The standard mental status exam's assessment of memory has a blind spot. It doesn't ask patients if they've had recurrent sober memory gaps (dissociative amnesia), which is often the only clue that a patient might have dissociative identity disorder (DID). It leaves it to patients to raise the issue.
Why don't undiagnosed DID patients bring up the subject of their memory gaps? First, they don't know its clinical significance (that these might be times that other identities were “out”). Second, they are generally unaware that they've lost time, except when something embarrassing, confusing, or disturbing confronts them with the fact, and they don't like to think about it. Third, they're afraid that telling people they have memory gaps—periods of time they don't remember and when they're not in control of their own behavior—might make people think they're“ crazy.”
Why do clinicians need a “clue” (memory gaps) to the presence of DID? What's the mystery? When DID is present, isn't it obvious? If you've ever seen an interview of a known DID patient, weren't the switches from one identity to another something you couldn't miss?
Actually, what you see in such an interview is the postdiagnosis picture, not how DID presents. Prediagnosis, alternate identities usually answer to the patient's regular name, because they prefer to remain incognito. They lose that reticence once diagnosis has blown their cover, but all that you would have found prediagnosis (if you had inquired) were memory gaps.
Once you discover that your patient does have a history of memory gaps, you can ask about these episodes. For example, after some gaps, a patient finds poems. She agrees that nobody else could have written these poems (which she found among her personal papers), but she doesn't remember writing them; they don't express her views, and they're not even in her handwriting.
Keeping the interview focused on these poems will eventually cause a switch to the identity who wrote them. You might ask this identity why she writes poems, her age, and her name. If you then turn the focus away from the poems, or simply address the patient by her regular name, you will prompt a switch back to the regular identity, who has amnesia (a memory gap) for your conversation with the poetry-writing identity.
The standard mental status exam does not now, but should, screen for memory gaps (dissociative amnesia). Otherwise, when it comes to diagnosing DID, the clinician will be clueless.
