Which psychiatric disorder often presents with intractable pruritus?

Delusions of parasitosis is the fixed belief that a patient is infested with living organisms in the absence of evidence of such infestation. Delusions of parasitosis often occurs as a sole psychological disturbance, but it may be associated with an underlying personality disorder, such as the obsessive-compulsive type. A physician must take care not to miss a true infestation. A careful history, thorough examination of the skin, microscopic review of “bugs” brought in by the patient, and, occasionally, a biopsy of the “bite” sites is needed. Establishing a dermatology-psychiatry liaison is helpful in establishing a diagnosis and selecting therapy. The neuroleptic pimozide, a blocker of dopamine receptors, is considered an effective treatment but requires careful monitoring because of several potentially serious side effects.

Driscoll MS, Rothe MJ, Grant-Kels JM, Hale MS: Delusional parasitosis: a dermatologic, psychiatric, and pharmacologic approach, J Am Acad Dermatol 29:1023–1033, 1993.