When asking differential questions about multiple personality disorders, it is important to understand why you are asking the question and how you intend to use the information. Without this perspective and focus, the data may be overwhelming, confusing and misleading. For example...
~ if your child is not responding to therapy, it makes sense to look more carefully into the possibility that the wrong personality disorder was diagnosed or whether there are comorbid (multiple) personality disorders at play.
~ If you are trying to get along better with your wife, it's not as important to pinpoint the specific disorder or analyze the comorbidity as it is to recognize and fully understand the problem behaviors and how to constructively deal with them.
~ If you are recovering from a failed relationship, the important thing is often to understand which behaviors were pathologic (mental illness) and which were just the normal run of the mill problems common to failing/failed relationships - there is often a bias to assign too much to the "pathology" and not enough to common relationship problems, or the issues we created by our own behaviors.
It's important to know that the distinctions are not all that neat and tidy. In a 2008 study, comorbidity with another personality disorder was very high at
74% (77% for men, 72% for women). This is one reason why there is controversy around the DSM classifications of Personality Disorders - there is so much overlap it is confusing even to professionals - personality disorders are real, but they are not easily or neatly defined.
Comorbid w/BPD-------------- Paranoid Schizoid Schizotypal Antisocial Histrionic Narcissistic Avoidant Dependent OCD More info | Men----------- 17% 11% 39% 19% 10% 47% 11% 2% 22% | Women------- 25% 14% 35% 9% 10% 32% 16% 4% 24% |
Some helpful hints for sorting through this.
- General and Specific There are definitions for "personality disorder" as a category and then there are definitions for the subcategories (i.e., borderline, narcissistic, antisocial, etc.). Start with the broader definition first. Keep in mind that to be a personality disorder, symptoms have been present for an extended period of time, are inflexible and pervasive, and are not a result of alcohol or drugs or another psychiatric disorder - - the history of symptoms can be traced back to adolescence or at least early adulthood - - the symptoms have caused and continue to cause significant distress or negative consequences in different aspects of the person's life. Symptoms are seen in at least two of the following areas: thoughts (ways of looking at the world, thinking about self or others, and interacting), emotions (appropriateness, intensity, and range of emotional functioning), interpersonal functioning (relationships and interpersonal skills), or impulse control
- Spectrum Disorders An extremely important aspect of understanding mental disorders is understanding that there is a spectrum of severity. A spectrum is comprised of relatively "severe" mental disorders as well as relatively "mild and nonclinical deficits". Some people with BPD traits cannot work, are hospitalized or incarcerated, and even kill themselves. On the other hand, some fall below the threshold for clinical diagnosis and are simply very immature and self centered and difficult in intimate relationships.
- Comorbidity Borderline patients often present for evaluation or treatment with one or more comorbid axis I disorders (e.g.,depression, anxiety disorders, bipolar disorder, ADHD, autism spectrum disorders, anorexia nervosa, bulimia nervosa). It is not unusual for symptoms of these other disorders to mask the underlying borderline psychopathology, impeding accurate diagnosis and making treatment planning difficult. In some cases, it isn’t until treatment for other disorders fails that BPD is diagnosed. Complicating this, additional axis I disorders may also develop over time. Because of the frequency with which these clinically difficult situations occur, a substantial amount of research concerning the axis I comorbidity of borderline personality disorder has been conducted. A lot is based on small sample sizes so the numbers vary. Be careful to look at the sample in any study -- comorbidity rates can differ significantly depending on whether the study population is treatment seeking individuals or random individuals in the community. Also be aware that comorbidity rates are generally lower in less severe cases of borderline personality disorder.
- Multi-axial Diagnosis In the DSM-IV-TR system, technically, an individual should be diagnosed on all five different domains, or "axes." The clinician looks across a large number of afflictions and tries to find the best fit. Using a single axis approach, which we often do as laymen, can be misleading -- looking at 1 or 2 metal illness and saying "that's it" -- if you look at 20 of these things, you may find yourself saying "thats it" a lot.
A note in the DSM-IV-TR states that appropriate use of the diagnostic criteria is said to require extensive clinical training, and its contents “cannot simply be applied in a cookbook fashion”.
- Don't become an Amateur Psychologist or Neurosurgeon While awareness is a very good thing, if one suspects a mental disorder in the family it is best to see a mental health professional for an informed opinion and for some direction - even more so if you are emotionally distressed yourself and not at the top of your game.
I hope this helps keep it in perspective.

Skippy
DIFFERENCES|COMORBIDITY: Overview of ComorbidityAdditional discussions...
Personality Disorders Borderline and Paranoid Personality Disorder Borderline and
Schzoid/Schizotypal Personality Disorder Borderline and Antisocial Personality DisorderBorderline and Histrionic Personality DisorderBorderline and Narcissistic Personality DisorderBorderline and Avoidant Personality DisorderBorderline and
Dependent Personality Disorder Borderline and Obsessive Compulsive Personality Disorder Borderline and
Depressive Personality Disorder Borderline and
Passive Aggressive Personality Disorder Borderline and
Sadistic Personality Disorder Borderline and
Self Defeating Personality Disorder Other Borderline PD and Alcohol DependenceBorderline PD and AspergersBorderline PD and Attention Deficit Hyperactivity DisorderBorderline PD and BiPolar DisorderBorderline PD and Dissociative Identity DisorderBorderline PD and P.T.S.D.Borderline PD and Reactive Attachment Disorder (RAD)