Lucan · Conditions

Neurodevelopmental disorders — autism, ADHD, and developmental delay

Australian guidance: Autism CRC National Guidelines (Assessment and Diagnosis, 2023 update; Supporting Autistic Children, 2022) + eTG Psychotropic — ADHD + AADPA Australian Evidence-Based Clinical Practice Guideline for ADHD (2022)

1. Definition and epidemiology

Developmental delay exists on a spectrum from domain-specific delay, in which a single stream of development lags behind the expected trajectory while other domains proceed normally, through to global developmental delay (GDD), in which significant delay is present across two or more domains in a child younger than 5 years (the term is not applied beyond this age because standardised cognitive testing is not reliably valid before it). For the purpose of triaging a referral, this file groups milestones into four clinically actionable domains: gross motor; fine motor and vision; speech/language and hearing; and social/emotional/behavioural. These four groupings condense the six RACGP surveillance domains covered in the companion developmental-milestones file into the paired categories clinicians use when deciding which specialty pathway to activate; the milestone ages themselves are not repeated here. A developmental disorder, by contrast to delay, describes a persistent and qualitatively atypical pattern of development, such as autism spectrum disorder (ASD) or attention deficit hyperactivity disorder (ADHD), that does not simply resolve with the passage of time.

Australia's most recent published national estimate (Australian Institute of Health and Welfare, drawing on the 2015 Australian Bureau of Statistics Survey of Disability, Ageing and Carers) places autism prevalence at approximately 1 in 150 people (about 0.7%), with males approximately four times as likely as females to be reported as having autism; diagnosis rates in children have risen substantially since 2009, and more recent clinical and service-linked estimates suggest this figure now understates true prevalence. ADHD affects 5 to 7% of Australian school-aged children. Cerebral palsy (CP), a permanent disorder of movement and posture arising from a non-progressive disturbance in the developing fetal or infant brain, affects approximately 2 per 1000 live births in Australia. Intellectual disability prevalence is covered in the companion developmental-milestones file and is not repeated here.

2. Pathophysiology

For the synaptic and connectivity basis of ASD, see the companion developmental-milestones file (Robbins Ch 10). This file adds the pathophysiology of ADHD, intellectual disability, and cerebral palsy. ADHD is understood as a disorder of frontostriatal circuit dysregulation, with reduced dopaminergic and noradrenergic tone in the prefrontal and striatal networks responsible for inhibitory control, sustained attention, and executive function. Longitudinal imaging studies demonstrate a delay of several years in attaining peak cortical thickness, particularly in the prefrontal cortex, relative to typically developing children, consistent with a maturational lag rather than a fixed structural lesion; twin studies place heritability at 70 to 80%, among the highest of any psychiatric condition. Intellectual disability arises from heterogeneous mechanisms, including chromosomal and single-gene disorders, prenatal teratogen exposure, perinatal hypoxic-ischaemic injury, and postnatal insults, converging on reduced neuronal density and simplified dendritic arborisation (Robbins Ch 10); despite comprehensive investigation, a specific cause remains unidentified in a substantial proportion of cases. Cerebral palsy results from a single, non-progressive insult to the developing brain occurring antenatally (structural malformation, in-utero stroke, congenital infection), perinatally (hypoxic-ischaemic encephalopathy, intraventricular haemorrhage or periventricular leukomalacia, particularly before 32 weeks' gestation), or postnatally up to approximately 2 years of age (kernicterus, meningitis, traumatic brain injury). Although the causative brain lesion in CP does not progress, the clinical phenotype evolves as the child grows, and secondary musculoskeletal complications such as contractures can worsen over time even though the underlying injury remains static; this distinguishes CP from a genuinely progressive or neurodegenerative process.

3. Clinical presentation and diagnostic criteria

Absolute red flags mandating referral, irrespective of an otherwise reassuring history, are no social smile by 6 to 8 weeks, no sitting unsupported by 9 months, not walking independently by 18 months, no words by 18 months, no two-word phrases by 2 years, and any loss of previously acquired skills at any age (RCH Melbourne Developmental CPG). Developmental delay describes a child progressing through the typical developmental sequence at a slower rate, with the expectation that milestones will eventually be achieved; developmental disorder describes a persistent, qualitatively atypical pattern that does not resolve simply with time and requires targeted diagnosis. Regression, the loss of previously acquired skills, is categorically different from either delay or disorder: it is never a normal variant and signals an active process, whether an epileptic encephalopathy, a neurodegenerative or metabolic disorder, or an evolving structural lesion, and therefore mandates urgent rather than routine assessment.

