Delusional parasitosis is a mistaken belief that parasites have infested the body.
People with delusional parasitosis have an unshakable, false belief that they are infested with insects, worms, mites, lice, fleas, or other organisms. Some people also believe the parasites have infested their home, surroundings, and clothing. They often provide vivid descriptions of how the organisms enter their bodies via their skin and other body openings and move around. The sensations of itching, crawling, and irritation are very real to them. In an effort to rid themselves of these sensations, people may scratch, pick at, or mutilate their skin enough to cause sores or ulcers. Such sores then sometimes become infected. Other people apply various chemicals and/or disinfectants to their skin. Such chemicals may cause skin irritation or allergic reaction.
People bring samples of hair, skin, and debris, such as dried scabs, dust, and lint, to their doctor to inspect and to prove the infestation is real. People may put the samples on a microscope slide or carry them in a container or matchbox. Delusional parasitosis most often affects people over 50 and women but is very rare.
Some people with delusional parasitosis may have a disorder that causes them to excessively worry about their health (hypochondriasis—see Hypochondriasis) or may have become aware of some parasitic disorder (for example, scabies) from the media or may have been in contact with a person infected by it. Some people with delusional parasitosis also have a mental disorder, such as schizophrenia, depression, anxiety, or obsessive-compulsive disorder, but most do not. Abuse of certain drugs (such as cocaine or methamphetamine) or withdrawal after prolonged use of alcohol can also lead to delusional parasitosis.
Diagnosis is sometimes difficult because many actual skin disorders, such as allergies, dermatitis, or real parasites, also cause the itching sensations. Also, skin sores or irritation caused by the person's scratching and use of chemicals may look like other skin disorders.
Doctors base the diagnosis on a physical examination and the person's history, including any history of drug use or mental disorders. Doctors may do skin scrapings and sometimes blood tests to rule out real infestations and other diseases. If a real infestation has been ruled out, examination by a psychiatrist may be helpful to determine whether delusional parasitosis is part of a mental disorder.
Treatment is best coordinated between a doctor who specializes in skin disorders (called a dermatologist) and a psychiatrist. The dermatologist does a thorough evaluation to make sure that there are no actual parasites. The person is then referred to a psychiatrist so that their delusion can be treated. Antipsychotic drugs such as risperidone and haloperidol can be very effective. However, people often refuse to accept psychiatric help and instead visit many different doctors in a futile search for a treatment that will eradicate the parasites they imagine.
Last full review/revision June 2013 by James G. H. Dinulos, MD