Delusional parasitosis: 102 case studies in Japan

In order to examine the clinical characteristics of delusional parasitosis in a large sample, 102 cases were collected from the Japanese literature reported so far. There were 30 patients with somatically-based psychosis, 12 with endogenous psychosis, 7 with induced psychosis, and 53 with pure delusional parasitosis. Age at onset, clinical features, CT and EEG findings, therapy, course, and prognosis were compared between the pure type and the other groups. The majority of patients fell ill after the age of 50. A sex difference (with a predominance of females) was found only in pure delusional parasitosis. The pure type patients often insisted that they actually saw the parasites (43%), regarded skin particles or the like as parasites (42%), and the parasites had personalities (23%). Half of the pure type patients had some CT and EEG findings, and 82% of those with some CT findings and 78% of those with some EEG findings claim to have seen parasites. As for the course, they were mainly phasic, not always chronic and progressive. These pure-type patients sometimes had delusions of persecution and self-reference experiences, and considered infestation by parasites to be part of a conspiracy against them. They often had symptoms thought to be schizophrenic, and also often yielded some biological findings. Therefore, a nosological classification of these patients should be postponed, and both psychopathological and biological studies should be carried out continuously from now on.