JMIR Publications

ABSTRACT

Delusional parasitosis (DP) is a rare psychotic disorder where individuals firmly believe they are infested with parasites despite no medical evidence. It may be shared among close contacts, termed folie à deux when two individuals are affected or folie à trois when three individuals share the delusion. DP’s somatic focus often leads patients to dermatologists, causing delayed diagnosis and unnecessary antiparasitic treatments. Herein, we present two familial cases of shared DP. In both cases, patients exhibited the matchbox sign, presenting non-parasitic materials as "evidence" of infestation. Dermatological and psychiatric evaluations excluded organic causes, diagnosing primary DP. Treatment with antipsychotic medications led to symptom remission. Psychoeducation was critical in preventing relapse in secondary cases. DP with shared delusions is often misdiagnosed, requiring dermatologists to recognize it early. A multidisciplinary approach, combining psychiatric care and psychoeducation, is essential for effective management and preventing reinforcement of delusional beliefs.