Prurigo Nodularis: Chronic Itch and Emerging Therapies

Overview / Definition Prurigo nodularis (PN) is a chronic inflammatory skin disorder characterized by the presence of itchy, nodular lesions primarily on the extensor surfaces of the limbs. These nodules are typically excoriated due to the intense itching, leading to secondary skin changes and potential superinfection. PN is often considered a manifestation of chronic itch, and its management requires a multidisciplinary approach. Epidemiology Prurigo nodularis predominantly affects adults, with a higher prevalence in individuals aged 30-60 years. It is more common in women than men, and there is a noted association with various systemic conditions such as chronic kidney disease, liver disease, and HIV. Incidence: Approximately 1-2% of the general population. Prevalence: Higher in certain populations, such as those with atopic dermatitis. Associated conditions: Diabetes, hyperthyroidism, and psychiatric disorders. Pathophysiology / Mechanism The exact mechanism underlying prurigo nodularis remains unclear; however, it is believed to involve a combination of neurogenic inflammation and a dysfunctional immune response. The persistent itch-scratch cycle leads to lichenification and nodular formation. Histologically, lesions show a dense infiltrate of lymphocytes and eosinophils, along with changes in the epidermis. Neurogenic factors: Increased substance P and other neuropeptides. Immune dysregulation: Elevated levels of cytokines such as IL-31. Chronic itch: Often associated with underlying dermatologic or systemic conditions. Clinical Presentation Patients with prurigo nodularis present with multiple firm, pruritic nodules that may vary in size from a few millimeters to several centimeters. These nodules are typically located on the arms, legs, and trunk. Lesion characteristics: Flesh-colored to hyperpigmented, often excoriated. Symptoms: Intense itching that can be debilitating. Chronicity: Lesions may persist for months to years. Diagnosis / Workup The diagnosis of