Type 2 leprosy reaction presenting as a monoarthritis post multidrug therapy

Type 2 leprosy reaction, or erythema nodosum leprosum (ENL), involves a complex interaction between the host's immune system and Mycobacterium leprae. It may occur before, during, or after treatment and have a variable clinical presentation involving different body systems, such as skin, osteoarticular, kidneys, and others. Thus, the differential diagnosis, depending on its clinical presentation, can be broad and challenging. The authors report a case of a severe monoarthritis during a type 2 reaction after the multidrug therapy (MDT) was discharged and the investigation of the differential diagnoses.