Paroxysmal pruritus. Its clinical characterization and a hypothesis of its pathogenesis

In dermatologic literature generally, itching, that familiar sensation that evokes a desire to rub or scratch, has been attributed almost without exception to something occurring in the skin: e.g., an insect bite, ringworm, contact dermatitis, urticaria, lymphoma, provocation by bile salts in jaundice. Itching in such instances is almost invariably relieved quite promptly, even if only temporarily, by rubbing or scratching with only moderate vigor, not enough to damage the skin, or at most to damage it only superficially. No one scratches a mosquito bite, hives, ringworm, or even lichen planus to the point of bleeding and scarring. Winkelmann and Muller suggested in 1964, "In rare instances, the itching response does not reside in the skin...but may be analogous to phantom limb sensations." I believe that this is a common phenomenon that is characteristic of several familiar, common skin disorders, that can be readily identified from the patient's history, and that serves to explain some otherwise mysterious clinical features of those disorders; in particular, why they are regularly scratched to the point of oozing, bleeding, scarring, or lichenification.