Approach
ASD is a clinical diagnosis made by pediatricians, child psychiatrists, adult psychiatrists or psychologists, and other professionals, often working in multidisciplinary teams; specific training in the diagnosis and management of ASD is essential for those making a diagnosis. Specialists therefore make this diagnosis according to standardized clinical criteria. Diagnosis relies on gathering information about functioning in more than one environment (e.g., school/work and home).[29][87] More than 80% of children with ASD show clear behavioral signs by the age of 24 months, and there are a number of red flags in the domains of social and language development and patterns of play and behavior in 12- to 18-month-old children that would alert a parent or community surveillance health professional to the need for further assessment.[88] Many behaviors suggestive of ASD are often seen among typically developing young children, at different stages in their development. Nonetheless, the presence of red flags should always be taken seriously by professionals, and the child should be referred to someone with expertise in ASD. Early diagnosis is beneficial to allow for early intervention for the child and genetic counseling for parents. In adults, the diagnosis can be made at any age, including older age, provided an informant is available who can comment on the individual's developmental history.
Be mindful of, and try to mitigate against, any potential barriers to diagnosis. Anecdotally, people with ASD and their parents report frequent challenges and delays in the diagnostic process, typically describing it as a "battle". This can be a particular problem for girls and women, who may present differently to males, and who are often adept at masking the symptoms of autism.[89] There may also be the misconception, even amongst clinicians, that ASD is a male disorder. Evidence suggests that females are less likely than males to receive a diagnosis, despite comparable levels of symptom severity.[90][91] Evidence also suggests that black children with ASD are more likely than white children to receive a delayed diagnosis, or be misdiagnosed (e.g., with a conduct or adjustment disorder).[92]
Family history
In a small number of families in which there is a person with ASD, there may be other relatives with ASD or another ASD-related disorder. More commonly, parents or other first- or second-degree relatives might have specific learning difficulties such as in reading, writing, or spelling. Some parents and siblings of children with ASD recognize that they themselves have relatively mild behavioral or personality traits that relate to ASD; when not associated with an ASD diagnosis, these difficulties are known as the broader autism phenotype (BAP).[55][93] BAP is not a clinical diagnostic term. Consequently, it should not be used in a clinical setting without being appropriately elaborated. Instead, the exact nature of vulnerability should be described among such individuals. For example: "He recognizes that he has some of the social communication difficulties and rigidity associated with ASD; however, these difficulties are not significant enough for a diagnosis of ASD and do not lead to the degree of impairment seen in people with a clinical ASD diagnosis. Nonetheless, support at school, at college, and in the workplace may be required; strategies of the type used with people with ASD may be useful."
Presentation in children
ASD is clinically very heterogeneous. It manifests differently in children depending on a number of factors that include age, language, and cognitive abilities. Core symptoms occur in two domains: social communication/interaction and restricted, repetitive patterns of behavior.[1]
In children, consider the possibility of ASD if there are concerns about development or behavior, and always take parents’ and carers’ concerns seriously, even if these concerns are not shared by others.[12] Parents are often the first to detect early signs of autism in children, most frequently expressing concerns relating to language (e.g., delay) and communication.[94]
The list below outlines some common presenting features of ASD in children of different ages, but be aware that manifestations of ASD vary substantially between individuals. Note that many of the features described below are not specific to autism, and may occur in children without ASD.
General features
Infants (0-2):
May be quiet and placid; or very upset, irritable, and difficult to put down[95][96]
May be distressed if not being carried around.
Preschoolers (2-4):
Behaviors that occur in the first 2 years may persist to varying degrees.
Older children:
Core symptoms of ASD may contribute to conflict at home and in the educational environment, as well as worsening social exclusion and the onset of mental health problems
Older children may develop conflict with parents and school staff.
Eating and drinking
Infants (0-2):
May be difficult to feed, refuse bottles, and/or difficult to wean onto solids
May be distressed by the taste of food, or by the sensation of a spoon in their mouth or food around their lips.
Preschoolers (2-4):
Behaviors that occur in the first 2 years persist to varying degrees; sensitivity to certain types of foods or food textures, or the way food is arranged on a plate, may continue throughout life.
