100 years of delusional parasitosis. Meta-analysis of 1,223 case reports.

Delusional parasitosis (DP) is mostly described in single cases or small samples. Data on epidemiology, nosological classification, therapy and course are therefore difficult to interpret. A thorough literature review is recommended to delineate common features of the syndrome. All case reports concerning DP (except toxic forms) were collected and analyzed according to a standardized protocol. DP is a disorder which may occur in every period of life but is much more frequent in older subjects. Sex differences with a predominance of females increase with age. Mean duration of delusion was 3.0 +/- 4.6 years (median: 1 year). Social isolation seems to be more a premorbid feature than a secondary phenomenon related to the delusion. Diagnostic classification revealed a high proportion of so-called 'pure' forms ('delusional disorders' in DSM-III-R or ICD-10) but the syndrome was also reported in schizophrenia, affective or organic psychosis or even as a neurotic symptom. Frequency of induced DP can be estimated between 5 and 15%. Course of DP is not so unfavorable as commonly thought; in about half the patients a full remission was described during the observation period or at catamnesis. Short preclinical courses may indicate better outcome. Comparing the patients of the prepsychopharmacological era (before 1960) with those after, the rate of full remissions increased from 33.9 to 51.9%.