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

Background: 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. Aim: 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. Methods: 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. Findings: 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. Recommendations: 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. Conclusion: 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.