No diagnostic system can be perfectly constructed. Therefore, it should come as no surprise that the current DSM-5 (APA, 2013) diagnostic system for personality disorders has its fair share of problems. Researchers and clinicians have identified several, significant, diagnostic difficulties that can be summarized as follows:
1. The DSM-5 method for diagnosing personality disorders is called a categorical approach. However, an alternative method, called the dimensional approach, is also presented in DSM-5 for consideration and future research. There have been numerous problems with the categorical method that the dimensional approach attempts to resolve.
2. The DSM does not account for the relative importance of various symptoms, and the descriptions of symptom criteria are overly broad. This means that patients diagnosed with the same disorder may have very dissimilar clinical presentations.
3. There is a high degree of overlap or co-occurrence of personality disorders with each other, and other mental disorders.
4. Each of these difficulties will be further discussed in the following sections.
1. A categorical versus dimensional approach to personality diagnosis:
The DSM-5 (APA, 2013) includes two types of diagnostic models for personality disorders. The first type is called a categorical model. This is the "official" diagnostic method listed in the section called, Diagnostic Criteria and Codes. However, an alternative dimensional model is also presented in DSM-5 for future consideration. This alternative dimensional model is described in the DSM-5 chapter called Emerging Measures and Models.
Let's review and contrast these two different diagnostic methods. The current and "official" diagnostic method derives from a categorical model of disease, disorders, and conditions. In this model, you either have a disorder, or you do not. Pregnancy is one such condition. You either are pregnant or you are not. You cannot be a little bit pregnant. It's much like the traditional light switch. It is either on, or it is off. For some conditions, such as pregnancy, a categorical model is very suitable.
In contrast, a dimensional model allows for varying degrees of impairment or severity. The dimensional model is more like a light switch on a dimmer. It has a range from being completely off, to somewhat on/off, to completely on. This model is more suited for conditions where there is a continuum ranging from healthy to unhealthy. Unlike pregnancy which is an absolute condition, we cannot say you either have a personality or you do not. Everyone has a personality. Therefore, it is more accurate to consider personality on a continuum ranging from very healthy to very unhealthy/impaired.
As we previously mentioned, personality disorders are somewhat dissimilar to other types of psychiatric conditions. This is because while everyone has a personality of some sort or another, not everyone has depression, anxiety, schizophrenia, etc. Those disorders lend themselves to a categorical approach to diagnosis. In contrast, a dimensional model may be more suitable for personality disorders because personalities can range from healthy to disordered/impaired. The categorical model assumes each personality disorder is a separate and distinct category; i.e., separate from other personality disorders, and distinct from "normal" personalities. In contrast, the dimensional model views various personality features along several continuous dimensions (or continuums). In this dimensional approach, personality disorders would represent the extremes along a continuum of otherwise normal, healthy personality dimensions.
The benefit of a dimensional approach can be illustrated by contrasting two people; one who has a Narcissistic Personality Disorder and one who does not. The Narcissistic Personality Disorder is characterized by rather extreme forms of self-centeredness and grandiosity. However, even ordinary, healthy people will sometimes act in ways that are self-centered and grandiose. Though the dimension of self-centeredness is the same, the difference is in the extremity of expression. People with Narcissistic Personality Disorder behave in a self-centered manner most all the time, while people without this disorder behave this way only some of the time. In this case, it makes sense to talk about a continuum or dimension of self-centeredness, which varies from low to high. Thus, we can use this dimension of self-centeredness to distinguish between people with Narcissistic Personality Disorder from those without this disorder, by plotting their degree of self-centeredness along this dimension.
While we may gain greater accuracy and precision when we view personality disorders as dimensional or continuous in nature, we lose a large degree of diagnostic simplicity. With a dimensional approach, everything becomes more complicated. How many dimensions are important to take into account? Is it possible to establish a "cut off" on relevant dimensions beyond which we can say a particular disorder is present? For instance, just how self-centered do you need to be in order to reach the level of a Narcissistic Personality Disorder?