Pathological narcissism is a life-long pattern of traits and behaviours which signify infatuation and obsession with one’s self to the exclusion of all others and the egotistic and ruthless pursuit of one’s gratification, dominance and ambition.
As distinct from healthy narcissism which we all possess, pathological narcissism is maladaptive, rigid, persisting, and causes significant distress, and functional impairment.
Pathological narcissism was first described in detail by Freud in his essay “On Narcissism” (1915). Other major contributors to the study of narcissism are: Melanie Klein, Karen Horney, Franz Kohut, Otto Kernberg, Theodore Millon, Elsa Roningstam, Gunderson, and Robert Hare.
What is Narcissistic Personality Disorder (NPD)?
The Narcissistic Personality Disorder (NPD) (formerly known as megalomania or, colloquially, as egotism) is a form of pathological narcissism. It is a Cluster B (dramatic, emotional, or erratic) personality disorder. Other Cluster B personality disorders are the Borderline Personality Disorder (BPD), the Antisocial Personality Disorder (APD), and the Histrionic Personality Disorder (HPD). The Narcissistic Personality Disorder (NPD) first appeared as a mental health diagnosis in the DSM III-TR (Diagnostic and Statistical Manual) in 1980.
The ICD-10, the International Classification of Diseases, published by the World Health Organisation in Geneva  regards the Narcissistic Personality Disorder (NPD) as “a personality disorder that fits none of the specific rubrics”. It relegates it to the category “Other Specific Personality Disorders” together with the eccentric, “haltlose”, immature, passive-aggressive, and psychoneurotic personality disorders and types.
The American Psychiatric Association, based in Washington D.C., USA, publishes the Diagnostic and Statistical Manual of Mental Disorders, fourth edition, Text Revision (DSM-IV-TR)  where it provides the diagnostic criteria for the Narcissistic Personality Disorder (301.81, p. 717).
The DSM-IV-TR defines Narcissistic Personality Disorder (NPD) as “an all-pervasive pattern of grandiosity (in fantasy or behaviour), need for admiration or adulation and lack of empathy, usually beginning by early adulthood and present in various contexts”, such as family life and work.
The DSM specifies nine diagnostic criteria. Five (or more) of these criteria must be met for a diagnosis of Narcissistic Personality Disorder (NPD) to be rendered.