Delusional Disorder

Delusional disorders (according to the Diagnostic and Statistical Manual of Mental Disorders [DSM]) or persistent delusional disorders (according to the International Classification of Diseases [ICD]) have succeeded the old concept of paranoia,^1,2 which was the most central concept in psychiatry in the 19th century. The paranoia concept was very broad and unspecific, and hence, according to Emil Kraepelin,³ 70–80 % of all mentally ill patients were diagnosed with paranoia. After Kraepelin’s reform of the concept at the end of the 19th and the beginning of the 20th century, it became much narrower and more specific, so that its frequency went down to approximately 1 %, which is compatible with the frequency estimated according to modern criteria. Because of the confusion regarding the term and the concept of paranoia, George Winokur⁴ suggested the term ‘delusional disorder’, meaning exactly the same as ‘paranoia’ after Kraepelin’s reform. In 1987, the DSM, third edition revised (DSM-III-R) and, a few years later, the ICD-10,⁵ adopted the term ‘delusional disorder’.

Although, as Berrios¹ pointed out, the new term is not unproblematic, the linguistic adaptation was necessary because the term paranoia was used very unspecifically and unprofessionally. The term ‘paranoid’ was used, especially in English-speaking countries, instead of the term ‘paranoic’. But paranoid is not the same as paranoic: paranoic always refers to paranoia, but paranoid means ‘something similar to paranoia, which is not exactly paranoia’. Paranoid schizophrenia, for example, means a schizophrenia-type-like paranoia, but not exactly the same, because additional symptoms (schizophrenic symptoms) can be detected. Another example is ‘paranoid personality’, a term used to describe a personality exhibiting symptomatology like paranoia, but which is not exactly paranoia, due to the criteria of a personality disorder. The same applies to ‘paranoid organic psychosis’. So it can be said that a paranoid individual may be a patient, but is not necessarily one, whereas a paranoic person is always a patient – a patient with a mental disorder, namely paranoia or delusional disorder.²

Definition and Diagnosis
Delusional disorder (as well as paranoia) can be defined as a mental disorder characterised by wrong, unfounded or uncorrectable convictions having a priori evidence, whereas other mental and personality domains usually remain intact. Delusional disorders are usually monosymptomatic and monothematic. That means that the exhibited delusion is the only relevant psychopathological symptom and the topic of the delusion refers to only one aspect, for instance jealousy, love or persecution. The ICD-10⁵ uses the term ‘persistent delusional disorder’ and the DSM, fourth edition (DSM-IV)⁶ the term ‘delusional disorder’. Both definitions are practically identical. The only relevant difference is the duration: the ICD-10 demands a duration of at least three months (see Table 1), whereas the DSM-IV demands a duration of only one month (see Table 2). However, this difference is only theoretical, as delusional disorder is usually persistent. The definition of delusional disorder proposed for the DSM, fifth edition (DSM-5)⁷ will most probably be the same as in the DSM-IV.

Apart from the above-mentioned specific delusional disorders, a plethora of phenomenological types, such as misidentification syndromes or culture-related syndromes, have been described. Many of these, however, are not autonomous and autochthonous delusional disorders, but a symptom of other major mental disorders such as schizophrenia, mood disorder or organic psychotic disorder.