Doctors and therapists have been trained to believe that DID (multiplicity) is very rare. They have also been trained that “when you hear hoof beats, look for horses, not zebras.” In other words, look first for the most common explanation of a set of symptoms. Once you have ruled out common diseases or conditions, start looking for the rarer ones. That’s common sense, but multiples are hardly zebras — they are far too numerous.
In the past, the most common misdiagnosis of multiplicity was schizophrenia. Why? Because both multiples and schizophrenics often hear voices. For multiples, it’s the voices of their alters or an auditory memory and the voices are usually heard inside the head. For schizophrenics, it’s auditory hallucinations and the voices usually seem to come from outside the head. This is not a hard and fast rule, because multiples sometimes hear the voices of their alters outside themselves, but it’s a good guideline.
Other things besides hallucinations – autism, flat affect and loose associations – characterize schizophrenia and are not commonly associated with multiplicity (except if one particular alter has been made to be schizophrenic.) Autism in this context means extreme self-absorption, an inability to take other people into account, or not using words in the way other people do. Flat affect means that emotions are toned down to the point of seeming non-existent a lot of the time. And loose associations means being all over the place in one’s speech; rhyming, making up words, jumping from one thing to another. A description slang term is “word salad.”
Multiples are not misdiagnosed as schizophrenic as often these days, but it still happens. I believe that, today, the more common misdiagnoses are bipolar disorder, cyclothymic disorder (rapidly cycling mood changes), and borderline personality disorder. This is just my opinion and is not based on studies that I have read.
In this case, the therapist is not focusing on whether the client hears voices or not, but on mood changes. The main characteristic of bipolar and cyclothymic disorders is mood swings from elation, often to the point of mania, to depression. In borderline personality disorder, the mood changes are secondary to changes in perception and/or beliefs. Another person may be seen as all-good for a while and then suddenly seen as all-bad, with the emotions changing accordingly. (Look for a blog entry on borderlines on July, 2011.)
If somebody has DID, mood changes can be traced to switching alters. Naturally, alters have different moods. Some are even created to ”hold” one emotion or another. Those that experienced the abuse tend to be depressed, hopeless, grieving, while those that dealt with the non-abusive world are more competent, social, and optimistic. So it makes sense that therapists, if they missed the multiplicity, would make these mood-based diagnoses.
PS. Andreas Laddis published “Dissociation and Psychosis in Dissociative Identity Disorder and Schizophrenia” in the Journal of Trauma and Dissociation, Vol. 13 No. 4, pp.397-413. I don’t have a citation for mood disorders and dissociation.