Pruritus: from Pathophysiology to Therapeutics.

Pruritus (itch) is defined as an unpleasant sensation leading to the need to scratch. It is therefore a sensation that is distinct from pain but whose repercussions are quite equivalent. Pruritus and pain are differentiated not only by the induction of different reactions (scratching, withdrawal) but also by rather opposite effects of heat and cold or completely opposite effects of opiates. The treatments are very different. In the skin and some mucosa, there are specific pruritus receptors (pruriceptors) and then there are specific pathways leading the "pruritus" signal to different areas of the brain. These pathways are shared with the pain pathways or not. The mechanisms of peripheral and central sensitization to pruritus are increasingly well understood, with the clinical consequences of chronic pruritus, alloknesia and hyperknesia. Pain can inhibit pruritus by activating interneurons. It can sometimes coexist with pruritus, particularly in the case of neuropathic pruritus. The causes of pruritus are most often dermatological but other causes are also possible: renal, hepatic, endocrine, metabolic, hematological, paraneoplastic, neurological, psychic, iatrogenic or mixed. Until now, the management of pruritus has been disappointing. Antihistamines are rarely effective. Gabapentinoids may be used. Recent progress in research is opening up new avenues: κ-agonists, µ-antagonists, anti-IL31, anti-IL4/13, NK1 inhibitors, anti-Jak, etc. A network of antipruritus centers inspired by the organization of pain management centers would probably be very useful. [ABSTRACT FROM AUTHOR]