Co-occurrence of Personality Disorders with Other Disorders

In 1952, the American Psychiatric Association published the first Diagnostic and Statistical Manual of Mental Disorders (APA, 1952). The goal was to provide psychiatrists with a standardized set of definitions and descriptions of psychiatric diagnoses, as well as statistical information to facilitate diagnosis and further research. The intention was to unify the field, facilitate communication among clinicians, and to promote research in order to improve our understanding of mental illness and treatment. Over the subsequent decades, the DSM has undergone many revisions. Each successive revision reflected the level of technical knowledge available at that time. These revisions also reflected the prevailing view of mental illnesses held by the mental health profession and society at large. For a more detailed history of the various revisions of DSM please return to the section entitled, "The history of the current diagnostic system."

In 1980 the DSM III (APA, 1980) was published and the new multi-axial diagnostic system was unveiled, which is still in use today¹. The multi-axial diagnostic approach requires clinicians to record the results of their psychological evaluation on five different axes, or dimensions. Axis I and Axis II are where clinicians record their diagnostic findings, selecting from any of the disorders listed in DSM. The remaining three axes (Axis III, Axis IV, and Axis V) are not relevant to our discussion because they do not contain diagnostic information. Instead, these axes are used to identify relevant medical issues, record stressors in a person's life, and assess a person's level of functioning.

The first axis, Axis I, is used to record all psychiatric clinical disorders except for personality disorders and mental retardation² (intellectual disability). Axis I includes all major mental disorders, as well as developmental and learning disorders. The diagnostic categories of disorders included on Axis I are: Disorders of Children (such as learning and developmental disorders), Cognitive Disorders (such as dementia), Mood Disorders (such as Depressive or Bipolar Disorder), Anxiety Disorders, Substance-Related Disorders (such as alcoholism or drug abuse), Schizophrenia and other Psychotic Disorders, Somatoform Disorders, Sexual Disorders, Eating Disorders, Impulse Control Disorders, and Adjustment Disorders. In general, Axis I disorders are thought to represent acute problems or difficulties reflecting conditions that may come and go with the passage of time and/or treatment.

The second axis, Axis II, is reserved for the category of disorders called personality disorders and for mental retardation³ (intellectual disability). In contrast to Axis I acute diagnoses, Axis II disorders are thought to be pervasive and stable over time. In other words, the main distinction between Axis I and Axis II disorders is the stability of the condition being described across time. Axis II disorders are thought to be "always there" as a permanent part of the person. In contrast, Axis I disorders are believed to be illnesses that happen to a person and that come and go. For illustration purposes, it may be useful to consider the difference between Diabetes (a pervasive and chronic condition) and the Flu (an illness that comes and then goes away). If these were mental disorders, we might assign the Flu to Axis I (as it comes and goes), and assign Diabetes to Axis II, as it is always there (as it is a pervasive and chronic condition). The purpose of introducing a separate axis for personality disorders was to describe a person's underlying, lifelong, and pervasive characteristics so that they would not become overshadowed by the acute difficulties of the Axis I disorders.

Making the distinction between Axis I and Axis II disorders can be difficult at times. What complicates matters is that Axis I and Axis II disorders often occur together. This phenomenon of a person meeting criteria for several different diagnoses at the same time is called "co-occurrence of diagnoses." The Psychiatrist John Oldham and his colleagues published a study in 1995 in which they found high co-occurrence of essentially all major Axis I and Axis II disorders, and also high co-occurrence among the Axis II disorders (Oldham et al., 1995). Another psychiatrist, Robert Cloninger, points out in his introductory chapter to the book, Personality Disorders- Towards the DSM V, that nearly every personality disorder on Axis II can be reliably paired with at least one Axis I disorder (Cloninger, 2007). For instance, you may recall that Avoidant Personality Disorder (diagnosed on Axis II) is characterized by a profound sense of inferiority which leads to the avoidance of social situations for fear of embarrassment or humiliation. It is not difficult to see how this same person could meet the criteria for Social Phobia, an Axis I Anxiety Disorder. Let's look at some of these commonly co-occurring diagnoses a little more closely.

1 The multi-axial diagnostic currently in use may be modified in the upcoming DSM-V. However, many of the problems of co-occurrence between and among various psychiatric diagnoses are likely to remain until further research resolves the problems identified in this section. Further information about DSM-V is available at http://www.dsm5.org/pages/default.aspx and http://en.wikipedia.org/wiki/DSM-V.

2 The DSM-IV-TR (APA, 2000) uses the label mental retardation. However, the contemporary terminology is intellectual disability. It is anticipated that DSM-V will adopt the term "intellectual disability." Further information about DSM-V is available at http://www.dsm5.org/pages/default.aspx and http://en.wikipedia.org/wiki/DSM-V.

3 The DSM-IV-TR (APA, 2000) uses the label mental retardation. However, the contemporary terminology is intellectual disability. It is anticipated that DSM-V will adopt the term "intellectual disability." Further information about DSM-V is available at http://www.dsm5.org/pages/default.aspx and http://en.wikipedia.org/wiki/DSM-V.