![]() Pruritus is a frequent manifestation in patients with liver diseases and intra- or post- hepatic cholestasis 10. ![]() This same population is quite likely to be exposed to many of the other etiologic factors relating to pruritus ranging from nutritionally related xerosis (dry skin) to radiation desquamation, chemotherapy and biologic agent–induced side effects, antibiotic reactions, and other drug sensitivities. People receiving cytotoxic chemotherapy, irradiation, and/or biologic response modifiers for treatment of malignancy are likely to experience pruritus. Higher kininogen in Hodgkin’s lymphoma, release of histamine or bradykinin precursors from solid tumors, and serotonin in carcinoid may all be the agents, causing pruritus. Released from circulating basophils histamine and leukopeptidase - from white blood cells - may trigger pruritus associated with lymphomas and leukemias. Malignant, hepatic, and renal diseases, are thought to produce itching by circulating toxic substances. It is thought that spinal modulation of afferent stimuli and central mechanisms may play a role in the relief of itch 5, 6 Pathogenesis of pruritus associated with underlying disease states are varied. Other physical stimuli such as heat, cold, vibration, and ultraviolet radiation diminish itching and increase the release of proteolytic enzymes, blocking the itch-scratch-itch chain 6 – 8. Scratching may enhance the sensation of itching, creating a itching-scratching-itching cycle. Scratching probably generates sensory impulses that disrupt circuits in some areas of the spinal cord. The mechanism of this relieve by scratching is unknown. After scratching, pruritus may be relieved for 15 to 30 minutes. Scratching is modulated at the corticothalamic center as a spinal reflex. The motor response of scratching follows the itching. Factors that are believed to enhance the sensation of pruritus include dryness of the epidermis and dermis, anoxia of tissues, dilation of the capillaries, irritating stimuli, and psychological responses 5, 7. Thalamocortical tracts of tertiary neurons are believed to relay the impulse through the integrating reticular activating system of the thalamus to several areas of the cerebral cortex. The itch impulse is transmitted from peripheral nerves to the dorsal horn of the spinal cord, across the cord via the anterior commissure, and ascending along the spinothalamic tract to the laminar nuclei of the contralateral thalamus. Some of the substances act directly on the free nerve ending, while others act indirectly through mastocytes or other cells 7. Pruritus is provoked or enhanced by a number of chemical substances such as histamine, prostaglandins, proteases, cytokines, neuropeptides, including substance P, and bile salts. The following data are in favor of the concept that receptors for itching and pain are different: itching provokes scratching, while pain causes a withdrawal response morphine relieves pain, but can cause pruritus removal of the epidermis and upper dermis abolishes itching, but not pain heating of skin to 41° C relieves itching, but not pain 5, 6. Now two kinds of fibers have been identified: most of these fibers produce pain, whereas a small number of them produce the sensation of itching upon stimulation. It has been a long time since the general belief that itching and pain are transmitted by the same nerve pathway, with low intensity stimulation of unmyelinated polymodal C fiber resulting in sensation of pruritus whereas high intensity stimulation causing pain. Pruritus may be acute or chronic, localized or generalized 3, 4. The intensity can be mild, moderate or severe with sleep disorders, discomfort and increased irritability, disturbance of daily activity or general stress. It must be underlined that pruritus is only a symptom of a number of disease and is generally a subjective sensation, sometimes accompanied by crusts, excoriations, hyperpigmentations, lichenification with thickening, pyodermia, increased skin creasing and burnished nails 1, 2. Pruritus must be differentiated from tickling, burning, pain and touch. Pruritus can be a physiological event as well, if the provoked scratching removes a potentially dangerous agent, or if it is due to some drugs or psychic diseases 2. ![]() Of course the word "unpleasant" means different things to different people 1. ![]() A simple definition of pruritus or itching is "the unpleasant skin sensation that frequently provokes scratching". ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |