Pruritus in certain internal diseases.

In the past it was widely believed that pain and itching are transmitted by the same nerve pathway with the low intensity stimulation of unmyelinated polymodal C fibers resulting in sensation of pruritus whereas high intensity stimulation causing pain. In recent experiments however, stimulation of single unmyelinated C fibers led to the identification of two kinds of fibers. Stimulation of most of these fibers induces pain, whereas a small number of fibers provoke the sensation of itching. Pruritus is an unpleasant sensation, often accompanied by scratching. It may present due to a number of cutaneous diseases or internal disorders. Pruritus may be caused by some chemical substances as histamine, prostaglandins, proteases and substance P. This review describes the existence of pruritus in different internal disorders. It is quite important the reason of pruritus to be discovered, for the application of an adequate therapy.