How are personality disorders different from clinical syndromes? I have tried to sum up some general, historical assumptions on this issue.
People with personality disorders can be seen as extremes on a continuum, whereas people without a personality disorder represent the middle of a continuum. This
distribution is the so-called normal distribution, also called the bell curve.
In other words, all people have personality traits that differ, however, some people have developed traits in a dysfunctional manner (for different reasons). The development of dysfunctional and very deviant traits is linked to personality disorders.
For example, people who sometimes tend to be aggressive will not be considered as having a personality disorder, but people who are extremely aggressive are seen as antisocial.
In the American Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), this distinction is referred to as Axis I disorders (clinical syndromes) and Axis II disorders (personality disorders). This diagnostic system creates a common understanding of the underlying pathology.
Please note: The new DSM, version 5, is nonaxial. You can read more about it here. This post was written before the publication of DSM-5, and it therefore sums up some historical viewpoints. The section below is inspired by Kendell (2002).
It is common that personality disorders have an early onset, whereas clinical syndromes typically have a later onset.
In The International Classification of Diseases (ICD-10), personalets disorders are described as:
“Deeply ingrained and enduring behaviour patterns, manifesting themselves as inflexible responses to a broad range of personal and social situations.”
Unlike clinical syndromes, personality disorders have a life-long pattern. People with personality disorders are more likely to develop a number of clinical syndromes, such as depression, anxiety, and misuse disorder.
Furthermore, the symptoms of clinical syndromes are increased with the comorbidity of a personality disorder, and for this reason, they can be seen as risk factors for the development of clinical syndromes.
Clinical syndromes are thought to have a later onset than personality disorders, and both psychological and medical treatments are effective in the treatment of clinical syndromes in contrast to personality disorders, where the symptoms associated with the disorders are treated, and not the disorder itself.
Clinical syndromes have an underlying biomedical cause which the treatment can compensate for, whereas personality disorders are thought to underlie dysfunctional personality traits developed early in the life course. A biomedical cause is not (necessarily) considered to be involved in personality disorders.
That said, there are exceptions to the rule. For example, a growing body of evidence suggests that traumatic experiences in childhood can cause biomedical changes (Klaassens, 2010), which put people at risk for developing borderline personality disorder (Hodgdon, 1992).
So, the distinction between personality disorders and clinical syndromes is not always clear-cut because there are biomedical explanations for a number of personality disorders as well.
Serotonin, for example, is thought to underlie antisocial personality disorder, and there exists a large symptomatic overlap between avoidant personality disorder and the clinical syndrome, generalized social phobia.
Both DSM-IV and ICD-10 distinguish between personality disorders and clinical syndromes, but as it appears from this article, the distinction is not always clear-cut. For this reason, the new DSM-5 is nonaxial.