Pruritus at a Glance
- Pruritus is the predominant symptom of skin disease.
- May originate in the skin or nervous system.
- Clinical classification of itch includes:
- pruritus on diseased (inflamed) skin
- pruritus on nondiseased (noninflamed) skin
- pruritus presenting with severe chronic secondary scratch lesions
- Chronic itch consists of multidimensional phenomena including sensory, emotional, and cognitive components.
- Central and peripheral mediators in humans include histamine, proteinases, opiates, substance P, nerve growth factor, interleukins, and prostaglandins.
- Treatment should address the multifactorial nature of pruritus including central pathways and peripheral mediators.
Pruritus (itching) is the predominant symptom of skin disease and can best be defined as a sensation that leads to a desire to scratch. All human beings experience this sensation in the course of their lifetime; therefore, it is important to make a distinction between acute itch, which is of a limited period of time ranging from seconds to a week such as the itch related to acute insect bite reaction, and chronic itch, which lasts for months and is the focus of this chapter.1 Chronic itch is a multidimensional phenomenon consisting of sensory, emotional, and cognitive components. In most cases, chronic itch results from interaction of the brain-skin axis. Although itch and pain are separate and distinct sensations, itch has many similarities to pain.2,3 Both itch and pain are unpleasant sensory experiences, follow similar neural pathways, and can severely impair patients’ quality of life. However, the behavioral response patterns differ—pain elicits a reflex withdrawal, whereas itch leads to a scratch reflex.
The limited understanding of itch results from the subjective nature of itching, the absence of specific and sensitive investigational methods to study the neuropathophysiology and molecular basis of itch in humans, the lack of convincing animal models and incomplete knowledge of pharmacologic mediators of pruritus. However, significant progress has been made in the past decade with the discovery of new neural pathways (both histaminergic and nonhistaminergic) as well as novel receptors in humans and animals. The concept that itch is transmitted to the central nervous system (CNS) and processed in the brain should lead to new approaches to antipruritic therapy.4
Itch is a symptom rather than a specific disease entity; therefore, epidemiologic data for itch are limited. Nevertheless, itch has been found to be the dominant skin complaint among all age groups.5 In a large cross-sectional study in Norway, the prevalence of pruritus was approximately 8% among adults.6 Itch is a primary symptom in a diverse range of skin diseases as well as in systemic diseases. The prevalence of pruritus in different dermatologic and systemic diseases is outlined in Tables 103-1 and 103-2.
Table 103-1 Prevalence of Itch in Skin Disorders and Infectious Skin Diseases ||Download (.pdf)
Table 103-1 Prevalence of Itch in Skin Disorders and Infectious Skin Diseases
Estimated Prevalence of Pruritus