Differential Diagnoses of an Autism Spectrum Disorder

What is Autism Spectrum Disorder (ASD)?

ASD is a clinical condition with ‘persistent impairment in social interaction and social communication abilities along with restricted and repetitive patterns of behaviour’. These predominant features of ASD should be present from early childhood, according to the DSM-5, a diagnostic manual of the USA that is used worldwide. 

I have listed some of the warning signs or pointers to ASD that parents can look out for, right from the first few months of infancy, in my previous article.

Why is making a diagnosis of ASD difficult and time-consuming?

As the name implies, Autism Spectrum Disorder is a varied condition, that means, the above clinical features are present on a continuum with very mild impairment at the top end of the scale to more severe impairment of the above functions at the bottom end. 

More importantly, there are several clinical conditions, described below, that share some the features of ASD. Hence it is unsurprising that they can mistakenly be labelled as ASD. To complicate things further, many of the below-mentioned conditions can commonly co-occur with ASD. Therefore, as you can appreciate, because of the complexities involved, even the experts can get it wrong. 

Moreover, as ASD is a lifelong diagnosis and since a wrong diagnosis can lead to suboptimal or poor outcomes for the child and the family, it becomes imperative to undertake a detailed evaluation to arrive at the diagnosis of ASD, and to rule out the possibility of the below-mentioned conditions that can mimic as ASD. 

Therefore, it is crucial to undergo a thorough diagnostic evaluation, and I shall cover this is in my next article.

What does the ‘differential diagnosis’ mean?

Differential diagnosis simply means that there is more than one possibility for a diagnosis. Oxford Dictionary describes ‘differential diagnoses’ (plural noun) as ‘the process of differentiating between two or more conditions which share similar signs or symptoms.’

So, what are the differential diagnoses for ASD, then?

Following are some of the conditions that can mimic or present as ASD. I have listed them in no particular order. However, conditions in the top half of the list need to be considered more often than the conditions in the bottom half.