ASD is diagnosed against DSM-5-TR criteria across two core domains. Domain A requires persistent deficits in social communication and social interaction across multiple contexts, encompassing all three of: deficits in social-emotional reciprocity; deficits in nonverbal communicative behaviours used for social interaction (eye contact, gesture, facial expression); and deficits in developing, maintaining, and understanding relationships. Domain B requires restricted, repetitive patterns of behaviour, interests, or activities, meeting at least two of four: stereotyped or repetitive motor movements, use of objects, or speech; insistence on sameness and inflexible adherence to routines; highly restricted, fixated interests abnormal in intensity or focus; and hyper- or hyporeactivity to sensory input. Symptoms must be present in the early developmental period, although they may not become fully apparent until social demands exceed the child's capacity, and must cause clinically significant functional impairment not better explained by intellectual disability or global developmental delay alone. Early signs recognised before 18 months include reduced response to name, absent or reduced joint attention (pointing to share interest rather than only to request), limited eye contact, and absent pretend play; a subset of children show a clear regression in language and social engagement during the second year of life. Severity is graded separately for each domain, from Level 1 (requiring support) to Level 3 (requiring very substantial support).

ADHD is diagnosed against DSM-5-TR criteria for a predominantly inattentive presentation (6 or more of 9 inattentive symptoms, or 5 or more from age 17), a predominantly hyperactive-impulsive presentation (6 or more of 9 hyperactive-impulsive symptoms, or 5 or more from age 17), or a combined presentation, each present for at least 6 months to a degree inconsistent with developmental level. Diagnosis additionally requires that several symptoms were present before age 12, that impairment from symptoms is evident in 2 or more settings (for example home and school), that there is clear evidence the symptoms interfere with social, academic, or occupational functioning, and that the presentation is not exclusively explained by another psychiatric disorder (eTG Psychotropic). Diagnosis in Australian children requires a comprehensive assessment incorporating medical, developmental, and psychosocial information from multiple informants; parent and teacher rating scales assist in gauging severity and monitoring treatment response but are not diagnostic in isolation.

Intellectual disability, per DSM-5-TR, requires deficits in intellectual functions (reasoning, problem-solving, abstract thinking, judgement, academic learning) confirmed by standardised testing, together with deficits in adaptive functioning that limit independence in one or more domains (conceptual, social, practical) across multiple settings, both with onset during the developmental period. Severity (mild, moderate, severe, profound) is graded by adaptive functioning rather than by intelligence quotient score alone, because adaptive functioning determines the level of support required.

Cerebral palsy presents with early motor red flags including asymmetric hand use before 12 months, persistently increased or decreased tone, persistence of primitive reflexes beyond the expected age, and delayed gross motor milestones. It is classified by the dominant movement disorder (spastic, the most common pattern; dyskinetic; ataxic; or mixed) and by limb distribution (hemiplegia, diplegia, quadriplegia), with functional severity graded using the Gross Motor Function Classification System (GMFCS, levels I to V).

4. Investigations and AU-specific cutoffs

In any child presenting with speech or language delay, audiological assessment must be arranged before any other investigation or referral pathway is pursued, because hearing loss, including reversible middle-ear disease, is the most common cause of apparent language delay and can confound the assessment of social communication in every other domain, including a suspected diagnosis of ASD. Vision screening should be arranged alongside or immediately after hearing assessment for the same reason.

For global developmental delay, once hearing and vision have been assessed and excluded as contributing factors, chromosomal microarray is the recommended next-tier investigation, having replaced conventional karyotype as the first-line genetic test because it detects clinically significant copy number variants even in children without dysmorphic features. Fragile X polymerase chain reaction testing is added when there is a family history of intellectual disability or autism, or examination findings such as macroorchidism, a long face, or prominent ears, particularly in males, because fragile X syndrome is the most common inherited cause of intellectual disability. Metabolic screening (plasma amino acids, urine organic acids, ammonia, lactate) and thyroid function testing are added when there are additional red flags such as consanguinity, dysmorphic features, or a suggestive family history; congenital hypothyroidism is otherwise captured by the newborn heel-prick screening programme. MRI brain is reserved for children with focal neurological signs, an abnormal head circumference trajectory, seizures, or regression, rather than being used routinely in isolated global developmental delay without these features, given its low diagnostic yield in that context.

Regression at any age is managed as a distinct, urgent pathway rather than following the standard GDD cascade: electroencephalogram to identify an epileptic encephalopathy, an expanded metabolic screen, and MRI brain are indicated together with urgent paediatric neurology referral, reflecting the possibility of an actively progressive or treatable underlying process.

There is no diagnostic biomarker for ASD; diagnosis is clinical, made through a Diagnostic Evaluation conducted under the Australian national guideline by a Lead Practitioner (a medical practitioner with specialist registration in community child health, general paediatrics, psychiatry, or neurology, or an appropriately credentialled psychologist), ideally with input from at least one other discipline, or by a Consensus Team of two or more practitioners when the presentation is complex or a Lead Practitioner assessment is inconclusive (Autism CRC National Guideline for the Assessment and Diagnosis of Autism in Australia). Before starting pharmacotherapy for ADHD, baseline height, weight, heart rate, and blood pressure should be recorded (eTG Psychotropic).

5. Management

Once developmental concerns are confirmed, referral in Western Australia typically proceeds through the Child Development Service, a general or developmental paediatrician, speech pathology, and audiology, selected according to the domains affected; audiology is actioned first whenever speech or language delay is a presenting feature, for the reasons given above. Children with a confirmed delay, or significant concerns short of a formal delay diagnosis, are eligible for the NDIS early childhood approach, which funds early intervention supports without requiring a definitive diagnostic label.

