Is DID a personality or thought disorder?

Q: I've seen news articles referring to MPD as either a thought disorder or a personality disorder. What is it? - Anon

A: Multiple Personality Disorder seems like it would fall under the category of a "personality disorder" because of the name, but it is not. Rather, it is grouped with other disorders under a subtype called "dissociative disorders", which fits the newer name Dissociative Identity Disorder. It is also not classified as a "thought disorder".

The handbook used to diagnose mental health issues is called the Diagnostic and Statistical Manual of Mental Disorders (DSM).

There are five axis in a diagnosis:
- Axis I: Clinical Disorders (mental illnesses, substance abuse, etc.) including developmental and learning disorders
- Axis II: Personality Disorder and Mental Retardation
- Axis III: Medical conditions and physical disorders (such as brain injury/post-concussive syndrome, menopause, chronic pain, etc.)
- Axis IV: Psychosocial and environmental/support system stressors contributing to the disorder/symptoms (typically issues that are making things worse psychologically or could be barriers to recovery)
- Axis V: Global Assessment of Functioning (a rating scale on 0 - 100 of how well the person is functioning in interpersonal, vocational, and self-care areas)

Thought disorders are usually symptoms of an Axis I disorder, typically in the Schizophrenia-type disorders and Autism. Read here for more about common thought disorders such as pressured speech, tangential speech, word salad, and echolalia.

Personality disorders are pervasive (they happen in relation to most situations/people) and enduring (life-long) patterns of thinking, reacting, and interacting with others. Common examples include antisocial, borderline, schizoid, narcissistic, and dependent.

Dissociative Identity Disorder is an Axis I diagnosis as part of the subgroup called Dissociative Disorders (which includes DID, fugue, depersonalization, and dissociative amnesia).

It is possible for specific alters to have characteristics of a thought disorder or personality disorder. Some people may be diagnosed with MPD/DID and borderline personality disorder, but this would not be clinically appropriate if only a few of the alters have borderline characteristics because it would fail to meet the full criteria of pervasive and long-term.