Sarcoidosis: Cutaneous Manifestations

Overview / Definition Sarcoidosis is a systemic inflammatory disease characterized by the formation of noncaseating granulomas in various organs, with the skin being one of the frequently affected sites. The exact etiology remains unclear, but it is thought to involve a complex interaction between genetic predisposition and environmental factors. Epidemiology Sarcoidosis has a variable incidence across different populations and geographical regions. It is more prevalent in individuals of African descent and those aged between 20 and 40 years. The estimated prevalence in the United States is approximately 10 to 40 cases per 100,000 people. Higher prevalence among women than men. Familial clustering suggests a genetic component. Environmental exposures (e.g., silica, beryllium) may increase risk. Pathophysiology / Mechanism The pathophysiology of sarcoidosis involves an exaggerated immune response to an unknown antigen, leading to granuloma formation. The granulomas consist of macrophages, epithelioid cells, multinucleated giant cells, and T lymphocytes. Cytokines such as tumor necrosis factor-alpha (TNF-α) play a crucial role in granuloma maintenance. Granuloma formation is primarily mediated by CD4+ T cells. Type 1 helper T (Th1) cell response is characteristic of the disease. Increased levels of angiotensin-converting enzyme (ACE) may be noted. Clinical Presentation Cutaneous manifestations of sarcoidosis are diverse and may mimic other dermatological conditions. Approximately 20-30% of patients with sarcoidosis develop skin lesions, which can present in various forms: Maculopapular eruptions: Often red-brown, raised lesions, frequently found on the extremities and trunk. Plaque sarcoidosis: Well-defined, erythematous plaques that can be mistaken for psoriasis. Lupus pernio: A chronic form characterized by indurated, violaceous plaques, commonly on the face. Scar sarcoidosis: Lesions that develop in previously injured skin. Subcutaneous nodules: Soft, mobile nodule