A Case of Anatopic Phenomenon in Dapsone Hypersensitivity Syndrome

We report a case of a 67-year-old woman on multidrug therapy for borderline lepromatous leprosy who developed dapsone hypersensitivity syndrome (DHS). She presented with fever and red pruritic rash over her face, neck, trunk and upper limbs, with distinct sparing of hypopigmented leprosy patches on her trunk. Laboratory findings showed anemia, elevated white blood cell count and liver function abnormalities. Upon discontinuation of dapsone and initiation of intravenous dexamethasone, the reaction subsided. This case report describes anatopic response, a phenomenon where a cutaneous infection modifies the inflammatory response of a secondary inflammatory dermatoses at the same location. We further elucidate the pathogenic mechanisms implicated in anatopic response, a phenomenon not commonly documented in the literature.