Generalized itching, often without a rash, can be one of the most frustrating problems for a dermatologist to encounter in clinic due to the variable presentation and wide-ranging etiologies at play. In this session, David E. Cohen, MD, MPH, reviewed the etiology and pathogenesis of itching and simplified the potential work-up and treatment options for patients with chronic itch. Beginning with epidemiology, Dr Cohen reminded the audience that chronic itching (>6 weeks) is very common, with a lifetime prevalence of 8% to 25.5%. Elderly and African American patients are at higher risk of chronic itching, while individuals over the age of 60 years with a history of liver disease and diffuse itch of less than 12 months duration are at higher risk of having an underlying malignancy. Initial evaluation should focus on whether there is concomitant inflamed or diseased skin, as this points to a primary dermatologic disorder as the cause of itching. Along with a thorough medical history and physical exam, a complete review of systems is important for all patients presenting with chronic itching. Dr Cohen recommended checking a complete blood count with differential, complete metabolic panel, thyroid function tests, and diabetes screening as an initial lab workup.

Dr Cohen quickly reviewed the dermatologic diseases associated with itching, such as atopic dermatitis, psoriasis, contact dermatitis, and scabies, and reminded the audience that some of these disorders often coexist. Dr Cohen presented a case report of concomitant atopic dermatitis, ichthyosis vulgaris, and allergic contact dermatitis to highlight this point. Dr Cohen also dove into the recent breakthroughs in the understanding of the mechanism of itch, with immune signaling molecules IL-4, IL-13, IL-31, and thymic stromal lymphopoietin playing key roles in mediating itch signaling. Moving on to systemic causes of itch, Dr Cohen discussed itching related to chronic kidney disease, cholestasis, diabetes, hyper- and hypothyroidism, malignancies, and chronic infections. Neuropathic causes of itch are often encountered in dermatology clinics, such as brachioradial pruritus, notalgia paresthetica, scalp dysesthesia, and anogenital pruritus.

To conclude, Dr Cohen reviewed the various treatment options for chronic itching: topical and localized therapies including topical corticosteroids, calcineurin inhibitors, capsaicin, pramoxine- and lidocaine-containing creams, phosphodiesterase inhibitors, cannabinoids, doxepin, and even localized botulinum toxin injections. Dr Cohen discussed indications for systemic immunosuppression for chronic pruritus of unknown origin (CPUO). Methotrexate, cyclosporine, or biologics such as dupilumab can be effective for CPUO with Th2 differentiation, or when patients have increased eosinophils and elevated IgE. Gabapentin and pregabalin can be effective for CPUO without Th2 differentiation. Opioid receptor modulators, such as naltrexone, difelikefalin, and butorphanol are options for intractable itching that is unresponsive to other systemic treatments. Gastrointestinal distress, drowsiness, and risk of dependence with long-term use are potential side effects.