Delusional parasitosis (DP) is a rare but debilitating condition characterized by the false belief that one is infested by parasites, mice and vermin. It occurs particularly in middle-aged or elderly men who live alone. Primary DP occurs on its own, whereas secondary DP occurs in conjunction with another mental or physical health problem. A review of 63 case studies looked into the effectiveness of second-generation antipsychotics (SGAs) in treating DP. It found that the drugs were effective after about 10 days with the maximum effect occuring after 6 weeks. For those people who stuck with treatment for 8 weeks all cases responded at least partially. Partial or full remission was reached in 69% of the situations where an SGA was introduced. Secondary DP was more likely to respond to SGAs than primary DP. Risperidone and olanzapine were most widely used and resulted in full or partial remission in 69 and 72% of cases respectively. More research is needed into this topic as such reviews of case studies are considered less reliable than other research.
Freudenmann, Roland W. and Lepping, Peter - Second-generation antipsychotics in primary and secondary delusional parasitosis: outcome and efficacy Journal of Clinical Psychopharmacology October 2008, 28(5), 500-508