Integration: Unifying Concept
Atopic dermatitis is factitious dermatitis that occurs in persons who are atopic, to wit, those with a personal or family history of allergic rhinitis, allergic conjunctivitis, or allergic asthma. Such people also have a predilection for allergic urticaria. The state of atopy is determined genetically, and one of the cardinal symptoms of it is pruritus.
Persons who are atopic itch easily and in response to many causes. For example, a person who is not atopic has no difficulty wearing mohair, but on an atopic person a mohair sweater causes extraordinary pruritus, which is greeted by bouts of intense scratching. When an atopic person, whether child or adult, becomes unhinged emotionally at a particular moment, frenzied scratching of wildly pruritic skin may ensue, and, in minutes the entire integument may be transformed by the effects of fingernails. Those effects may range everywhere and into an erythroderma. If, however, the hands of an atopic could be shackled, the skin would be free of signs of rubbing and scratching that have come to be known, erroneously, as atopic dermatitis. This fact was demonstrated experimentally more than 100 years ago.
Lichen simplex chronicus appears in the skin of people who may or may not be atopic, and always as a consequence of mechanical trauma, such as in a variety of circumstances where trauma occurs expectedly. It might, for example, appear beneath the chin where a violin “rests” and on the elbows of a microscopist who “reads” sections of tissue for many hours daily. Lichen simplex chronicus, therefore, is not at all contingent on whether or not a person is atopic; vigorous rubbing of skin over the course of months or years is the common denominator.
The same principle applies to prurigo nodularis. When that condition occurs on the knees of surfers, it is called “surfers nodules,” on the nose or behind the ear as a consequence of the pressure applied to the skin by parts of eyeglasses “granuloma fissuratum,” and as a consequence of a prosthesis utilized because of amputation of a leg, “pressure papule.” When pressure is applied to the helix or the antehelix of an ear damaged by the effects of ultraviolet light, the analogue of prurigo nodularis that develops is called “chondrodermatitis nodularis helicis,” a misnomer. It is not truly a chondrodermatitis, but rather a papule that results from pressure against the cartilage, even pressure as light as is caused by sleeping on an ear.