Are mental illnesses diseases?

I’ll always remember reading the Amazon reviews for the most recent version of the DSM-5. (For those who don’t know, the DSM-5 the handbook that mental health professionals in the United States use to describe and characterize all forms of mental illnesses.) Not surprisingly, many of the early reviews were not flattering–the science of psychiatry is still very young, and the DSM has always been better at categorizing symptoms than describing discrete disorders. But one line of criticism stuck out to me: the accusation that the DSM was describing normal human experience as diseases.

Now I’ll admit, on strictly philosophical grounds, describing a mental illness as a disease can be problematic. By some standards, a “disease” needs to involve an observable physiological process. For example, lupus qualifies as a disease because there are inflammatory markers that can be detected in the blood. Alzheimer’s dementia is a disease because there are characteristic brain changes that you can be detected when the brain is biopsied (although this is never done in a living patient). But for depression, schizophrenia, and almost all other DSM diagnoses, we really don’t have biological markers that adequately describe these disorders. This doesn’t mean they don’t have a biological basis. It just means that the diagnostic tools we use are still very limited. In deference to this distinction, the words “illness” and “disorder” are more commonly used than the word “disease” when used to describe psychopathology.

Some people will say that mental illnesses are not diseases, illnesses, or disorders because these words can be stigmatizing. I agree that putting a label on a person’s experience may be burdensome. I prefer to let people define their experience in their own words. The spectrum of symptoms associated with any DSM-defined diagnosis is immense, and how a person relates to their symptoms is very personal. However, I do believe that it is important for clinicians to use accurate terminology within the private medical record so that appropriate communication can occur between providers. But I would never suggest that a particular diagnosis defines who a person is or what he or she may achieve in life.

From a clinical perspective, DSM-diagnoses are defined as illnesses and disorders not because of their symptoms, but because of the impairment that people with them experience. This is an important distinction because people have widely divergent personalities, behaviors, and habits–and diversity alone is not a sign of illness. Impairment is usually defined as disruption of the person’s normal ability to function at work, school, or in relationships. However, impairment can also occur when symptoms cause a person to experience great personal distress. People are wonderfully diverse and incredibly adaptive and it just doesn’t make sense to describe symptoms as an illness if they don’t cause impairment.

Regardless of what we call these symptoms, I hope we can all agree that providing treatment to people in need should be an important priority.

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