Panniculitis: Septal vs Lobular Classification

Overview / Definition Panniculitis refers to inflammation of the subcutaneous fat layer, which can be classified into two major categories: septal panniculitis, characterized by inflammation of the septa between fat lobules, and lobular panniculitis, which involves inflammation within the fat lobules themselves. This classification helps determine the underlying etiology and guides clinical management. Epidemiology Panniculitis can occur in patients of all ages, but specific forms may have distinct demographic profiles. Common in young adults and middle-aged individuals. Gender differences exist; some forms are more prevalent in women. Geographic variations may influence prevalence rates. Pathophysiology / Mechanism The pathophysiology of panniculitis varies depending on the type: Septal Panniculitis: Involves inflammation of the connective tissue septa, often seen in conditions like erythema nodosum. The inflammatory infiltrate typically consists of lymphocytes, plasma cells, and histiocytes. Lobular Panniculitis: Characterized by inflammation within fat lobules, as seen in lobular panniculitis associated with disorders such as lupus erythematosus or nodular panniculitis. The infiltrate may include neutrophils and eosinophils. Clinical Presentation Patients with panniculitis may present with a variety of symptoms depending on the type and underlying cause: Septal Panniculitis: Commonly presents as painful, erythematous nodules, typically located on the lower extremities. Associated systemic symptoms may include fever and malaise. Often linked to underlying conditions like infections, sarcoidosis, or drug reactions. Lobular Panniculitis: May present as firm, painful nodules, often on the trunk and extremities. Less common systemic symptoms; may be associated with systemic diseases. Can lead to scarring or atrophy of the overlying skin. Diagnosis / Workup The diagnosis of panniculitis requires a thorough history, physical examination, and sometimes additional investi