Delusions of parasitosis.

The fixed belief that one is infested with living organisms, in the absence of any objective evidence that such infestation exists, is termed "delusions of parasitosis." For most patients, this is a "monosymptomatic" disorder because there is no evidence of psychotic ideation in other areas of their lives. This overall normality of thought processes, together with exceptional strength of conviction regarding infestation, makes confirmation of a suspected diagnosis difficult. We want, and need, to be certain that a true infestation is not missed. This requires careful history taking, thorough examination of the skin, microscopic review of the material brought in by the patient and, occasionally, biopsy of lesions identified by the patient as "bite" sites. Establishment of a diagnosis is difficult enough, but it is even more difficult (usually impossible) to convince the patient that there are no "bugs" present. Attempts to have the patient visit a psychiatrist are virtually always rebuffed, leaving the clinician no choice but to begin therapy. Pimozide, a blocker of dopamine receptors, represents the pharmacological treatment of choice. The use of this drug is usually quite helpful, but relapse frequently occurs when treatment is stopped. For patients who will not take the drug, and for those who fail treatment, the best that can generally be achieved is the provision of a supportive environment. In such a setting, many of these patients eventually shift to a less troublesome chronic phase of their disease during which the delusion partially or even completely slips into the subconsciousness thus allowing for more normal daily functioning.