Narcissistic personality disorder (NPD) is a personality disorder defined by the Diagnostic and Statistical Manual of Mental Disorders, the diagnostic classification system used in the United States, as "a pervasive pattern of grandiosity, need for admiration, and a lack of empathy." [ 1 ]
The narcissist is described as being excessively preoccupied with issues of personal adequacy, power, and prestige. [ 2 ] Narcissistic personality disorder is closely linked to self-centeredness.
Pathological narcissism occurs in a spectrum of severity. In its more extreme forms, it is narcissistic personality disorder (NPD). NPD is considered to result from a person's belief that they are flawed in a way that makes them fundamentally unacceptable to others. [ 9 ] This belief is held below the person's conscious awareness; such a person would typically deny thinking such a thing, if questioned. In order to protect themselves against the intolerably painful rejection and isolation that (they imagine) would follow if others recognized their supposedly defective nature, such people make strong attempts to control others’ view of them and behavior towards them.
Pathological narcissism can develop from an impairment in the quality of the person's relationship with their primary caregivers, usually their parents, in that the parents were unable to form a healthy, empathic attachment to them.  This results in the child conceiving of themselves as unimportant and unconnected to others. The child typically comes to believe they have some personality defect that makes them unvalued and unwanted. [ 10 ]
To the extent that people are pathologically narcissistic, they can be controlling, blaming, self-absorbed, intolerant of others’ views, unaware of others' needs and of the effects of their behavior on others, and insistent that others see them as they wish to be seen. [ 7 ]
People who are overly narcissistic commonly feel rejected, humiliated and threatened when criticised. To protect themselves from these dangers, they often react with disdain, rage, and/or defiance to any slight criticism, real or imagined. [ 11 ] To avoid such situations, some narcissistic people withdraw socially and may feign modesty or humility. In the case of feeling the lack of admiration, adulation, attention and affirmation the person can also manifest wishes to be feared and to be notorious (narcissistic supply).
Though individuals with NPD are often ambitious and capable, the inability to tolerate setbacks, disagreements or criticism, along with lack of empathy, make it difficult for such individuals to work cooperatively with others or to maintain long-term professional achievements. [ 12 ] With narcissistic personality disorder, the person's perceived fantastic grandiosity, often coupled with a hypomanic mood, is typically not commensurate with his or her real accomplishments.
The exploitative, sense of entitlement, lack of empathy, disregard for others, and constant need for attention inherent in NPD adversely affect interpersonal relationships.