Older children:
Older children with ASD may have restricted and ritualistic behaviors in relation to eating and drinking.[97]
Nonverbal communication
Infants (0-2):
May be reduced pointing overall, or more specifically in the protodeclarative context (i.e., the use of an index finger to indicate an object of interest to another person)
There is often difficulty integrating pointing and eye gaze (i.e., adjusting gaze between the object of interest and the intended target)
There may be delayed nodding and/or shaking the head, waving, or using other gestures.
Preschoolers (2-4):
Mood may be very difficult to interpret, as children's nonverbal communication methods (e.g., eye contact, facial expression, demeanour, gesture) might not show how they feel[98]
Mood may therefore be perceived to change quickly.
Older children:
Older children with ASD frequently show the same behaviors described in younger children, to some degree
Frustration in making feelings, thoughts, and needs known to others may lead to vocal outbursts or challenging behavior.
Spoken language development
Infants (0-2):
During the first year, parents may notice that their children have delayed language development (e.g., lack of vocalization/babble)
Young children frequently have delayed single-word or phrase speech, and their articulation may be unclear.[99]
Preschoolers (2-4):
Children with phrase speech frequently use phrases they have heard others use in their daily language to a greater degree than typically developing children (stereotyped speech)
Language may be repetitive, or repetitive requests may be made for parents to say or do something in a particular way
There may be loss of previously acquired language skills (regression).[4]
Older children:
Older children with ASD frequently show the same behaviors described in younger children, to some degree
Language skills vary widely between children with ASD; some are nonverbal, others may have problems with understanding or using spoken language, and others (around 1 in 10 according to one study) achieve typical language levels[100]
Some children may develop language at a very early age and have relatively "adult-like" speech.
Social communication and play
Infants (0-2):
Children with ASD tend to use fewer facial expressions and gestures, and tend not to integrate eye contact with vocalization or nonverbal communication
Children frequently don't interact with their parents in a to-and-fro way during the first year
They may not play social games (e.g., peek-a-boo) or may not be spontaneously interested in engaging with their parents
They may be less likely to bring and show toys or books to their parents, or to play socially, than their peers
Children with ASD frequently play alone and may be relatively uninterested in being with other children
Many children have reduced eye contact; others look at their parents but don't use their eye contact socially to engage.
Preschoolers (2-4):
During the toddler years, most children prefer to play alone, or may play superficially with other children (e.g., standing with them), but engage in less to-and-fro play than expected
Some children sit alone and play with certain objects or toys for hours (often looking at them or playing nonfunctionally)
Children might play with parents or older children when items are brought to them, but often bring, show, and initiate social contact and play less than other children
While atypical development may have been present in the early years, many children only come to the attention of professionals at preschool or school age, when their social communication difficulties become more obvious.
Older children:
While atypical development may have been present in the early years, many children still only come to the attention of professionals at preschool or school age, when their social communication difficulties become more obvious
Frequently children with ASD misunderstand the subtleties of social relationships, often experiencing friendship difficulties as a result
Children may continue to struggle in peer relationships as the social demands of mid-childhood increase.
Repetitive, rigid, or stereotyped interests, behaviors, or activities
Infants (0-2):
May have particular ways of going about everyday activities, may prefer toys to be in a certain place, and become more distressed than expected if the home environment changes: for example, if furniture or other household items are moved
May collect or hoard unusual items, or show a particular interest in items that are unusual for their chronologic age.
Preschoolers (2-4):
The behaviors that occur in the first 2 years persist to varying degrees.
Older children:
Often there is a need for routine, or obsessions or interests that may be pursued in the classroom or during peer interaction
Young people may pursue their own interests to the exclusion of everything else
Difficulty with change often becomes increasingly pronounced as a child becomes older, at a time when change is frequent and often part of daily life.
Sensory behaviors
Infants (0-2):
May be more interested in the smell, taste, or feel of objects, clothes, hair, or people, and may engage in repetitive sensory behaviors in inappropriate circumstances (e.g., stroking a stranger's hair in public)
There may be sensory-related difficulties, such as a negative (and sometimes idiosyncratic) reaction to certain textures, sounds, and other sensory stimuli.[13]
Preschoolers (2-4):
The behaviors that occur in the first 2 years persist to varying degrees.
