Many conditions, described as differential diagnosis, present with symptoms like autism. Some of these conditions may also coexist with autism.
Whenever a child is diagnosed with autism some questions must be asked:
- “Is it really ASD or could it be some other condition with symptoms like autism?” and
- “does the child have another condition coexisting with ASD?”
It is recommended[i] that we consider the following conditions for differential diagnosis and undertake specific assessment and/or obtain expert advice to exclude them:
- Neurodevelopmental disorders:
- language delay or disorder
- intellectual disability or global developmental delay
- developmental coordination disorder (DCD).
- Mental and behavioural disorders:
- attention deficit hyperactivity disorder (ADHD)
- mood disorder e.g. depression
- anxiety disorder
- attachment disorders
- oppositional defiant disorder (ODD)
- conduct disorder
- obsessive compulsive disorder (OCD)
- psychosis.
- Conditions in which there is developmental regression:
- Rett syndrome
- epileptic encephalopathy.
- Other conditions:
- severe hearing impairment
- severe visual impairment
- maltreatment
- selective mutism.
Language impairment (LI)
| Presenting features that make it look like ASD | Features that are different from ASD |
| Understanding and use of language is affected | L I children often use non-verbal communication to compensate |
| Play is often immature or delayed | Use of language in ASD remains poor or odd compared to the expressive language ability |
| Social communication is often affected when the language is poor | LI children have more difficulty in speaking than understanding; in ASD the understanding is more affected. |
| Making friends is difficult | Delayed echolalia, rigid repetitive behaviours and over focussed interests are present in ASD and not in LI. |
Intellectual disability (ID)/global developmental impairment
| Presenting features that make it look like ASD | Features that are different from ASD |
| Understanding and use of language is affected | Children with ID show more social interest and reciprocity than those with ASD |
| Play is often poor or delayed | Children with ID show social imitation |
| Social interaction is often limited | Sensory sensitivities and over focussed interests are more marked in ASD |
| Making friends is difficult | Social skills impairment becomes apparent at a later age in ID |
| Children with combined ASD and ID are more withdrawn, aloof, self-injurious and ritualistic than those with just ID. | |
Developmental coordination disorder (DCD)
| Presenting features that make it look like ASD | Features that are different from ASD |
| Poor sense of personal space | Children with DCD have good communicative intent and reciprocity and their language is not disordered. |
| Clumsiness | Children with DCD have normal imaginative play. |
| Difficulties with peer relationships. | Sensory sensitivities and over focussed interests seen in ASD are not seen in DCD. |
| Some children with ASD may get a diagnosis of DCD first because of their clumsiness. | |
Attention deficit and hyperactivity disorder (ADHD)
| Presenting features that make it look like ASD | Features that are different from ASD |
| Hyperactivity, poor attention and impulsivity | In ASD the child gives sustained attention to own interests |
| Interrupting and intruding in conversations and activities | In ADHD social norms are understood, though may not be followed |
| Poor awareness of danger | In ADHD the child is exposed to danger due to impulsivity; in ASD there is poor understanding of risks. |
| Difficulties with peer relationships | In ADHD the child has social interest and can demonstrate social reciprocity |
| ADHD commonly coexists with ASD; they are not mutually exclusive. | |
Anxiety disorder
| Presenting features that make it look like ASD | Features that are different from ASD |
| Repetitive questioning or seeking of reassurance | In ASD the repetitive questions or statements have an insistent and stereotyped quality e.g. asking about time or age; often the answers to these questions must be given in the same way to be accepted by the child. |
| Social avoidance | In Anxiety the social avoidance is based more on the fear of being judged or some other fear; in ASD social avoidance is due to a lack of interest. |
| Anxiety is commonly present in children with ASD; they are not mutually exclusive. | |
Selective mutism (SM)
| Presenting features that make it look like ASD | Features that are different from ASD |
| Lack of communication in social settings | Normal communication and social interaction present at home in SM |
| History of language delay may be present | Normal imaginative play in SM |
| Anxiety is seen in social settings | No repetitive behaviour, over focussed interests, sensory or motor mannerisms in SM. |
