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Overlaps, prevalence and comorbidity
Overlapping symptoms
It is now recognised that ASD and personality disorders (PDs) have a variety of factors in common. However, the exact nature of the relationship between ASD and the PDs remains unclear. Differentiating between ASD in adolescence and adulthood and PDs can often be challenging due to the similarity in symptomatology. For instance:
- PDs belonging to cluster A, such as schizoid or schizotypal, exhibit odd behaviours and social withdrawal, which are also observed in high-functioning ASD (Level 1/ Asperger syndrome) individuals.
- Similarly, cluster B PDs may display dysregulation in emotional expressivity, self-injurious behaviours (e.g., borderline PD – Bemmouna, Weiner 2023), and empathic behaviours (e.g., antisocial PD).
- Lastly, cluster C PDs may exhibit social avoidance (e.g., avoidant PD) or a need for sameness (e.g., obsessive-compulsive PD) (De Cagna et al. 2020).
Similar to HFA/AS, individuals with borderline PD have a strong drive to systemize, suggesting an overlap between borderline PD and ASC (Dudas et al. 2017).
Social cognition deficits (including Theory of Mind difficulties) are also associated with a number of other disorders, including borderline PD (Fonagy, Bateman 2008; Frick et al. 2012; Baez et al. 2015) and Schizotypal-Schizoid Personality Disorders (Booules-Katri et al. (2019).
Difficulties related to the social and relational fields are characteristics found in patients with borderline PD, as well as in individuals with HF autism (Vegni, D'Ardia, Torregiani 2021).
Both people with autism and borderline personality disorder are significantly challenged in terms of understanding and responding to emotions and in interpersonal functioning (Dudas 2017).
Deficits in social relationships and social interaction are present also in both HF ASD/AS and schizotypal PD (Stanfield et al. 2017). Prominent schizotypal traits in people with ASD may constitute an endophenotype coinciding with a particularly poor quality of life (Klang et al. 2022). There are also phenotypic similarities between high-functioning ASD and both schizoid/schizotypal and obsessive–compulsive PD (e.g., Keller et al. 2019).
On the other hand, subthreshold autism spectrum may be relevant for people with borderline PD (Dell'Osso, Cremone, Carpita 2018). A mounting body of literature is showing that, in the clinical and general population, ASD or autistic traits (ATs) would appear to be spread along a continuum, reaching the highest levels among borderline PD individuals. In borderline PD (and bipolar disorder), higher autistic traits were linked to suicidal tendencies, although with different patterns of association between borderline PD and bipolar disorder individuals (Dell’Osso, Cremone, Amatori et al. 2021; Dell'Osso, Cremone, Nardi 2023).
Notably, individuals with ASD (1/AS) who also exhibit PD traits may experience more severe impairment in adaptive functioning and greater challenges in daily life. The identification and understanding of this comorbidity are crucial for accurate diagnosis, tailored interventions, and improved treatment/support outcomes.
Comorbidity
Co-occurring mental health conditions are more prevalent in the autism population than in the general population (Lai et al. 2019) – from 70% of adults with HFA/AS (ASD 1) (Roy 2015) to 79% have at least one psychiatric comorbiditiy (Lever, Geurts 2016).
Late-diagnosed individuals show higher levels of co-occurring psychiatric conditions (Mattila et al. 2010).
There is evidence of an increased prevalence of co-existing ASD among those diagnosed with a personality disorder (such as, e.g., borderline, schizotypal and obsessive-compulsive personality disorders) (Gillett et al. 2022).
Comorbidities have a significant impact on individuals with ASD, and vice versa. It is important to recognize that autism can present differently when accompanied by a personality disorder compared to when it is not. Therefore, it is crucial to tailor the diagnosis and treatment/support approaches accordingly.
Prevalence of PD in ASD
People with autism and an intellectual disability are less likely to receive a diagnosis of PD (Ghaziuddin 2005; Tsakanikos et al. 2006).
68% ASD people (without intellectual/ learning disability) met the criteria for at least one PD, 40% had 2 PDs, 18% - 3 PDs: primarily obsessive–compulsive (40%), avoidant (29%), and schizoid PD (21%), paranoid (19%) and schizotypal (16%). Concerning cluster B PD, rates of comorbidity were low, but antisocial disorder was common in the pervasive developmental disorder subgroup. A high number of patients (40%) had more than two PDs, and 18% - more than 3 PDs. The prevalence of PD did not differ between genders, with the exception of schizoid PD, which was significantly more common among women. (Hofvander et al. 2009)
Cluster A and cluster C personality PDs are the most frequent co-occurring PDs in ASD: a study showed that 48% of a sample of young adults with AS fulfilled the criteria for a cluster A or cluster C PD diagnosis. (Lugnegård, Hallerbäck, Gillberg 2012).
Avoidant and schizotypal personality traits are more common in individuals with ASD compared to the control group (without ASD). Individuals with ASD scored higher on detachment and stress susceptibility and had a median of four PDs. More than 40% of the ASD group reached the cut-off score for avoidant, borderline and obsessive–compulsive PD, more than a third had depressive, schizotypal, schizoid and narcissistic PD and at least 25% reached the cut-off for paranoid and passive-aggressive PD. Females with ASD scored significantly higher than males on borderline and passive-aggressive traits (Rinaldi et al. 2021).
In individuals with comorbid ASD and borderline PD, the higher suicidality was observed. Despite similar levels of depression, people with both ASD and borderline PD have higher levels of suicidal ideation than those with either ASD or with borderline PD alone (Chabrol, Raynal 2018).
Challenges in diagnosis
Since differentiating between ASD and PD is such a complex task, it has been argued that there is a need for additional understanding and markers for facilitating diagnostic procedures. There is an urgent need to explore, first, how clinicians make diagnostic decisions and, second, how to effectively deal with the challenges and difficulties they face when making decisions. Also, where there are clear overlaps, how do clinicians choose how to attribute labels in order to understand the person (Allely, Woodhouse, Mukherjee 2023).
Differential diagnosis should be based on clinical examination and a very careful history investigation of the first years of development, the first social relationships with other children and adolescents, changes of lifestyle during development and clinical symptoms of ASD in the first years of life (Rinaldi et al. 2021).
When evaluating ASD in adulthood, it is crucial to consider the presence of PD for both differential diagnosis and effective treatment planning (De Cagna et al. 2020).
The first issue for clinicians evaluating personality in ASD patients is to determine whether personality traits are part of the same autistic phenomenology or rather represent different categorical factors (comorbidity).
Clinicians need to be aware of the potential comorbidity to ensure a comprehensive assessment and appropriate intervention strategies, but clinical assessments often omit screening for personality disorders (PDs), which are especially common in individuals with high-functioning ASD.
The accurate assessment and identification of a PD in an individual with an ASD opens the opportunity to provide more customised, ASD-informed treatment. Identification of an ASD in an individual with a PD can ensure that psychotherapeutic interventions are contextualised to a person's communication and social cognition (Carthy, Murphy 2021).
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