Older children:
Older children with ASD frequently show the same behaviors described in younger children, to some degree
Sensory interests may persist in the classroom and interfere with learning.
Motor stereotypes
Infants (0-2):
Children frequently show repetitive motor mannerisms, such as spinning around, bouncing up and down, flapping their hands or objects/materials, or flicking their fingers (sometimes referred to as "stimming")
May develop unusual transient stiff postures with their hands or whole bodies.
Preschoolers (2-4):
The behaviors that occur in the first 2 years persist to varying degrees.
Older children:
Motor behaviors may persist in the classroom and interfere with learning.
Note that ASD is clinically very heterogenous, and that children may still have ASD in spite of any of the following:[12]
Good eye contact, smiling, and showing affection to family members
Reported pretend play or normal language milestones
A previous assessment that concluded that there was no ASD, if new information becomes available.
Older children with ASD may be proficient at masking signs and symptoms due to compensatory mechanisms, which may be aided by a supportive environment. In particular, the diagnosis may be missed in children who are verbally able.[12][74] The presence of co-occurring conditions such as ADHD may prevent clinicians from recognizing ASD symptoms; this is associated on average with a delay in diagnosis of ASD.[101] Recognition may also be challenging in minimally-verbal children, in whom it is often difficult to assess social understanding. It may also be difficult to diagnose comorbid psychiatric disorders in children who are minimally-verbal.
Language or social skill regression may occur.[102] In a child younger than 3 years it is a red flag feature suggestive of possible ASD, and warrants a referral to a specialist team for a diagnostic assessment.[12] Regression of language skills in a child older than 3 years, or regression of motor skills at any age, should make clinicians think of other possible diagnoses, and prompt a referral to a pediatrician or pediatric neurologist.[12]
For all other children and young people with a possible diagnosis of autism, consider referral for a diagnostic assessment, taking into account:[12]
The severity and duration of signs/symptoms
The extent to which the signs/symptoms are present across different settings
The level of concern expressed by the child and/or their family
Any specific factors which may make ASD more likely
The likelihood of an alternative diagnosis.
Presentation in adults
Adults with ASD may first present to healthcare professionals at any time or age, but presentation may be more common at times of uncertainty, change, or stress, such as when transitioning to adulthood, or after bereavement.[74] ASD in adults may be identified as a cause of difficulties at home, in social relationships or in those with a partner, or in the workplace. Severity of ASD in adults varies substantially; some people require lifelong care or support, while others live independently and manage to maintain careers, family, and social lives.
Many young people and adults with ASD have concurrent mental health diagnoses, such as anxiety disorder, depression, or ADHD, and these comorbidities may be a presenting feature and have a marked negative impact on function. It is therefore recommended that ASD be routinely considered when an adult presents to mental health services with a psychiatric disorder.[103]
In adults, consider the possibility of ASD if one or more of the following are present and are deemed to have onset in childhood:[104]
Persistent difficulties in social interaction
Persistent difficulties in social communication
Stereotypical (rigid and repetitive) behaviors, resistance to change, or restricted interests
AND, if one or more of the following are present:
Problems in obtaining or sustaining employment or education
Difficulties in initiating or sustaining social relationships
Previous or current contact with mental health or learning/intellectual disability services
A history of a neurodevelopmental disorder (including an intellectual disability or ADHD) or mental health disorder.
