Psychologist Theodore Millon has proposed five subtypes of paranoid personality:

Differential diagnosis
Paranoid personality disorder can involve, in response to stress, very brief psychotic episodes (lasting minutes to hours). The paranoid may also be at greater than average risk of experiencing major depressive disorder, agoraphobia, social anxiety disorder, obsessive-compulsive disorder and substance-related disorders. Criteria for other personality disorder diagnoses are commonly also met, such as: schizoid, schizotypal, narcissistic, avoidant, borderline and negativistic personality disorder. Treatment
Because of reduced levels of trust, there can be challenges in treating PPD. However, psychotherapy, antidepressants, antipsychotics and anti-anxiety medications can play a role when a person is receptive to intervention. Epidemiology
PPD occurs in about 0.5–4.4% of the general population. It is seen in 2–10% of psychiatric outpatients. In clinical samples men have higher rates, whereas epidemiologically there is a reported higher rate of women. History
Paranoid personality disorder is listed in DSM-V and was included in all previous versions of the DSM. One of the earliest descriptions of the paranoid personality comes from the French psychiatrist Valentin Magnan who described a "fragile personality" that showed idiosyncratic thinking, hypochondriasis, undue sensitivity, referential thinking and suspiciousness.Closely related to this description is Emil Kraepelins description from 1905 of a pseudo-querulous personality who is "always on the alert to find grievance, but without delusions", vain, self-absorbed, sensitive, irritable, litigious, obstinate, and living at strife with the world. In 1921, he renamed the condition paranoid personality and described these people as distrustful, feeling unjustly treated and feeling subjected to hostility, interference and oppression.
Paranoid personality disorder (PPD) is a mental illness characterized by paranoid delusions, and a pervasive, long-standing suspiciousness and generalized mistrust of others. People with this personality disorder may be hypersensitive, easily insulted, and habitually relate to the world by vigilant scanning of the environment for clues or suggestions that may validate their fears or biases. They are eager observers. They think they are in danger and look for signs and threats of that danger, potentially not appreciating other interpretations or evidence.They tend to be guarded and suspicious and have quite constricted emotional lives. Their reduced capacity for meaningful emotional involvement and the general pattern of isolated withdrawal often lend a quality of schizoid isolation to their life experience. People with PPD may have a tendency to bear grudges, suspiciousness, tendency to interpret others actions as hostile, persistent tendency to self-reference, or a tenacious sense of personal right. Patients with this disorder can also have significant comorbidity with other personality disorders, such as schizotypal, schizoid, narcissistic, avoidant and borderline. Causes
A genetic contribution to paranoid traits and a possible genetic link between this personality disorder and schizophrenia exist. A large long-term Norwegian twin study found paranoid personality disorder to be modestly heritable and to share a portion of its genetic and environmental risk factors with the other cluster A personality disorders, schizoid and schizotypal.Psychosocial theories implicate projection of negative internal feelings and parental modeling.