The ensuing debate exposed a basic truth about the entire category: Personality disorders are not mental illnesses in the way that depression and schizophrenia are, for example. Mental illnesses are conditions of the mind, fundamentally disrupting a person’s inner thoughts and feelings, and usually have a biological origin. Brain scans can discern physical changes often associated with mental illnesses. Medication can treat them in many cases.

By contrast, personality disorders are not amenable to drug therapy. Nor have neuroscientists found any obvious biological underpinning or any gene associated with them. There also are no physical tests for a diagnosis.

Clinical psychologists and psychiatrists had long used a checklist approach. The fourth edition of the diagnostic manual listed nine common traits for narcissistic personality disorder, including “a grandiose sense of self-importance” and “requires excessive admiration” and “lacks empathy.” Generally, a person demonstrating at least five of those traits could be diagnosed with the disorder.

In 2010, some experts felt that too many of those markers overlapped with the traits seen in other personality disorders. Another objection: There were just so many narcissists in American society that labeling the condition as a disorder made no sense, they said.