Under-Diagnosis of Personality Disorders in Autistic Adults: What Clinicians Need to Know

By Triad Psych, P.C. — 23 Years Strong in Evidence-Based Mental Healthcare

At Triad Psych, we regularly evaluate clients whose histories are shaped by years of diagnostic complexity and clinical ambiguity. One emerging reality across the field—supported by growing research—is that personality disorders (PDs) are frequently under-diagnosed in adults with Autism Spectrum Disorder (ASD).

Missing or misattributing these co-occurring conditions can lead to treatment misalignment, misunderstandings, and preventable crises. Understanding this issue is essential to providing ethical, accurate, and effective care.

For the past 20 years our founder Dave Glick through his affiliation with the Office of National Drug Control Policy and the Atlanta Carolina’s HIDTA has trained more law enforcement and public safety professionals in the area of personality disorders than any other clinician nationwide through his class Advanced Psychology for Cops.

Diagnostic Overshadowing: A Hidden Blind Spot in Adult ASD Assessment

A central driver of under-diagnosis is diagnostic overshadowing, a cognitive bias in which symptoms of one condition (such as autism) cause clinicians to overlook additional diagnoses.

Because ASD and PD presentations can overlap, misinterpretation is common:

• Social difficulties may be attributed solely to autism, missing avoidant or schizoid PD traits.
• Emotional dysregulation may be mistaken as ASD-related when BPD traits are also present.
• Rigid thinking could reflect autism—or obsessive-compulsive or paranoid personality features.

Structured assessment and a developmental history are essential for differentiating these patterns.

What the Research Shows: Summary of Key Findings

1. PD screening is often missing from ASD evaluations.
   A 2021 systematic review found that many adult ASD assessments do not include personality-disorder screening instruments, despite high rates of PD traits among autistic adults.
2. Autism–BPD diagnostic confusion is common.
   A 2024 editorial in the British Journal of Psychiatry notes that clinicians frequently confuse BPD for ASD or fail to identify both when they co-occur.
3. PD diagnoses frequently disappear after an ASD diagnosis.
   Longitudinal studies show PDs are the most commonly dropped diagnosis once autism is identified—suggesting earlier PD misdiagnosis, but also potential PD under-recognition afterward.
4. Autistic adults report high rates of psychiatric misdiagnosis.
   Lancet-group research (2024) reports that one in four autistic adults felt they were previously misdiagnosed—often with a personality disorder.
5. Autistic adults with prior BPD diagnoses describe years of misidentification.
   Recent qualitative studies show that many autistic adults labeled with BPD experienced extended periods of misunderstanding before receiving an accurate ASD diagnosis.

Practice Recommendations for Clinicians

At Triad Psych, we recommend these strategies based on research and clinical experience:

1. Screen for PDs in adult ASD evaluations.
   Use SCID-5-PD, SAPAS-SR, or dimensional personality measures when indicated.
2. Distinguish neurodevelopmental traits from later-emerging personality patterns.
   Developmental formulation is crucial for accurate diagnostic clarity.
3. Avoid automatic diagnostic substitution.
   Autism and PDs can and do co-occur; dropping a PD diagnosis prematurely may obscure important treatment needs.
4. Train clinicians to navigate ASD–PD overlap.
   Ongoing supervision and professional development support diagnostic precision.
5. Use dimensional functioning measures.
   Tools like WHODAS 2.0 and LPFS help capture nuance beyond categorical diagnoses.

Triad Psych’s Commitment to Clinical Clarity

For two decades, Triad Psych has been committed to delivering developmentally informed, trauma-aware, and evidence-based mental-health assessment.

Accurate diagnosis changes lives.
It shapes treatment, self-understanding, and long-term wellbeing.

If you are a clinician seeking consultation, a client seeking clarity, or a family member trying to understand complex diagnostic histories—we’re here to help.