# A Case of Anatopic Phenomenon in Dapsone Hypersensitivity Syndrome

## TL;DR

A 67-year-old woman developed dapsone hypersensitivity syndrome during leprosy treatment, showing a rare anatopic response where inflammation avoided existing skin lesions.

## Contribution

This paper documents a rare anatopic response in dapsone hypersensitivity syndrome and explores its underlying pathogenic mechanisms.

## Key findings

- A patient with leprosy developed dapsone hypersensitivity syndrome with anatopic response, avoiding pre-existing hypopigmented patches.
- Discontinuation of dapsone and treatment with dexamethasone resolved the hypersensitivity reaction.
- The case highlights the under-recognized anatopic phenomenon in dermatological drug reactions.

## Abstract

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.