Sadistic personality disorder

Sadistic personality disorder is a personality disorder involving sadomasochism which appeared in an appendix of the "Diagnostic and Statistical Manual of Mental Disorders" (DSM-III-R). The later versions of the DSM (DSM-IV, DSM-IV-TR and DSM-5) do not include it.
The words "sadism" and "sadist" are derived from Marquis de Sade.
Definition.
Sadism involves deriving pleasure through others undergoing discomfort or pain. The opponent-process theory is one way to help explain how an individual may come to not only display, but also enjoy committing sadistic acts. Individuals possessing sadistic personalities tend to display recurrent aggression and cruel behavior. Sadism can also include the use of emotional cruelty, purposefully manipulating others through the use of fear, and a preoccupation with violence.
Theodore Millon claimed there were four subtypes of sadism, which he termed "enforcing sadism", "explosive sadism", "spineless sadism", and "tyrannical sadism".
Comorbidity with other personality disorders.
Sadistic personality disorder has been found to occur frequently in unison with other personality disorders. Studies have also found that sadistic personality disorder is the personality disorder with the highest level of comorbidity to other types of psychopathological disorders. In contrast, sadism has also been found in patients who do not display any or other forms of psychopathic disorders. One personality disorder that is often found to occur alongside sadistic personality disorder is conduct disorder, not an adult disorder but one of childhood and adolescence. Studies have found other types of illnesses, such as alcoholism, to have a high rate of comorbidity with sadistic personality disorder.
Researchers have had some level of difficulty distinguishing sadistic personality disorder from other forms of personality disorders due to its high level of comorbidity with other disorders.
Removal from the DSM.
Numerous theorists and clinicians introduced sadistic personality disorder to the DSM in 1987 and it was placed in the DSM-III-R as a way to facilitate further systematic clinical study and research. It was proposed to be included because of adults who possessed sadistic personality traits but were not being labeled, even though their victims were being labeled with a self-defeating personality disorder. Theorists like Theodore Millon wanted to generate further study on SPD, and so proposed it to the DSM-IV Personality Disorder Work Group, who rejected it. Millon 
writes that "Physically abusive, sadistic personalities are most often male, and it was felt that any such diagnosis might have the paradoxical effect of legally excusing cruel behavior."
Sub-clinical sadism in personality psychology.
There is renewed interest in studying sadism as a personality trait. Sadism joins with subclinical psychopathy, narcissism, and Machiavellianism to form the so-called "dark tetrad" of personality.