Prurigo nodularis is a chronic condition of uncertain etiology. Although exact prevalence is unknown, it is most commonly seen in patients aged 45 years and older and seems to be more common in women and in people of color. Patients present with one or more (usually multiple) discrete, severely pruritic nodules that mostly appear on the extensor surfaces of extremities and anterior areas of the thighs and legs. The lesions are rarely seen on the face. The lesions are triggered by repetitive rubbing or scratching of discrete areas of the skin. Pruritus is described as severe and distressing and can become worse with heat, sweating, or irritation from friction. It may alternatively be induced by repetitive picking or rubbing of nonpruritic skin.

Prurigo nodularis may be secondary to skin conditions associated with pruritus, such as atopic dermatitis and xerosis, as well as systemic conditions associated with generalized pruritus without a primary skin rash, such as psychiatric conditions, eating disorders, HIV infection, iron-deficiency anemia, diabetes mellitus, gluten enteropathy, thyroid disease, renal or hepatic impairment, malignancies, and others. In most cases, the etiology of pruritus is unknown. Studies have suggested that prurigo nodularis may be a form of subclinical small fiber neuropathy and that Th2 cytokines play an important role in its pathogenesis.

Lesions are firm dome-shaped, smooth-topped, or crusted nodules. Their size ranges from several millimeters to 1-2 cm, and they often enlarge slowly over time. Lichenification of the lesions is often not present.

Patients with this disorder may have an increased risk of various general medical conditions.