The Forgotten Personality Disorders

When you think about personality disorders, it’s likely that borderline and antisocial come to mind. These are, after all, the more flamboyant, and the ones most likely to be depicted in the media, arts, and literature. The DSM-5-TR, the American psychiatric diagnostic system, places these disorders in the so-called “Cluster A” of the more “odd, eccentric, and suspicious,” compared to the “Cluster B,” labeled “dramatic, erratic, and emotional,” into which borderline and antisocial fall.

Personality disorder researchers increasingly have come to challenge the idea that these complex patterns of behavior and qualities can be neatly placed into categories, much less clusters. Indeed, distinguishing between “eccentric” and “erratic” may seem a bit of an arcane distinction to you. The Alternative Model of Personality Disorders (AMPD) proposes instead that dimensions, not categories, should be used as the basis for diagnosis but it has not yet made it to the DSM classification system.

Setting this issue aside for the moment, and thinking back on Cluster A disorders, in some ways, they represent casualties of the current diagnostic system. Because Cluster B takes up so much of the oxygen in the room, less attention tends to be given to the treatment prospects for people with these other adaptational challenges. However, new research suggests that intervention can help people with these under-the-radar disorders.

What is Cluster A?

Before turning to the results of the intervention research, it can be helpful to summarize briefly the origins and qualities of the Cluster A disorders. As you can infer from their names, they seem schizophrenia-adjacent and, indeed, that’s how they were originally conceptualized. Unlike schizophrenia itself, however, the symptoms of these disorders don’t include delusions, hallucinations, or other hallmarks of what tend to be called “psychotic” disorders. Instead, the symptoms represent longstanding qualities such as distrust, suspiciousness, eccentricity, detachment, and a tendency to be uncomfortable in social situations. Unfortunately, though, the eccentricity and sometimes odd ideas of people in Cluster A mean that researchers place them more into the schizophrenia “spectrum” and less like personality disorders.

St. John University of Rome’s Simone Cheli and her international colleagues (2025) note that these challenges in figuring out what to do with Cluster A disorders have created some diagnostic confusion, including a less-than-ideal understanding of their prevalence. However, summarizing what is known about them, they note that: “All authors agree that Cluster A is associated with a severe, enduring, and pervasive impairment in psychosocial functioning and a risk for transitioning to psychosis” (p. 2).

Here, now, are the specific diagnostic features of each disorder:

Schizotypal personality disorders (SPD): eccentricity and social discomfort (this is the most reliable diagnosis)

Schizoid personality disorder (SZPD): emotional and social detachment

Paranoid personality disorder (PPD): suspiciousness and distrust

In reading these quick descriptions, it’s worth remembering that, in order to receive an actual diagnosis, individuals must demonstrate these patterns consistently over time and be impaired, as a result, in their ability to adapt to everyday adult life.

Treating Cluster A Disorders: The Evidence

Two questions guided the St. Johns U.-led research team: 1. Will people with these disorders remain in treatment and 2. Do the treatments work? Illustrating the relatively neglected nature of these disorders in the intervention literature, despite finding an initial set of 4,224 potential studies, the authors were only able to procure 7 meeting the empirical criteria for inclusion in the review. All were randomized controlled studies (RCT), meaning that they met the requirements of involving random assignment to matched treatment vs. control groups. However, the number became whittled down further to five after removing those whose measurement methods were too inconsistent to use. Of the five, four included pharmacotherapy and only one involved a strictly psychosocial intervention.

These data alone show just how overlooked these disorders are in the clinical literature. There are hundreds, if not thousands, of well-controlled studies on the Cluster B disorders.

Limitations aside, the results provided convincing evidence that, not only did people with these disorders stick with the treatments, but that their symptoms were alleviated and their overall general functioning improved. As the authors concluded: “Our results suggest that the level of feasibility and safety of treatments for Cluster A PDs are similar to those for all other PDs” (p. 12).

Turning to the individual studies, the psychotherapy-alone study was actually conducted by part of the author team for the review (Cheli et al., 2023). Across a 10-month period, the individuals in this study received two types of psychotherapy. The first, with the acronym MERIT (Metacognitive Reflection and Insight Therapy), involves focusing on a set of elements that include reflection about the self and others and stimulation of mastery. The second component was CFT (Compassion-Focused Therapy) and includes achieving a soothing breathing rhythm, developing self-compassion, accepting difficult emotions, and compassion for suffering others.

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As you can see from this description, these approaches tackle directly some of the core aspects of Cluster A symptoms. The key, in the words of the authors, was that “both MERIT and CFT have a specific focus on the intersubjective experience and use intervention to support clients by fostering their understating of self and others and achieving a sense of social safeness.” By the end of therapy, patients in the study no longer met the diagnostic criteria for the disorder.

What Made the Treatments Work?

Although the final set of studies in the 2025 meta-analysis was small, the work of the Italian group is important in bringing to light not only the nature of Cluster A disorders, but also their amenability to treatment. Additionally, focusing on social cognition with the intervention using mentalization, compassion, and relaxation directly ties into the core features of these disorders.

These findings also show the benefit of looking at personality disorders not as categorical entities but as disturbances in specific psychological processes, especially when you think about the inner experience of people who show these symptoms. Does it matter to them whether there’s a “letter” in their diagnositic category? is it more important in their daily lives that they find it difficult to relate to others and may have developed some unusual ideas about the way the world works? Chances are, if they could gain the kind of insight that MERIT and CFT can provide, they’d just as soon take advantage of these opportunities to turn their lives around.

To sum up, just because a personality disorder attracts a lot of attention doesn’t mean that it’s the only one worth studying. Helping people whose long-term adaptation has become a challenge ultimately is what can make psychological intervention have significant effects on their lives, regardless of whether they fit neatly into an A, a B, or a C.

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