Pruritus of Psychologic Origin

Pruritus occurring in the absence of visible skin disease is termed "essential" (or idiopathic) pruritus. Excoriations may or may not be present but, if present, will always occur without associated primary lesions. Thus, patients will indicate that at the time they began scratching, there was no visible skin disease. Essential pruritus can be divided into three subgroups: pruritus occurring as a result of underlying systemic disease, pruritus associated with "nondetectable" skin disease, and pruritus of purely psychologic origin.

Pruritus Associated with Systemic Disease

Generalized itching may be an early presenting sign (and thus a diagnostic clue) for polycythemia vera, Hodgkin's disease, and some types of hepatic disease. Pruritus in polycythemia vera is said to be particularly prominent following the ingestion of alcohol or the use of hot water for bathing. The pruritus of Hodgkin's disease may be related to the presence of xerosis since acquired ichthyosis is sometimes concomitantly present. Pruritus is often a prominent, early indicator of biliary cirrhosis, but in most other forms of hepatic dysfunction, itching occurs late in the course of the disease. The itching in hepatic disease was originally believed to be related to increased tissue levels of bile salts, but this explanation now seems unlikely.

Generalized pruritus occurs late in the course of pregnancy and in end-stage chronic renal disease. The itching in pregnancy is probably related to the mild cholestatic hepatic changes that are normally present in pregnancy. Hormonal factors and simple stretching of the skin may also playa role. The pruritus associated with chronic renal failure is often extremely severe. The cause of this pruritus is unknown, but reported improvement following parathyroidectomy suggests that imbalances in calcium and phosphorus metabolism may play a role. Dialysis alone does not usually lead to much decrease in the severity of the itching. Itching also occurs with diabetes mellitus, iron deficiency, and both hyperthyroidism and hypothyroidism.

Pruritus Associated with Nondetectable Skin Disease.

Excess dryness (xerosis) of the skin is an extraordinarily common cause of generalized pruritus. Xerosis sufficient to cause itching is seen in a variety of circumstances. People who bathe or shower more than once a day often complain of itching. This is particularly likely to occur when hot water and soap are liberally used. Xerosis also occurs in very dry environments even without excess bathing. Thus it can be a problem in the low humidity of desert climates and in winter climates where dry, forced air heating is used. Xerosis also is a component of atopy and aging. In both situations, inadequate cutaneous lipid production enhances moisture evaporation and leads to a drier than normal stratum corneum.

Sweat retention and other forms of mechanical irritation such as occur during contact with wool clothing, fiberglass spicules, and some plants may also be followed by itching. These mechanical factors seem to cause more problems for atopics than for people with "normal" skin.

Patients with pediculosis pubis (pubic lice) frequently report itching in the absence of visible skin lesions. Close observation reveals the presence of lice and adherent small white larvae (nits) on the hair shafts. Treatment is easily accomplished through use of lindane (Kwell) or synergized pyrethrins such as R.I.D. The latter has the advantage of being a nonprescription product.

Patients with mastocytosis may have episodes of generalized itching. This itching is usually accompanied by the presence of flushing or urticaria. Careful examination of the skin often reveals minute, brown, easily overlooked papules that are barely elevated above the surface of the surrounding skin. The use of standard HI blocking antihistamines, cimetidine, disodium cromoglycate, or psoralen-ultraviolet light (PUVA) therapy may be of help in the symptomatic treatment of this disease.

Pruritus of Psychologic Origin

A considerable portion of patients with essential pruritus have pruritus of psychologic origin. Some of these patients have easily detectable and rather severe psychiatric disorders. For instance, some patients insist that their itching is due to the presence of "bugs" or "worms" that are crawling about in the skin (delusions of parasitosis). Careful examination of their skin and of the material they have removed from their skin invariably fails to reveal any such organisms. These patients resist rational explanation and also refuse to accept psychiatric consultation. Instead, they seek out yet one more physician in an attempt to get someone to support their belief. It is appropriate to treat the pruritus symptomatically and to offer psychotropic medication, but I believe it is inadvisable to offer medications designed to kill the bugs, since, after a brief period of placebo effect, the problem will return, now reinforced by the belief that the physician had indeed found something worth treating.

Most other patients with psychogenic pruritus have considerably less psychic disability. A rough estimate of the severity of psychic dysfunction can be made on the basis of how severely the skin is damaged by scratching. Thus those with many "neurotic" excoriations and those with multiple scratch papules (prurigo nodularis) seem more troubled than those with no visible sign of scratching. Anxiety, depression, or both may be present. A program of counseling or behavior modification, together with appropriate psychotropic medications will often be of help.

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Pruritus of Psychologic Origin
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