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Ask the Mental Health Expert Archives 2001-2004

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Undiagnosed Mental Illnesses

Q. What are some mental illnesses that are rarely diagnosed or go undiagnosed?

A. These are two separate, but related, questions. There are, of course, mental illnesses that truly seem to be rare birds, probably because they are just not highly prevalent in the population. One example might be delusional disorder. This consists of one or more non-bizarre delusions that persist for at least one month, unaccompanied by other classical features of schizophrenia, such as auditory hallucinations, disorganized thinking, inappropriate affect, etc. Although precise information about the population prevalence is lacking, the best estimate is that delusional disorder is present in only about 0.03% of the population (as per DSM-IV).

This would make it much rarer than, for example, schizophrenia (about a 1% prevalence) or bipolar disorder (about 1.5-2.5% lifetime prevalence). On the other hand, there are psychiatric disorders that are highly prevalent in the general population, but which are frequently missed or underdiagnosed in some clinical settings. For example, up to one in eight people in the U.S. may require treatment for clinical depression during their lifetimes. Yet only one-third to one-half of those with major depressive disorder are properly recognized and diagnosed by their health-care practitioners (See "Depression In Primary Care", U.S. Dept of Health & Human Services document 93-0550, 1993).

Similarly, only about one-third of those with bipolar disorder are in appropriate treatment, suggesting massive levels of mis-diagnosis or under-diagnosis. (In my own experience, bipolar disorder is frequently misdiagnosed as recurrent unipolar major depression). Controversies arise when we come to disorders such as Dissociative Identity Disorder (DID), formerly known as Multiple Personality Disorder.

You may know about this from movies, such as "The Three Faces of Eve." Some experts are convinced that DID is widely under-diagnosed, while others are adamant that this is a very rare disorder--and that in some cases, it is manufactured by gullible therapists interacting with highly suggestible patients. For more on this controversy, you may want to read the article by C.A. Ross in the American Journal of Psychotherapy 44:348-56, 1990.

September 2001

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