Writers' characters, muse, voices Vs. alternate personalities of persons with multiple personality: Are there any differences in the phenomena?

The obvious difference is that the writer’s characters, muse, and voices are involved in writing, professionally; whereas, the alternate personalities of most persons with multiple personality are not involved in writing, professionally.

But are there any essential differences in the phenomena? If you can think of any, please submit your comments.

Other psychological conditions that have been studied in regard to writers—principally, major depression and bipolar disorder—make no sense. Major depression and mania would prevent or impair, not facilitate, professional writing. And there is nothing about depression or mania that looks like a writer’s characters or muse. Moreover, any correlation between major depression or bipolar disorder and writing is probably because, like multiple personality, they are more common in people who have had a traumatic childhood. 

Why haven’t other psychiatrists and psychologists seen the connection between writing and multiple personality? Partly because most of them have not had clinical experience with both bipolar disorder and multiple personality (some academics may have seen neither). Partly because they have not studied what writers say about themselves or studied the novels. But mostly because they have not considered the possibility that multiple personality has a nonclinical, high-functioning version.