In delusional parasitosis, patients mistakenly believe that they are infested with parasites.

Patients have an unshakable belief that they are infested with insects, worms, mites, lice, or other organisms. They often provide vivid descriptions of how the organisms enter their skin and move around their bodies, and bring samples of hair, skin, and debris such as dried scabs, dust, and lint on slides or in containers (the matchbox sign) to prove that the infestation is real. The condition is considered a somatoform type of delusional disorder. Patients may have other psychiatric or physical disorders (eg, structural brain disorders, toxic psychosis).

Diagnosis is suspected by history and clinical examination. Evaluation requires ruling out true infestations and other physiologic disease by physical examination and judicious testing, such as skin scrapings and other tests as clinically indicated.

It is important to establish an empathetic and supportive relationship with the patient. Although often rejected, the most effective treatment is with antipsychotic drugs (see Schizophrenia and Related Disorders: Conventional Antipsychotics). Typically, the patient seeks confirmation that the drug treats the infestation itself, and any suggestion that the treatment is for something else is met with resistance, rejection, or both. Thus, effective treatment often requires diplomacy and a delicate balance between offering proper treatment and respecting the patient's right to know.

Last full review/revision March 2013 by James G. H. Dinulos, MD