Aripiprazole in the treatment of primary delusional parasitosis

The review by Lepping et al ¹ points out the difficulty of engaging patients with primary delusional parasitosis in psychiatric treatment owing to their poor insight. Our clinical experience fully supports this. The authors emphasise the lack of randomised controlled studies in this field and the limited, but promising, anecdotal literature on the use of atypical antipsychotics. Their systematic review did not identify any reports of aripiprazole in the treatment of primary delusional parasitosis. However, since this review was accepted for publication, a case report has appeared reporting the successful use of aripiprazole in an 85-year-old woman with primary delusional parasitosis. ²

Aripiprazole has a unique pharmacological profile that includes partial agonist activity at dopamine D₂ and serotonin 5-HT_1A receptors. It has a favourable side-effect profile relative to other antipsychotics. ³ It is non-sedating and has little propensity to cause weight gain, extrapyramidal symptoms, prolactin elevation and metabolic disturbance. However, it can cause nausea and akathisia in some patients. The favourable tolerability profile may be a particular benefit in primary delusional parasitosis as these patients are often reluctant to consider antipsychotic treatment and tolerate medication poorly.

Aripiprazole has a long half-life (about 60 h) compared with other oral antipsychotics, ⁴ which means that occasional missed doses are less likely to affect clinical outcome. Consequently, aripiprazole may be particularly useful when intermitted adherence with medication is a problem, a situation often encountered in primary delusional parasitosis. Interestingly, in the five main studies of antipsychotic treatment of primary delusional parasitosis identified by Lepping et al, ¹ the highest remission rate (73%) was in the only study that assessed antipsychotic depots. ⁵ Although the small sample sizes limit the value of cross-study comparisons, this result is consistent with the view that medication adherence is poor in primary delusional parasitosis and that treatments that can overcome this, in this case a depot antipsychotic, can lead to better outcomes.

In summary, although further evidence is needed to establish the efficacy of aripiprazole in primary delusional parasitosis, it seems reasonable to consider this drug when discussing treatment choices with patients.