Delusional parasitosis (DP) is a rare psychiatric disorder, predominantly observed in middle aged and elderly patients. It can manifest itself as an isolated delusional disorder (primary DP), as a symptom of another psychiatric disorder or as an organic or toxic psychosis. The typical antipsychotic pimozide was traditionally considered to be the gold standard for treating DP. Compared with pimozide, atypical antipsychotics have many advantages in terms of tolerability, but their effectiveness has only been shown in a few case reports, which do not differentiate between primary and other forms of DP.
We present the case of a 77-year-old woman with primary DP who responded markedly to the atypical antipsychotic olanzapine (2.5 mg daily). She was treated in a psychiatric outpatient department with a follow-up period of 3.5 years. This is the first report of a successful olanzapine mono-therapy in primary DP in such a setting and the longest follow-up period ever reported. The need for maintenance treatment was demonstrated. Olanzapine in age-adapted doses should be considered as an alternative treatment. This paper also provides a review of all published cases in which primary DP was treated with atypical antipsychotics.