Shared psychotic disorder in delusional parasitosis.

Delusional parasitosis (DP) is associated in 5-15% with shared psychotic disorder (SPD). Little systematic information is available about this particular aspect of the syndrome. A thorough review of all published cases with DP was carried out. 68 case histories of SPD were identified (5.67%). The data of these patients were compared with those of their inducers (n = 44) and with the data of DP patients, who did not transfer their delusional beliefs to others (n = 1,155). Approximately 30% of the psychotic dyads were reported from public health departments. The sex ratio was balanced in the SPD group, but showed a clear preponderance of females in the other two groups. SPD patients and their inducers reported more frequently visual illusions or hallucinations and located the animals correspondingly upon the surface of the skin. No diagnostic differences were found between the inducers and those who had DP but did not induce SPD in others. Albeit 50% of the SPD patients did not receive any treatment except separation from the inducer, the remission rate in this group was 93%.