Pruritus (itch) is the unpleasant sensation of the skin that results in an urge to scratch. It is a major symptom of many cutaneous and systemic diseases. Pruritus can range from mild to severe and may be intermittent or chronic (lasting longer than 6 weeks). Pruritus can have a significant impact on health-related quality of life (HRQOL), and has been associated with depression, decreased sleep quality, and a negative impact on most quality of life categories.1 The authors of a case-control study of patients with chronic pruritus observed that the impact of chronic pruritus on HRQOL may be similar to that of chronic pain.2 Pruritus has multiple etiologies in patients with and without underlying skin disease. The International Forum for the Study of Itch recently published a clinical classification of pruritus 3 in which they proposed six categories for pruritus based on the underlying origin:
Dermatological: Pruritus associated with diseases of the skin, including diseases which feature prominent pruritus such as atopic dermatitis, allergic contact dermatitis, xerotic dermatitis, lichen simplex chronicus, lichen planus, scabies, and urticaria. These diseases typically have characteristic skin findings.
Systemic: Pruritus associated with diseases in organs other than the skin, such as the liver, kidneys, hematopoietic system, malignancy, nutrient deficiency, medications, or illicit substances with pruritus as a side-effect.
Neurological: Pruritus associated with damage to nerve fibers from diseases or disorders of the central nervous system (e.g., brain and spinal cord injury, brain tumors) or peripheral nervous system (e.g., damage from diabetes mellitus or herpes zoster, narrowing of bony foramina from osteoarthritis).
Psychogenic/Psychosomatic: Pruritus associated with psychiatric disorders and defined as itch not related to dermatologic or systemic causes.
Mixed: Pruritus from combinations of categories 1–4.
Other: Pruritus of undetermined origin.
Typically, the pruritus in categories 2–6 is associated with no primary skin lesions. However, secondary lesions from scratching or rubbing, such as excoriations (Figure 25-1), prurigo nodularis (Figure 25-2), or lichenification (Figure 25-3) can be seen. Additionally, a patient's pruritus may span multiple categories. For example, pruritus in the elderly may occur due to decreased function of the stratum corneum, including reduced lipid production, compounded by polypharmacy, low iron levels, or neuropathy from diabetes mellitus. It is important to determine the etiology of chronic pruritus, because it can be an early symptom of the diseases in categories 2–4. Table 25-1 contains information about selected diseases that are associated with chronic pruritus starting with the most likely diseases.
Excoriations with post inflammatory hyperpigmentation on back of patient with no underlying skin disease.
Purigo nodularis. Grouped excoriated papules secondary to scratching.
Lichenification of skin due to chronic scratching.