As with older children, adults with ASD may be skilled in using adaptive mechanisms to manage social situations, which may mask their symptoms on assessment.[105][106] Other barriers to diagnosis in adults include the presence of comorbid mental health or neurodevelopmental disorders, which may complicate or overshadow the diagnosis of ASD. There may also be difficulties in obtaining an adequate developmental history from a primary caregiver.[107] Where no information is available from a primary caregiver, diagnosis should be based on the available history and current assessment, including reports from the place of employment or education.[108]
Sex-based differences in ASD presentation
ASD in girls and women is consistently under-reported relative to males.[72][73] This is potentially related to differences in presentation and levels of impairment.[74] Additionally, screening and diagnostic instruments may be less accurate at identifying the characteristics of ASD in females.[74]
Although the evidence base on sex-based differences is still in its early stages, the following has been suggested:[74]
Females may have more of a desire for social contact, friendships, and peer group acceptance than males (in spite of experiencing difficulties in developing and maintaining friendships)[109]
Girls with ASD may be more able to mask social play deficits by imitating nonaffected peers[109]
Girls’ interests may be in more socially typical domains than male interests (e.g., literature or music)[110]
Females may have better coping skills than males with equivalently high levels of autistic traits, leading to fewer, and later, diagnoses[72][73]
Females may show more subtle signs of repetitive and restrictive behaviors and interests than males[110]
Females may show less impairment in theory of mind tasks than males[109]
Females may be more likely to present with eating disorders than males[109]
Females may present as shy, perfectionistic, or "bossy" (the so-called "female autistic phenotype") traits, which do not contribute to a diagnosis of autism via established diagnostic criteria, and which are also frequently seen in people without ASD.[108]
Use of standardized interview and observational assessment tools
The ASD diagnosis should be confirmed or made by an appropriately trained professional, ideally working as part of a multidisciplinary team. There are a number of specialized assessment tools which may be useful both for screening and during diagnosis; however, it is possible for the specialist team to make a diagnosis of ASD without the use of these tools.
There are many available screening questionnaires for use with parents of children with ASD, and with adults, and with relatives.
In children, screening questionnaires may be helpful for information gathering in primary care, but the evidence is insufficient to determine whether any particular instrument is effective in detecting children more likely to have ASD.[12] They should therefore not be used as a standalone tool to determine whether a referral for assessment for ASD is required.[74] In secondary care, specialist clinicians use history and observation to make a diagnosis. A combination of the neurodevelopmental history, a standardized interview, and an observational assessment (e.g., the Autism Diagnostic Observational Schedule) is used by some clinicians to gather information leading to diagnosis.[111][112] Observation of children in school or another setting is often very helpful.[113][114]
For adults, research on the comparative strengths and weaknesses of different screening and diagnostic tools is limited. The tools typically used during diagnosis in adults are structured questionnaires (e.g., self-report, or informant-completed brief measures used as screening tools, sometimes in primary care) and diagnostic measures (e.g., more in-depth assessment tools completed by a specialist team, which generally include semi-structured interviews and interactive tasks).
There is very limited evidence to support the use of structured questionnaires for screening for ASD.[115] In general, these tools appear to have reasonable sensitivity, but limited specificity (i.e., less effective in identifying people without ASD).[107] The Autism-Spectrum Quotient - 10 items (AQ-10) is a short questionnaire recommended by the UK National Institute for Health and Care Excellence (NICE). It is designed for adults with possible ASD to guide the need for referral for a comprehensive diagnostic assessment.[104] The AQ-10 requires self-completion, and may not be suitable for people with an intellectual disability; it is recommended for use only in people with an IQ greater than 70.[74][104] One meta-analysis published in 2018, examining evidence published following the NICE guideline, found that the AQ-10 had reasonable sensitivity but low specificity. It was associated with an increased risk of false positives in the presence of mental health conditions, such as generalized anxiety disorder, and did not differentiate ASD adequately from schizophrenia suggesting that, used alone, it is not a reliable indicator of who may require a full ASD assessment by a specialist team.[116][117] Structured questionnaires in general may be useful in primary care to gather information about a possible diagnosis of ASD, but should not typically be used in isolation to rule in or out further ASD assessment.[107]
Two diagnostic measures, the Autism Diagnostic Observation Schedule-Generic (ADOS-G) and the Autism Diagnostic Interview Revised (ADI-R), are recommended for use by NICE in secondary care as part of a comprehensive assessment for adults with suspected ASD, both with and without intellectual disability.[104] The ADOS-G appears to have good sensitivity and specificity in general, although specificity is reduced in people with schizophrenia, psychosis, and personality disorder.[118][119][120][121] The ADI-R was found to have good specificity but low sensitivity in one study. NICE recommends using diagnostic tools to aid diagnosis for patients in whom the diagnosis of ASD is unclear; in this scenario, they recommend using a combination of diagnostic tools to improve accuracy, and this approach is supported by a limited amount of evidence.[104][122]
Diagnostic tools may be used where needed in conjunction with direct observation and information from other sources (e.g., family members) to give information about the adult’s early developmental history.
