Many parallels between itch and pain research.

Acute itch is a commonplace sensation elicited by insect bites and certain plants, and normally serves as a protective warning signal. However, chronic itch is a frequent symptom of dermatologic conditions and a variety of systemic diseases (for recent review, see LaMotte et al., 2014). Current treatments for chronic itch are poor, leading to suffering and diminished quality of life. The situation is not so different from that of chronic pain, although much less attention has been devoted to chronic itch which is all too often regarded as a purely dermatological problem that can be treated adequately by application of external remedies. This series of mini-reviews on different aspects of this topic in a journal devoted to pain research shall also foster a better understanding of chronic itch problems within the community of pain researchers and therapists. The incidence of chronic itch and its socioeconomic costs have been the focus of recent epidemiological studies. In the United States, skin disease was estimated to affect upwards of one-third of the US population at any given time, imposing an economic burden of $96 Billion in 2004. A 2009 report from the US National Institutes of Health estimated chronic itch from atopic dermatitis alone to exact costs of approximately $3 Billion annually. A recent study reported a 22% lifetime prevalence of chronic itch among German citizens (Matterne et al., 2011). The negative impact of chronic itch is highlighted by Norwegian studies reporting an 8.8% incidence of chronic itch in adolescents, of whom 21.1% reported suicidal ideation (Halvorsen et al., 2012). This incidence of suicidal ideation is very similar to that of patients suffering from chronic pain, and markedly greater than that of subjects not suffering from chronic itch or pain (8.4%). Clearly, chronic itch is a major social and economic burden that demands research to establish more effective treatment strategies. In 2005, the International Forum for the Study of Itch (IFSI) was established as an organization bringing together clinicians and researchers with interest in all aspects of itch, and a common goal to better understand the basic mechanisms of itch for the development of improved, evidence-based treatments. IFSI has grown to a current membership of over 150 individuals, and has biennial meetings as well as a growing presence at many dermatology and other scientific meetings worldwide. IFSI sponsored a symposium at the 23rd World Congress of Dermatology held in Vancouver in June 2015. This issue of the European Journal of Pain presents a series of mini-reviews submitted by world leaders in clinical and basic science who gave presentations at the IFSI symposium. This series of mini-reviews is an excellent representation of the broad spectrum of current issues related to understanding the epidemiology, psychology, pathophysiology and clinical treatment of itch. There is a high prevalence of chronic itch associated with a variety of systemic diseases, including end-stage renal disease (ESRD) in patients undergoing kidney dialysis. Weisshaar reviewed recent studies that provide accurate estimates of the prevalence of chronic itch in ESRD (also known as uraemic itch). A recent cross-sectional study of over 800 ESRD patients reported a point prevalence of 25.2%, 12-month prevalence of 27.2% and lifetime prevalence of 35.2% of chronic itch in ESRD patients. This review provides valuable new information demonstrating the magnitude of debilitating chronic itch in ESRD that can be expected to only increase as the population ages. Chronic itch of ESRD and other causes are notoriously difficult to treat. Pongchareon and Fleischer provided an evidence-based analysis of efficacy of treatments for chronic itch of various aetiologies including uraemic itch. Using meta-analyses of randomized doubleblind placebo-controlled studies in which itch intensity was measured and longitudinally tracked, they reported that nalfurafine and gabapentin were effective for reducing uraemic itch, naltrexone reduced chronic itch from cholestasis and atopic dermatitis, and ursodeoxycholic acid reduced itch from intrahepatic cholestasis of pregnancy. Other potentially useful drugs require larger or better