Psychopathy and narcissistic personality disorder are separate psychiatric disorders that have slightly overlapping symptoms. Sociopathy, however, is an older, outdated term for what is now called psychopathy.
Unfortunately, the differentiation of these widely-used terms has caused much confusion among the general public and mental health professionals alike. Part of the problem lies not in differentiating among individuals or disorders but in differentiating between labeling or classification systems. For example, narcissistic personality disorder is outlined in the Diagnostic and Statistical Manual of Mental Disorders (or DSM, first introduced in 1952 by the American Psychiatric Association, and currently in its fourth revised version, called the DSM-IV-TR), a classification system used in the United States and several other countries. According to the DSM-IV-TR, narcissistic personality disorder is characterized by a pattern of grandiose fantasies and behaviors, a need to be admired, and lack of empathy which begins early in life and persists throughout the lifespan in multiple areas of functioning. A person with this disorder may also have a strong sense of entitlement, may frequently take advantage of others, and may often be envious of others or believe that others are envious of him or her.
Psychopathy and sociopathy are not acknowledged as separate disorders in the current DSM, though the syndrome of psychopathy has been rigorously explored, defined, tested, and validated by researchers over the past several decades. Another consideration in differentiating these disorders is comorbidity, or the existence of two or more disorders at the same time in one individual—meaning that it is possible for one person to meet diagnostic criteria for both psychopathy and narcissistic personality disorder at the same time.
Understanding the difference between psychopathy and sociopathy really comes from an understanding of the different labels and conceptualizations historically used to describe psychopathy. Psychopathy, the disorder, has gone by many names. In 1801, it was called manie sans délire (“insanity without delirium”) by French physician and psychiatrist Philippe Pinel. In 1835, it was re-named moral insanity by British psychiatrist J. C. Prichard. In 1891, German psychiatrist J. L. Koch coined the term psychopathic inferiority (Koch chose the term “psychopathic”, which was actually a generic term for personality disorders until recent decades, to signify his belief that a physical basis existed for this condition—the term “inferiority” meant only that it represented an unfavorable deviation from the norm).
In 1952, the first edition of the DSM used the term sociopathic personality disturbance. This was the first official emergence of the term “sociopathy” to describe this condition, although this diagnosis was focused on internal psychological processes and personality traits (as opposed to more easily identified behaviors), which made it difficult for clinicians to diagnose properly. To address this shortfall, in 1980 the DSM-III introduced a more limited, behaviorally-based diagnosis called antisocial personality disorder which arguably lost many of the key personality-based symptoms of psychopathy that were found in earlier versions of the diagnosis.
As such, antisocial personality disorder and psychopathy are often confused, though they are not the same condition. Furthermore, though one prominent researcher (David Lykken) years ago proposed differentiating between sociopathy and psychopathy based upon causal factors (with psychopathy caused primarily by biological factors, and sociopathy due more to social factors such as improper or ineffective parenting), there has been no research that supports this theoretical speculation. In fact, there is no currently validated measure of sociopathy which would permit researchers to study whether it has different causes or properties than psychopathy. Thus, the current confusion between sociopathy and psychopathy may stem from an unwillingness of mental health professionals to discard an antiquated term, in spite of the extensive body of research developed on psychopathy but not sociopathy.