1. Learning Disability/Intellectual Disability (LD/ID): Learning disability is the term more commonly used in the UK (and our colleagues in the US, use the term ID or intellectual disability), for any child with significant global developmental delay. Reflecting on my experience, LD/ID must be at the top of my list because of at least two crucial reasons. Firstly, many children with ASD can have a degree of LD, making the need for carrying out a developmental assessment as part of ASD evaluation, vital. Second, it is common to get children with LD confused as having ASD, as children with LD engage in repetitive behaviours for a variety of reasons. Carrying out a developmental assessment will reveal that the language abilities of children with LD are in keeping with their cognitive ability. Moreover, children with LD have better non-verbal communication ability and a reasonable degree of emotional reciprocity, while children with ASD do not.
2. ADHD: It is common for children with ASD to be confused with ADHD. Temper tantrums and repetitive behaviours can be mistaken with hyperactivity. And avoidance of eye contact can be confused with inattention. However, children with ADHD are likely to be impulsive and domineering. They have better abilities for imaginative play and have the intent to communicate their needs. Children with ASD, on the other hand, are likely to be remote, aloof and have impaired intent and ability to communicate their needs. It is crucial to remember that both ASD and ADHD can co-occur.
3. Social Communication Disorder (SCD): It is easy to confuse children with SCD as having ASD because children in both these conditions have impaired verbal and non-verbal communication abilities. However, as DSM-5 manual has specified, unlike children with ASD, SCD children do not have restricted and repetitive patterns of behaviour and activities.
4. Gifted and Talented: Children who are gifted and talented have high intelligence and incredibly good memory. These children, when they have co-existing anxiety, can mimic ASD. Nevertheless, children who are gifted and talented seek social interactions and have good ability to understand and use language appropriate to social context.
5. Anxiety: Anxiety can be a common co-morbidity in children with ASD. Children with a social anxiety disorder or selective mutism can have several features that overlap with ASD. However, unlike children with ASD, these children have good imaginative play skills and are better able to communicate their needs to their parents and carers.
6. Language Disorder: Children with language disorder differ from ASD, in that, they have better motivation and intention to communicate their needs. Their non-verbal communication abilities are not impaired to the same extent as children with ASD. Also, unlike ASD, they have a better imaginative play.
7. Hearing Impairment: It is common for parents of children with ASD, to wonder whether their child is deaf or hearing impaired. This is because, like children with ASD, children with hearing impairment display a lack of response to their name being called, have minimal babbling, and have difficulty in using language to communicate their needs. But unlike ASD, children with hearing impairment can have a good imaginative play, have good eye contact, and can express themselves with a range of gestures, facial expressions, and body language.
8. Attachment Disorder: A history of significant parental deprivation and or neglect in early months and years is an important feature in the history of children with attachment disorder, that is absent in children with ASD. Also, children with attachment disorder develop their social interaction and language abilities when they are placed in a suitable caregiving environment.
9. Regression and Rett’s: The term ‘regression’ is used, when there is a history of a child losing hand skills and or speech and language abilities, they had previously acquired. This can understandably be genuinely concerning to parents. Rett’s syndrome is a clinical condition that occurs specifically in girls, because of a mutation in a specific gene called MECP2. In this condition, girls who appeared to be developing typically, lose speech and their ability to use hands for daily activities. Rett’s syndrome, along with childhood disintegrative disorder, are no longer classed under Autism Spectrum Disorder when DSM was revised, in 2013.
10. Genetic disorders and Syndromic: There are over a dozen syndromes that have overlapping features with ASD. Also, ASD tends to occur more commonly with certain conditions such as Fragile X, Foetal Alcohol Spectrum Disorder, Down Syndrome, etc. A detailed assessment by a neurodevelopmental paediatrician can identify these conditions.
11. Inherited Metabolic Disorder (IMD): Children with disorders of carbohydrate and protein metabolism could present with a learning disability, hearing impairment, vision impairment, developmental regression, and food intolerance. Presence of an IMD in children with ASD is fortunately rare.
12. Epilepsy: Certain epilepsy such as Landau Kleffner Syndrome (LKS), though rare, can present with the child losing the ability to understand language, display behavioural outbursts and have temper tantrums. An EEG (electroencephalogram/tracing of the brain) can help identify seizures, as the cause of ASD like symptoms.
13. Tourette’s: Children with Tourette’s syndrome and accompanying ADHD symptoms can be misinterpreted to have ASD, because of impaired social interaction skills and social communication skills secondary to sudden utterances, brief but repetitive tics, etc.
14. Obsessive-Compulsive Disorder (OCD): Both ASD and OCD can have similar symptoms. However, unlike ASD, children with OCD have better social interaction and social communication skills. Also, unlike children with ASD, children with OCD tend to find their symptoms distressing.
15. Sensory Processing Difficulties (SPD): SPD was not part of the diagnostic criteria for ASD until the latest revision to DSM in 2013. Inclusion of SPD as one of the features for the diagnosis of ASD has been helpful, as I encounter some degree of sensory difficulties almost universally in children with ASD. Children with SPD can be either hypersensitive or hyposensitive to a variety of sensations of sound, sight, smell, touch, and movement. Hence, children with SPD can be sensory seeking or extremely avoidant of certain sensations, resulting in some to mistakenly think them as having ASD. SPD is not recognised as a separate clinical disorder in DSM-5.
16. Vision Impairment (VI): Children with vision impairment can have features that mimic ASD because of certain qualitative differences in their social approach, social interaction, communication, and restrictive behaviours. However, it is important to note that VI and ASD can co-occur.

As you can see, the above list includes many conditions that need to be thought of, considered, and ruled out, before a diagnosis of ASD can be made. Nevertheless, this list is by no means exhaustive. Therefore, a comprehensive diagnostic evaluation is essential for an accurate diagnosis of Autism Spectrum Disorder. 

I shall cover the diagnostic evaluation of ASD in my next article.

References:

1. Hyman SL, Levy SE, Myers SM. Identification, Evaluation and Management of Children with Autism Spectrum Disorder. American Academy of Paediatrics, Council on Children with Disabilities, Section on Developmental and Behavioural Paediatrics. PEDIATRICS Volume 145, number 1, January 2020.
2. Zwaigenbaum L, Penner M. Autism spectrum disorder: advances in diagnosis and evaluation. State of the Art Review. BMJ, May 2018. 
3. National Institute for Health and Care Excellence. Autism spectrum disorder in under 19s: recognition, referral, and diagnosis. Clinical guideline [CG128]. September 2011, last updated December 2017. https://www.nice.org.uk/guidance/cg128
4. Dover CJ, Le Couteur A. How to diagnose autism. Arch Dis Child 2007; 92:540
5. Augustyn M, Erik von Hahn L, Patterson M, Bridgemohan C, Torchia MM, Autism spectrum disorder: Evaluation and diagnosis. UpToDate. Updated Jul 2019 accessed Jan 2020.
6. Gada S. Community Paediatrics. Oxford Specialist Handbook in Paediatrics. Oxford University Press. ISBN 978 0 19 969695 6. Published Sept 2012.