LAS VEGAS – Improved understanding of itching and best practices in management of the condition may lead to U.S. medical centers specializing in treating pruritus.
A recent gathering of experts convened by the National Institutes of Health (NIH) may be the first step in this direction, Dr. Timothy G. Berger said at the meeting.
The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) pulled together 50 physicians to discuss the topic of pruritus. One of a series of roundtable discussions held by NIAMS, this was the first to focus on itching. A summary of the meeting and a list of attendees has been posted on the NIAMS Web site, NIAMS media liaison Trish Reynolds said in an interview.
“These things are usually followed by calls for proposals,” said Dr. Berger of the University of California, San Francisco (UCSF), who did not attend the roundtable discussion. “The NIH is moving to a model of having major itch referral centers at several sites.”
Patients with itch would be referred to a center where their tissue samples and data could be stored and analyzed while they get expert treatment. “There will be direct translational benefits” from this approach, he predicted.
These centers would be patterned after two models – referral centers for pain, and European itch centers. The U.S. itch centers might first appear at UCSF; Washington University, St. Louis; and Harvard University, Boston, he said.
“In Europe, every patient with itch goes to a medical center for itch, is seen in a standard way, and has a defined database established about that patient. They now have tens of thousands of itch patients of various types logged into this database,” and data it provides are helping to build greater understanding of the problem of itching, Dr. Berger said.
One of the key insights into itching in recent years has been the understanding that chronic itch is like chronic pain. Chronic itch is thought to begin peripherally but then trigger anatomic changes in the CNS that make treatment much more difficult. “This suggests that we will have agents that will act both peripherally and centrally” to ease itching, he said. “We're now at the verge of being able to do something about itching.”
Chronic itching should be treated aggressively because once central sensitization occurs, it is very, very hard to manage, he advised. Chronic itching has a huge impact on quality of life, earning the same scores by patients as the reduced quality of life reported by patients with chronic renal failure on dialysis.
Once itch is chronic, the threshold for sensation of itch is reduced. “Even if you make their rash better, they still itch,” he said. Itch intensity increases with chronicity, producing more itch from the same rash. Even when the skin is clear, patients may have short bursts of spontaneous itch. In atopic dermatitis and perhaps some other forms of itchy lesions, patients may scratch themselves raw because inflammatory mediators of pain are perceived as itch.
“This whole system is miswired” in chronic itch, Dr. Berger said.
Perceived itch is a delicate interaction between the skin, nerves, and immune system, and treatments may target one or more of these pathways. The most common medication for chronic itch is second-generation antihistamines, in higher doses than used for the approved indication of allergic rhinitis. “These substances also block other inflammatory mediators that may be important for itch, so they may have benefit beyond what we know,” Dr. Berger said.
Neuroleptic medications for itch include amitriptyline or other tricyclic antidepressants, gabapentin, pregabalin, duloxetine, or thalidomide for prurigo nodularis. “These act primarily on the neural axis,” he said.
Central-acting agents include paroxetine, amitriptyline, doxepin, or mirtazapine. In a large European cohort, 6-9 months of treatment with paroxetine reduced chronic itch by 75% in 70% of patients. “It's now become one of our drugs to treat itch, and is the treatment of choice for itch in polycythemia vera,” he said.
Research has shown that patients who have liver disease can develop itch caused by abnormalities in opiate metabolism, leading some clinicians to treat chronic itch with naltrexone, butorphanol, or other agents that act on the opiate pathway.
Phototherapy also has been used to treat chronic itch, including narrow-band UVB, psoralen plus UVA, or broadband UVB for itch associated with renal disease. “Phototherapy probably has an immunomodulatory effect that can benefit itch,” Dr. Berger said.
Several European itch centers incorporate a biopsychosocial approach to managing itch. As with chronic pain, focusing on the itch through education and support from nurses helps reduce the itch and decrease feelings of helplessness or inability to cope. Patients miss less work and report more low-itch days and improved quality of life. “So, there's a biopsychosocial aspect that probably will need to be addressed,” he said. Some U.S. centers have employed this approach in managing atopic dermatitis.