Clinical examination
Many children with ASD are physically healthy. Other medical conditions in which ASD is found frequently (e.g., fragile X syndrome or tuberous sclerosis) need to be specifically excluded.[123] Specialist input is typically required for interpreting results, and genetic counseling is helpful to explain the reasons for testing and the subsequent results. An underlying medical disorder (e.g., fragile X syndrome, chromosomal abnormality, tuberous sclerosis) is more commonly found in children with ASD who have learning difficulties and/or dysmorphism.[124] All children with early onset socio-communicative impairments should also have a hearing test.
It is recommended that all children should be examined with a Wood lamp on a one-off basis following diagnosis in order to search for hypopigmented macules (associated with tuberous sclerosis).[12] However, if a Wood lamp is not available, visual examination of the skin for stigmata of tuberous sclerosis should be sufficient. A full neurologic examination including measurement of head circumference is routinely performed in all children. Although macrocephaly is associated with ASD, the pathophysiological reasons for this are unclear, and the implications not well defined. There is a known association between macrocephaly and certain genetic syndromes, some of which (e.g., PTEN deletion) are associated with ASD, and so evidence of macrocephaly and accompanying dysmorphism should prompt the search for one of these syndromes.
Some people with ASD show symptoms of distress or irritability. Understanding whether the child or adult may be in pain can be challenging in the context of communication impairments, or intellectual disability. Appropriate history-taking and exam, and sometimes investigation, is required to address parent/caregiver concerns about pain.
Investigations
In some regions, such as the UK, targeted genetic testing (e.g., fragile X and clinical microarray testing) is generally offered only to children with intellectual disability, congenital abnormalities, or dysmorphism.[104][12] The rationale for restricting genetic testing to particular groups of people with ASD is that the yield of positive results is typically considered to be low in other people with ASD.[125] However, in the US and parts of Canada, genetic evaluation (including fragile X testing) is recommended to all families of children with ASD as part of the etiologic work-up.[29] Expert consensus in the US suggests that targeted genetic testing should also be offered to all children with ASD.[126] However, clinical practice varies considerably. Before ordering a genetic test, ask the patient (or parents/carers) about prior genetic testing and review the patient’s medical record.[127] Specialist input is typically required for interpreting results, and genetic counseling is helpful to explain the reasons for testing and the subsequent results. Do not order a duplicate genetic test unless there is uncertainty about the existing result (e.g., the result is inconsistent with the current clinical presentation or there is a subsequent change in the test methodology).[127]
Whole exome sequencing is a further option if clinical microarray and fragile X testing do not identify an etiology, as guided by the local specialist genetic team. When a specific genetic etiology is identified for ASD, the family can be given information about the likelihood of recurrence in subsequent siblings. Practice on genetic testing for ASD differs regionally and nationally, so clinicians should follow appropriate local guidance on testing protocols.
Electroencephalogram and MRI brain testing and additional blood/urine tests are all subsequent investigations that may be performed if there is a specific disorder suspected following the clinical history or examination. For example, nutritional blood tests if a restricted diet is identified, and M-methyl-CpG binding protein (MECP2) deletion should be a test in girls with ASD, clinical Rett syndrome features, and regression.[29] Rett syndrome is a childhood neurodevelopmental disorder characterized by normal development followed by slowed head and brain growth, gait abnormalities, loss of purposeful use of hands, intellectual disability, and seizures. Audiology may also be considered if hearing loss causing language delay has not been excluded.[29]
Do not test urine for metals and minerals or test hair for other environmental toxins in children with suspected ASD.[128] There is no evidence supporting routine testing of hair or urine for environmental toxins or heavy metals in the assessment of children with suspected ASD.[29]
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