Yes and No
Yes, both are listed as the same illness in the APA diagnostic manual known as the DSM-5 and both are typically used interchangeably with one another.
No, Conversion Disorder [CD] and Functional Neurological Disorder [FND] are theoretically different concepts. CD is the theory that symptoms are the result of suppressed psychological trauma converting to physical symptoms. Studies have found many do not have a history of major emotional traumatic events, or major depression/anxiety. Even if a patient does have mental health issues, now or in their past, there is no quantifiable way to confirm a correlation to symptoms. The change in criterion now makes it easier for physicians to use the CD/FND diagnosis, where in the past they couldn’t when they found their patient did not meet the criterion standard and there was no “converting” of symptoms taking place. Because there is sometimes no identifiable mental health issues, the need to identify one was removed. However, there are some patients who do identify with the Conversion Disorder theory.
We advocate that patients receive respectable and equal care based on their needs.