My understanding is that psychopathy is not considered to be a personality disorder in the DSM 5. A significant fraction of psychopaths will be diagnosed with ASPD but, although the overlap is high you can have a psychopath who is not ASPD and someone with ASPD who is not a psychopath.

My understanding is also that psychopathy is associated with pronounced alterations in brain development so it can be considered a neurological impairment that can be measured objectively.