Nummular Dermatitis: Differential and Management

Overview / Definition Nummular dermatitis is a type of eczema that presents as round, coin-shaped lesions on the skin. These lesions are typically itchy, erythematous, and can become crusted or scaly. Nummular dermatitis can be particularly challenging to manage due to its chronic nature and tendency to relapse. Epidemiology Nummular dermatitis is more prevalent in adults, although it can occur at any age. The condition is seen more often in individuals with a history of atopy, including asthma and allergic rhinitis. Key epidemiological points include: Incidence is higher in males than females. Often occurs in the winter months due to dry skin conditions. Commonly affects patients with a personal or family history of atopic conditions. Pathophysiology / Mechanism The exact pathophysiology of nummular dermatitis remains unclear, but it is believed to involve: Disruption of the skin barrier function leading to increased transepidermal water loss. Immune dysregulation resulting in an inflammatory response, particularly involving T-helper cell type 2 (Th2) pathways. Increased susceptibility to irritants and allergens due to compromised skin integrity. Clinical Presentation Patients with nummular dermatitis typically present with: Coin-shaped plaques that are well-defined and can vary in size from a few millimeters to several centimeters. Lesions are usually located on the extremities, trunk, and sometimes the hands and feet. Intense pruritus, which can lead to excoriation and secondary infections. Chronic lesions may display scaling, crusting, and lichenification. Diagnosis / Workup The diagnosis of nummular dermatitis is primarily clinical, based on the characteristic appearance of the lesions. However, a thorough workup may include: Clinical history to identify potential triggers, including allergens and irritants. Physical examination to assess the distribution and morphology of lesions. Patch testing if allergic contact dermatitis is suspected. Skin scraping to rule