Practical guide for the diagnosis and treatment of localized and generalized cutaneous pruritus (chronic itch with no underlying pruritic dermatosis)

Itch, also known as pruritus, is one of the most prevalent symptoms observed in dermatological practices. Itch frequently arises from primary pruritic dermatoses, although it may also manifest in the absence of a primary pruritic skin rash. The latter itchy condition is referred to as "cutaneous pruritus" in the Japanese guidelines published in 2020. Cutaneous pruritus can be classified into two categories based on its distribution: localized cutaneous pruritus and generalized cutaneous pruritus. Localized cutaneous pruritus is indicative of a neuropathic cause, whereas generalized cutaneous pruritus suggests underlying systemic disease(s), drug-induced itch, psychogenic itch (also known as functional itch disorder), or chronic pruritus of unknown origin (CPUO). Systemic diseases associated with cutaneous pruritus include disorders of iron metabolism, chronic kidney disease, chronic liver disease (especially cholestasis), endocrine/metabolic diseases, hematological disorders, and malignant solid tumors. CPUO is a term used to describe chronic itch that is often generalized and for which no underlying cause can be identified despite a comprehensive and careful diagnostic workup. A variety of treatment approaches are available for cutaneous pruritus, including device-based physical therapies (such as phototherapy) and medications that act on the itch-perception processing pathway from the skin, peripheral sensory nerves, the spinal cord, to the brain. This review presents an overview of the current knowledge regarding cutaneous pruritus, from its underlying pathophysiologic mechanisms to the diagnostic procedures and treatment approaches that are currently available.