Excerpt: "The core feature of a paranoid personality disorder (PPD) is a longstanding, pervasive pattern of mistrust in the motives of others. Persons with this disorder assume that others have malevolent intentions to harm, exploit, or deceive them, even when no objective evidence exists. They ruminate over unfounded suspicions that their family and friends are disloyal and will scrutinize these relationships for evidence of untrustworthiness. In particular they are prone to pathological jealousy of their spouse or lover. They are often reluctant to confide in others out of fear that anything they say will be used against them. This makes them appear interpersonally cold and aloof. They also tend to distort benign remarks into hidden meanings that are threatening and insulting. For example, they might respond to an offer for help with, "So you think I'm incapable of doing it myself!" People with this disorder often stubbornly refuse to forgive others for insults or injuries that they think they have received. They are swift to counterattack with hostility for such imagined offenses. In order to meet the criteria for a diagnosis of PPD, these symptoms must not occur as part of a psychotic disorder and must not be directly caused by a medical illness. PPD begins by early adulthood and typically endures for life."
Thurston, Nancy S., "Paranoid Personality Disorder." (1999). Faculty Publications - Grad School of Clinical Psychology. 286.