I've been deeply impressed by Judith Herman's book Trauma and Recovery, which claims that normal responses to trauma can mimic any number of mental illnesses. Referring to adult survivors of childhood abuse and neglect, she explains that sometimes, trauma survivors carry into adulthood an extraordinary capacity to dissociate, shut down feelings, and go numb--responses that served them well while they were being abused or neglected but that are disastrous in adult relationships. These symptoms--along with a pattern of intense, short-lived relationships--frequently result in a diagnosis of "borderline personality disorder" or even "multiple personality disorder."
At some point, Herman says, the defensive structures built in childhood by abused or neglected children can break down. When the defensive structures break down, the personality DIS-integrates, and the result, according to Herman, is misdiagnosis: "When and if a breakdown occurs, it can take symptomatic forms that mimic virtually every category of psychiatric disorder. "
This led me to thinking about the whole enterprise of diagnosis, a process that one psychiatrist I know considers "more of an art than a science." With mental illness, for which there are no blood tests or brain scans, diagnosis--the act of naming a set of symptoms--is an entirely verbal and sociocultural act. It's interesting that we use a non-physical, immaterial diagnostic process to name illnesses that are increasingly considered to be physical/genetic/biochemical in nature. I am surprised that more people don't feel skeptical about the obvious paradox in this situation.
This paradox certainly explains why career mental health patients, unlike patients with diabetes, often receive several different diagnoses over the course of their lifetimes. The same set of symptoms, depending on who's looking, could viably be called multiple personality disorder, borderline personality disorder, complex post-traumatic stress disorder, or even garden variety codependency (although the last two are not in the DSM-IV, so no one in a hospital would receive these diagnoses). It reminds me of the particle/wave paradox in physics: in certain experiments, light acts like a wave; in other experiments, light acts like particles. So is light a wave or a bunch of particles? We are uncertain. Maybe light. Maybe wave. Maybe both.
Considering the verbal/sociocultural basis of the diagnostic process with mental disturbances, it would seem advisable to approach diagnosis with the same humility and openness practiced by quantum physicists. Maybe it's this. Maybe it's that. Maybe it's both. Depends on who's looking and what tools they are using to observe. Maybe we just don't know exactly . . .