Diagnostic inflation in autism spectrum disorder: an epistemological and methodological reappraisal

The reported prevalence of Autism Spectrum Disorder (ASD) has risen nearly fourfold over two decades, fuelling debate about whether DSM-5 boundaries still demarcate a coherent clinical category. Between 2020 and 2025, multiple independent research groups have produced a convergent body of critical reflection on this question.

This narrative review is an argumentative reappraisal addressing three convergent failures - classificatory, sociocultural, and methodological - and asking what minimum evidentiary standards should govern adult ASD differential diagnosis in complex cases. Four sub-themes traditionally treated separately (sensory profile, female phenotype, personality-disorder differential diagnosis, care-pathway implications) are presented as convergent illustrations of one underlying problem.

Narrative integration of peer-reviewed publications (2015-2026) on ASD diagnostic validity, phenotypic and genetic heterogeneity (Type I/Type II partition; Litman et al. SPARK analysis), sensory processing specificity, female phenotype and camouflaging, and differential diagnosis with seven conditions: Borderline, Avoidant, and Schizotypal Personality Disorders; Complex PTSD; ADHD with affective dysregulation; Bipolar Spectrum; OCD-spectrum disorders; and adult disorganised attachment. Literature-identification methods and AI-assisted search with author verification are detailed in Section 1.3.

The category aggregates at least two neurobiologically distinct phenotypes - Type I, prototypical, often syndromic, with high genetic load; and Type II, polygenically driven, milder, overlapping with general psychopathology - differentially affected by routine-assessment limitations. The DSM-5 sensory criterion, though neurobiologically grounded, lacks diagnostic specificity. The cross-sectional, single-source, self-report-based model dominating practice is structurally inadequate for Type II presentations and the female phenotype.

Six minimum standards are specified: structured developmental history with ≥2 informants; multi-context behavioural observation; neuropsychological profiling; granular sensory assessment by modality, direction, and contextual stability; systematic evaluation of alternative diagnoses; and longitudinal formulation with revisability. Specialised pathways should use stepped multidisciplinary triage when differential diagnosis remains unresolved, directing individuals to appropriate parallel or alternative services rather than denying care. A minimum feasible standard for under-resourced settings is articulated alongside the ideal one.

Restoring diagnostic specificity to ASD is not opposed to the neurodiversity framework. It is the precondition for ensuring that the diagnostic label, when applied, identifies a population for which evidence-based interventions exist and the care pathway is appropriate.