This document provides information about Erythema Nodosum Leprosum (ENL), a type 2 reaction that occurs in patients with multibacillary leprosy with a heavy bacterial load. ENL is characterized by painful, tender red nodules on the skin that can break down and cause ulceration. It can also involve inflammation of nerves, eyes, nose, testes, joints, hands and feet. ENL is caused by an Arthus-type allergic reaction when large numbers of killed leprosy bacteria release antigens. Diagnosis involves clinical examination for skin and nerve lesions as well as slit skin smears and histopathology. Treatment focuses on corticosteroids, NSAIDs, bed rest