I stumbled upon this article from the American Psychological Association "A broader view of psychopathy" while looking for a quick legitimate source for psychopathy being a personality disorder and it had a wealth of interesting information including the origin of psychopathy being part of ASPD:
For these and other reasons, the mental health community has not had an easy time homing in on a uniform definition of psychopathy. For decades, its symptoms were examined in two very different populations: people in criminal or forensic settings and people in inpatient or community mental health settings. These groups had somewhat different characteristics, which led to different ways of conceptualizing and assessing psychopathy, said Florida State University psychologist Chris Patrick, PhD, who studies and has written extensively on the condition.
To add to the complexity, psychopathy is not a diagnostic category in the Diagnostic and Statistical Manual of Mental Disorders (DSM-V)—one reason the area tends to be both underfunded and undertreated, Marsh added. In part, that is due to earlier disagreements in the field: Some of those studying the disorder worried that a psychopathy diagnosis would stigmatize people too much, while others were concerned that clinicians would have difficulty in accurately assessing traits like callousness or cruel or indifferent disregard of others. So, although psychopathy was included in the first two editions of the DSM, it was replaced in the third edition by antisocial personality disorder (ASPD), which focuses mainly on the behavioral aspects of psychopathy, such as aggression, impulsivity, and violations of others’ rights, but only minimally on personality characteristics like callousness, remorselessness, and narcissism. As a result, only about a third of those diagnosed with ASPD also meet the criteria for psychopathy, according to research using validated scales, which often leads to confusion over how and if the two conditions are related, Marsh noted.
And regarding successful treatment, including schema therapy:
Collectively, these findings suggest that those with or at risk for psychopathy need more than single-dose therapy. Rather, therapy needs to be both correctly tailored to the problems the person is facing and of sufficiently long duration to ensure that changes stick, Viding said.
