Delusional parasitosis, or delusions of parasitosis, is a form of psychosis in which the patient believes that he or she is suffering from parasitic infestation, when in reality there is no such infestation. Often, the patient describes the imagined parasites as bugs crawling over or under the skin. Formication, the medical term for a crawling sensation on the skin, such as the "pins and needles" that can arise when circulation to an extremity is temporarily cut off, may be the basis for some cases of delusions of parasitosis.
Delusional parasitosis is sometimes referred to as Ekbom's syndrome, after 20th century Swedish neurologist Karl Axel Ekbom. However, Ekbom worked on both delusions of parasitosis and restless leg syndrome, and either condition may be referred to as Ekbom's syndrome. The two disorders are very different, however, as restless leg syndrome has physical causes and delusional parasitosis is a psychological condition.
Patients with delusional parasitosis often collect what they believe to be evidence of their infestation, such as small marks on the body or clothing. They are capable of injuring themselves, for example through excessive scratching, and sometimes convince others, such as those they live with, that they are also infested. A variety of the delusion, delusory cleptoparasitosis, is characterized by a belief that one's dwelling is infested with parasites, rather than one's person.
Delusional parasitosis may be divided into three categories. These are primary, secondary functional, or secondary organic. In primary delusional parasitosis, the psychosis presents on its own, without any accompanying disorders or causes. In the secondary functional variety, another psychiatric condition is present, such as schizophrenia or depression.
In secondary organic delusions of parasitosis, the psychosis is caused by a medical illness, medication, or recreational drug use. Some medical conditions that can cause delusional parasitosis include diabetes mellitus, tuberculosis, cancer, and neurological disorders. Menopause, allergies, poor nutrition, and drug abuse can also be underlying causes of delusions of parasitosis.
Patients with delusions of parasitosis are often misdiagnosed or misunderstood, as they typically do not realize that their condition is psychological. They are more likely to seek help from a dermatologist than a psychiatrist and may refuse psychiatric treatment. If delusional parasitosis is a secondary condition, it is treated by treating the primary condition, or cause. Whether primary or secondary, delusions of parasitosis are often very difficult to treat because the patient rejects a psychological explanation of his or her symptoms.