Dissociative Identity Disorder

The Diagnosis of DID

To meet the criteria for a DSM-IV diagnosis of DID, two or more distinct identities must be present who recurrently take control of an individual's behavior. These alter identities may have distinct personal histories, names, and abilities (e.g., computer proficiency, literacy) and can even vary in professed sex and age. This fractionation of identity must also be accompanied by an inability to recall important personal information, beyond that of ordinary forgetfulness. This memory loss, termed inter-identity amnesia, is thought to result from the compartmentalization of memory within identities and can manifest in many ways, such as gaps in time or the discovery of unfamiliar items in one's possession.

The properties of inter-identity amnesia can vary. In a one-way amnesia, communication is asymmetrical, as one identity may be omniscient for the experiences of the other but not vice versa. In a two-way amnesia, both identities are unaware of each other's experiences, memories, and sometimes even existence. A diagnosis of DID cannot be made if the symptoms are due to substance use or a general medical condition. DID is diagnosed more commonly in females than males (from three to nine times more often) and is often diagnosed in individuals with a history of other psychiatric diagnoses. Symptom onset varies, although many individuals report dissociative symptoms dating back to as early as childhood.

As with most other diagnoses, clinicians rely on the self-report of patients when diagnosing DID. This is typically done using either unstructured questioning or a structured interview such as the Structured Clinical Interview for DSM-IV Dissociative Disorders (SCID–D). The Dissociative Experiences Scale (DES) is another common self-report measure of dissociative symptoms, which requires individuals to rate their symptoms on a Likert-type scale, although the DES cannot confirm the diagnosis of DID.

[Page 228]Given the centrality of amnesia to DID, evidence of inter-identity amnesia is essential to a diagnosis. Caution is warranted when interpreting self-reported symptoms of amnesia, however, as research using objective measures of memory reveals an inconsistent picture that does not consistently corroborate the subjective symptoms reported by patients. Studies that have examined memory transfer across identities have provided mixed results, typically finding that some memories are shared between reportedly amnesic identities while other memories are not. It has been proposed that these differences in memory transfer depend on whether the memories are explicit versus implicit. Explicit memory tests require conscious recollection and typically produce amnesia between identities. For example, an amnesic identity may deny any memory of words presented to another identity when asked to recall them. In contrast, implicit memory tasks rely on the premise that prior experiences can influence subsequent behavior independent of conscious awareness—such tasks often show memory transfer. Although the amnesic identity may claim to not recognize the words, given an implicit test, such as a word-stem completion task, he or she may perform in a manner that suggests memory of the words on some level, typically assumed to be implicit and unconscious.

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