Management of ASD is multidisciplinary and individualised, incorporating speech pathology, occupational therapy, and educational planning. Current Australian national guidance (December 2022) frames intervention as evidence-based and neurodiversity-affirming, prioritising individually meaningful, strengths-focused goals over a single mandated therapy model; Naturalistic Developmental Behavioural Interventions, in which skills are taught through interaction within everyday activities and environments, are one example of an approach consistent with this framework. The GP's role is to facilitate timely referral, support the family through the diagnostic process, and monitor for co-occurring conditions.

Management of ADHD follows an individualised multimodal plan agreed with the child, family, and teachers. Nonpharmacological strategies are first-line and include psychoeducation, social and organisational skills training, parent behaviour training, and classroom management measures; routine dietary modification or supplementation is not indicated unless a specific food sensitivity is identified (eTG Psychotropic). Pharmacotherapy is added according to age and severity as part of the same individualised plan, prescribed by a clinician experienced in paediatric psychotropic use, with the need for ongoing treatment reviewed at least annually.

Cerebral palsy management is multidisciplinary (physiotherapy, occupational therapy, speech pathology) and targets function, spasticity, and secondary musculoskeletal complications; detailed CP management is beyond the scope of this file.

6. Pharmacology and AU PBS notes

Stimulants (methylphenidate, dexamfetamine, lisdexamfetamine) are first-line pharmacotherapy for ADHD in Australian children aged 6 years and older; use below 6 years is reserved for exceptional circumstances under specialist supervision (eTG Psychotropic). Short-acting methylphenidate is typically initiated at 5 mg orally once or twice daily, titrated in 5 to 10 mg increments at weekly intervals to a usual maximum of 60 mg per day (rarely above 2 mg/kg); once an effective dose is established, patients often transition to a long-acting formulation providing either an 8-hour (for example Ritalin LA) or 12-hour (for example Concerta) duration of effect. Dexamfetamine is initiated at 2.5 mg once or twice daily, titrated in 2.5 mg increments to a usual maximum of 40 mg per day. Lisdexamfetamine, a prodrug requiring enzymatic cleavage to release active dexamfetamine, is dosed once daily in the morning, starting at 30 mg and titrated in 20 mg increments to a maximum of 70 mg per day; its prodrug mechanism produces a smoother onset and is considered to carry a lower misuse potential than immediate-release stimulants. There is no clear evidence that one stimulant is more effective than another for a given child; a child who does not respond to or tolerate one stimulant may still respond to another, and doses are given with or immediately after meals to reduce the anorectic effect, avoiding late evening doses to reduce insomnia.

Non-stimulant options are used when stimulants are unsuitable, poorly tolerated, or carry a risk of misuse, or when there is comorbid Tourette syndrome or severe anxiety. Atomoxetine, a selective noradrenaline reuptake inhibitor, is dosed by weight, starting at 0.5 mg/kg/day and increasing to a target of 1.2 mg/kg/day. Guanfacine, an alpha-2A adrenergic agonist, is started at 1 mg at bedtime and titrated by 1 mg weekly; it is also useful as an adjunct to a stimulant with an inadequate response, or in children with a comorbid tic disorder. Clonidine has a similar role but requires multiple daily dosing due to its short half-life and must be tapered gradually to avoid rebound hypertension.

The most common adverse effects of stimulant therapy are appetite suppression, managed by dosing with or after meals, and a small effect on growth velocity; height and weight should be monitored at every review, with a planned drug-free interval (for example weekends or school holidays) considered if growth becomes a genuine concern. Stimulants and atomoxetine can also affect heart rate and blood pressure, warranting monitoring at baseline and each review, with electrocardiogram reserved for a clinically significant change. Prescribers must follow state and territory regulations governing stimulant prescribing, as these medicines are Schedule 8 controlled drugs in Australia.

For pharmacological management of comorbid conditions in ASD and global developmental delay (anxiety, sleep disturbance, epilepsy, severe behavioural dysregulation), see the companion developmental-milestones file; this is not repeated here.

7. Complications and monitoring

ADHD pharmacotherapy is reviewed monthly during initial titration, then at least a few times a year once stable, assessing symptom control, growth, cardiovascular parameters, adverse effects, comorbidities including substance use in adolescents, and adherence; family contact with the child's school before review appointments assists in gathering functional information (eTG Psychotropic). Untreated or delayed-diagnosis ADHD and ASD carry a substantially increased risk of academic underachievement and mental health comorbidity. Transition planning to adult services for young people with ASD or intellectual disability is addressed in the companion developmental-milestones file and is not repeated here.

Complications specific to cerebral palsy include hip subluxation and dislocation, requiring surveillance hip radiographs on a schedule determined by GMFCS level, progressive scoliosis, contractures, feeding difficulty with aspiration risk, and epilepsy, which affects approximately one-third of children with cerebral palsy.

Children with an initial diagnosis of global developmental delay require longitudinal follow-up, because outcomes are heterogeneous: some children subsequently demonstrate a typical trajectory, while others are later confirmed to have a specific diagnosis, including intellectual disability, once formal cognitive testing becomes valid from approximately age 5.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.