Definition:

Reactional states of leprosy are expressions of immunological disturbance and are generally divided into two variants: type 1 (Jopling's type I or reversal reaction) and type 2 (Jopling's type II reaction). Erythema Nodosum Leprosum (ENL), the main symptom of a type-2 reaction in leprosy, is caused by a humoral immune response to Mycobacterium leprae. Patients with ENL become acutely sick with fever, malaise, and crops of painful erythematous nodules. Inflammation often affects other systems causing iritis, neuritis, myositis, lymphadenitis, arthritis, dactylitis, and orchitis.