explained by intellectual disability or global developmental delay — though ASD can co-exist with either.
Severity Levels
DSM-5 grades ASD by the level of support required across both core domains.
| Level | Descriptor | Support needed |
|---|---|---|
| Level 1 | Mild | Requiring support |
| Level 2 | Moderate | Requiring substantial support |
| Level 3 | Severe | Requiring very substantial support |
Typical Social-Emotional Development
Knowing the typical trajectory makes deviations easier to spot. These social-emotional milestones anchor a developmental history.
| Age | Social-emotional milestone |
|---|---|
| 6 mo | Jointly attends to actions and objects of interest to caregivers |
| 8 mo | Engages in gaze monitoring (follows caregiver's gaze with own eyes) |
| 9 mo | Looks preferentially when name is called; follows a point; enjoys interactive games (peek-a-boo) |
| 12 mo | Protoimperative pointing (points to get a desired object); lets adults know help is needed |
| 14 mo | Proto-declarative pointing (points at an object to share interest) |
| 15 mo | Shows empathy (looks sad when someone cries); hugs an adult in reciprocation |
| 18 mo | Engages in pretend play (feeds a doll, talks on a toy phone) |
| 24 mo | Engages in parallel play; begins to have thoughts about feelings ("Mommy, are you sad?") |
| 30 mo | Shows imaginative and symbolic play (turns an object into something new) |
| 36 mo | More elaborate imaginative play; uses stories to describe what someone else is thinking |
Red-Flag Symptoms for Possible ASD
- No babbling, pointing, or other gesture by 12 months.
- No single words by 16 months.
- No spontaneous two-word phrases (not echolalia) by 24 months.
- Loss of language or social skills at any age.
Screening & Surveillance
Screen development at every well-child visit, and use a standardized developmental tool at the 9-, 18-, and 24- or 30-month visits. General developmental screens include Ages & Stages (4–60 months), the Denver Developmental Profile, and PEDS (Parents' Evaluation of Developmental Status).
Add an autism-specific screen at 18, 24, and/or 30 months using the M-CHAT-R (Modified Checklist for Autism in Toddlers, Revised).
About the M-CHAT-R
- Validated for ages 16–30 months.
- Sensitivity ~94%, specificity ~83%.
- 20 yes/no questions completed by the parent; takes about 5–10 minutes.
- Simple scoring, with a structured follow-up interview for medium-risk scores.
Differential Diagnosis
ASD vs. intellectual disability
Autism spectrum disorder
- Lack of social interaction.
- Lack of gestures to support communication.
- Repetitive, stereotyped movements that impede function.
Intellectual disability
- Social interaction present, though not at age level.
- Uses gestures to support communication.
- Repetitive/stereotyped movements mainly in severe-to-profound ID.
The discriminating feature is social reciprocity and gesture use: a child with isolated intellectual disability still reaches toward others and uses gesture to communicate, whereas the child with ASD characteristically does not.
Social (pragmatic) communication disorder
This diagnosis describes persistent difficulty with the social use of verbal and nonverbal communication, without the restricted/repetitive behaviors that define ASD. It is manifested by all of the following:
- Deficits in using communication for social purposes.
- Impaired ability to adapt communication to the context or the listener's needs; difficulty following the rules of conversation and storytelling.
- Difficulty understanding what is not explicitly stated.
- Functional limitations in communication, social participation, relationships, or academic/occupational performance.
Onset is in the early developmental period, and the symptoms are not better explained by another condition. Because the restricted/repetitive domain is absent, this is a key "something else" to weigh against ASD.
Co-occurring Conditions
Autism frequently travels with medical and psychiatric comorbidities. Recognizing them is part of complete care — and sometimes the comorbidity, not the autism, is what's driving a new concern.
Medical
- Sleep disturbance — 52–73%
- GERD / constipation — 8–59%
- Food selectivity — 30–90%
- Seizure disorder — 5–49%
- Language deficits — 50–63%
- Hypotonia — ~50%
- Motor delay — 9–19%
- Tics — 8–10%
Psychiatric / behavioral
- Intellectual disability — 40–80%
- Sensory issues: tactile 80–90%, auditory 5–47%
- Anxiety — 43–84%
- Attention problems / hyperactivity — ~59%
- OCD-type behaviors — ~37%
- Self-injurious behavior — ~34%
- Disruptive / aggressive behavior — 8–32%
- Depression — 2–30%; ODD — ~7%
Prevalence ranges as cited in the source presentation; psychiatric figures drawn in part from Levy et al., Lancet, 2009.
Regression
Up to 30% of children with ASD experience regression, which may be gradual or sudden — stopping talking, dropping gestural communication, or losing social skills.
Practice Change
- Perform formal developmental screening at every well-child check — and any time a parent raises a concern.
- Screen specifically for ASD at 18, 24, and 30 months.
- Always obtain a formal hearing evaluation for any child with speech/language delay.
Resources & References
Screening tools & toolkits
- M-CHAT-R/F (screen, scoring, and follow-up): mchatscreen.com/mchat-rf/scoring
- CDC "Learn the Signs. Act Early." milestones: cdc.gov/ncbddd/actearly
- CDC Autism Case Training modules: cdc.gov · autism case training
- Autism Speaks toolkits (First 100 Days, Toilet Training, Constipation): autismspeaks.org/tool-kits