Pruritus, or itch, is a sensation that leads to scratching. It can be acute or chronic (lasting more than 6 weeks), localized or generalized, and is broadly categorized neuroanatomically as pruritoceptive, neuropathic, neurogenic, or psychogenic. Itch is the most common symptom in many inflammatory skin diseases (e.g., atopic dermatitis, contact dermatitis, and psoriasis) and infectious skin diseases (e.g., chickenpox), but it may also be associated with systemic diseases (e.g., chronic renal failure, HIV, cutaneous T-cell lymphoma) or simply xerosis. Because it is a subjective experience that is associated with a variety of conditions, it is difficult to estimate the incidence and prevalence of pruritus.

Pruritus provokes patients to scratch or rub their skin, which serves to potentiate the vicious scratch-itch cycle. Consequently, areas of itching may eventually manifest as areas of bleeding, excoriations, ulcerations, and crusts. Further scratching results in lichenification with changes in skin pigmentation as well as scar formation. Chronic pruritus may lead to hyperpigmented plaques and excoriated nodules resembling prurigo nodularis (Figs. 35-1, 35-2, 35-3) (Table 35-1).

Pruritus is a subjective perception described by the patient. In order to properly treat pruritus, the underlying cause must be elicited through a thorough history, physical examination, and a diagnostic workup. History should include location, onset, timing, duration, and character of the itch, as well as alleviating/aggravating factors and patient characteristics (e.g., age, medications, allergies, and signs of systemic disease). In addition to careful examination of the skin, nails, scalp, hair, and mucous membranes, a physical examination should also include palpation of lymph nodes, thyroid gland, and abdomen. Initial laboratory investigations should include a complete blood count with differential, as well as liver, renal, and thyroid function tests and urinalysis. Additional tests, such as anemia analysis, HIV, chest x-ray, and abdominal ultrasound, may also be necessary (Table 35-2).