DIAGNOSTIC CHALLENGE: VIRCHOWIAN LEPROSY WITH TYPE 2 LEPROSY REACTION MIMICKING LYMPH NODE TUBERCULOSIS ‒ CASE REPORT

Leprosy is an infectious disease caused by Mycobacterium leprae, an acid-fast bacillus (AFB). It presents paucibacillary and multibacillary forms, the latter including virchowian leprosy, the most contagious form, with extensive skin and peripheral nervous system involvement. Due to the host immune response to multibacillary infections, type 2 leprosy reactions arise, which are immune complex–mediated inflammatory conditions, classically manifesting as erythema nodosum leprosum. This report aims to describe an unusual systemic type 2 leprosy reaction in an immunocompetent patient with virchowian leprosy. A 47-year-old male painter, cannabis and alcohol user, immunocompetent, presented with right inguinal lymphadenopathy for three weeks. Lymph node biopsy revealed aggregates of foamy histiocytes, and Ziehl-Neelsen staining was positive for AFB. The patient was started on treatment for lymph node tuberculosis and subsequently developed facial nodules, nodules on the elbows, and infiltrated urticarial erythematous plaques on the face and upper limbs, progressing to bullous lesions associated with erosions of the lower lip mucosa, marked conjunctival hyperemia with foreign body sensation, and fever of 38°C. Skin biopsy showed a subepidermal cleft with neutrophils and a lymphohistiocytic infiltrate. Ziehl-Neelsen staining revealed fragmented AFB within histiocytes, and immunofluorescence showed linear IgA deposits and focal C3c deposits along the basement membrane, consistent with a type III hypersensitivity pattern. Type 2 leprosy reaction, or erythema nodosum leprosum, represents a type III hypersensitivity reaction mediated by circulating immune complex deposition, mainly IgM and IgG. The bullous clinical pattern is rare but reflects severe inflammatory tissue damage. Identification of IgA and C3c deposits in the basement membrane is uncommon in type III hypersensitivity reactions and more frequently observed in autoimmune diseases; however, such findings may occur in exuberant or atypical cases. In this case, the reaction was triggered by an initial incorrect diagnosis of lymph node tuberculosis, which can mimic multibacillary forms of leprosy, resulting in inappropriate treatment and delayed recognition of the correct etiology.