9. Leprosy reactions

A major problem in the management of leprosy patients is the occurrence of the leprosy reactions, which are consequences of the dynamic nature of the immune response to leprosy bacteria (M. leprae) that may occur before, during, or following the completion of multidrug therapy (MDT). Reactions in leprosy constitute the main complications of the disease, which can lead to serious consequences like nerve damage and deformities. Leprosy reaction is immunologically mediated episodes of acute or subacute inflammation, which interrupts the relatively uneventful usual chronic course of diseases affecting the skin, nerves, mucous membrane, and/or other sites. Reaction may occur in any type of leprosy expect the indeterminate type. Unless promptly and adequately treated, it can result in deformity and disability. Three types of reactions recognized are classified as: (1) type 1 reaction (T1R), (2) type 2 reaction (T2R) or erythema nodosum leprosum (ENL), and (3) the Lucio phenomenon [28]. Type 1 LR (T1R) and type 2 LR (T2R) are the main causes of nerve damage and permanent disability. The LR immune-pathogenesis is currently an important research focus, as it can provide relevant targets and goals for early detection and control of this episode [29].

#### 9.1. Type 1 reaction

Type 1 reaction is associated with sudden alteration of cell-mediated immunity associated with a shift in the patient's position in the leprosy spectrum that is usually observed in borderline spectrum of the disease except very rare reports in lepromatous leprosy. If there is increase in the immunity, the shift is from borderline spectrum toward the tuberculoid pole and is called upgrading or reversal reaction. On the other hand, if there is sudden shift toward the lepromatous pole with reduction of immunity, it is called as downgrading reaction. These acute inflammatory events may accentuate the chronic course of the disease in the total clinical spectrum of the disease, usually in Borderline leprosy (BT, BB, and BL) and rare in LL. Clinical symptoms may present with complain of burning, stinging sensations in the skin lesions. They may have aches and pains in the extremities and loss of strength and/or sensory perception. Sign manifestations increased inflammation become erythematous swollen and may be tender looking like erysipelas, edema of extremities or face frequently accompanied by nerve involvement, rapid swelling with severe pain/tenderness (neuritis), and sometimes loss of nerve function [28].

#### 9.2. Type 2 reaction

Type 2 reaction is an immune complex syndrome (antigen–antibody reaction involvement complement). It is an example of type III hypersensitivity reaction by Coombs and Gell classification. T2R occurs mostly in lepromatous (LL) and sometimes in borderline lepromatous leprosy (LL), which occurs mostly during the course of antileprosy treatment. A few cases present for the first time with features of reactions before leprosy is diagnosed and treatment started. In one third of the cases, pain and swelling in the joints precede or are a component of other constitutional symptoms. In cutaneous onset, there may be appearance of skin lesions in the form of maculopapular, popular, nodular, or plaque type lesions before appearance of constitutional signs and symptoms. Fever, joint pain and constitutional sign and symptom, and skin lesion appear together. T2R without ENL is possible that the manifestations of the reactions may not be confined to the skin, and the patients may develop neuritis or systemic involvement or both, depending upon the target organs where immune complexes deposition occurs [28].