Obsessive compulsive disorder (OCD)
| Presenting features that make it look like ASD | Features that are different from ASD |
| Obsessive, ritualistic and repetitive behaviour pattern. | The onset of OCD is usually after 4 years of age. |
| Social communication and reciprocity are normal in OCD | |
| In OCD the behaviours are distressing for the child e.g. having to repeatedly wash hands. | |
| In ASD the routines are more about insistence on sameness. | |
| OCD can co-occur with ASD. | |
Severe behaviour problems (oppositional defiant disorder (ODD) or conduct disorder)
| Presenting features that make it look like ASD | Features that are different from ASD |
| A lack of concern or empathy for others and a lack of remorse | In ODD the child understands the nature of behaviour but justifies, and deliberately persists |
| Poor peer relationships | In ODD behaviour can be modified when the child is motivated |
| In ODD there are often no repetitive behaviours with normal early development of social skills. | |
| In ASD the focus is the behaviour with no awareness of its impact. | |
| Severe behavioural problems can co-occur with ASD. | |
Attachment disorder (AD)
| Presenting features that make it look like ASD | Features that are different from ASD |
| Unusual, odd or disinhibited social behaviour e.g. becoming overfriendly with strangers. | Child with AD seeks social attention through their disinhibited behaviour; in ASD there is no such seeking. |
| Being negative or withdrawn from parents particularly with a lack of reaction or odd reaction at separation or reunion. | In AD the imaginative play is normal and there is lack of intense or unusual interests |
| There is a history of maltreatment/abuse in AD |
Rett Syndrome (RS)
| Presenting features that make it look like ASD | Features that are different from ASD |
| Regression of language skills with loss of social communication behaviour around the 1st birthday | Loss of purposeful hand movements, general motor skills and ataxia are seen in RS, not in ASD. |
| Stereotyped hand movements | Autistic hand and finger mannerisms are different from the “hand-wringing” in RS |
| Social interest is relatively preserved in RS | |
| In Rett syndrome MECP2 mutation is confirmed on testing | |
| Mild RS is more likely to be associated with ASD. | |
Epileptic Encephalopathy (EE)/ Landau Kleffenr Syndrome (LKS)
| Presenting features that make it look like ASD | Features that are different from ASD |
| Loss of language, broad development skills and social impairment in early childhood | Onset of LKS is between 2 and 7 years after a period of normal development |
| Absence seizures may be mistaken for social withdrawal | Social interest and play is relatively preserved in LKS |
| There are no preoccupations, over-focussed interests, sensory or motor mannerisms in LKS | |
| Specific EEG findings in LKS |
Severe visual impairment (VI)
| Presenting features that make it look like ASD | Features that are different from ASD |
| Lack of communicative eye contact, facial expressions and gestures and joint attention. | Social interest, effort and reciprocity is present in VI |
| Delayed language, play skills and persistence of echolalia | Children with VI want to share their interest with others and have good exploratory play |
| Narrow range of interests | Children with VI express empathy |
| Repetitive mannerisms may be present | Motor mannerisms are different: eye pocking and rocking are seen more in VI |
| ASD and severe VI can co-occur | |
Severe hearing impairment (HI)
| Presenting features that make it look like ASD | Features that are different from ASD |
| Delayed understanding and use | Social interest, initiation and reciprocity are intact in HI |
| Social awkwardness and isolation | Imaginative play is intact in HI |
| Non-verbal communication is good in HI | |
| No rigidity or repetitiveness seen in HI | |
| ASD and severe HI can co-occur. | |
Co-existing conditions with ASD
The following is the prevalence of the main co-existing conditions:
| Conditions | Prevalence (%) in children with classical autism | Prevalence (%) in children with ASD | Population prevalence |
| Intellectual disability | 76 | 65 | 3-14/1000 |
| ADHD | 41 | 45 | 3-5% |
| Anxiety | 62 | 27 | |
| Self-injurious behaviour | 49 | Not known | |
| OCD | 37 | 8 | |
| Depression | 14 | 9 | |
| Seizures | 24 | 15 | |
| Tourette syndrome | Not known | 12 | |
| Cerebral palsy | 5 | 5 | 2/1000 |
| Sleep problems | 37 | 61 | |
| Gastrointestinal problems | 3 | 62 | |
| Vision deficits | 7 | 6 | 2/1000 |
| Hearing deficits | 3 | 8 | 1/1000 |
[i] Autism spectrum disorder in under 19s: recognition, referral and diagnosis. CG 128. NICE: Sept 2011.
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