A 90-year-old patient was brought to the emergency department with a 3-day history of a progressively worsening erythematous rash on the trunk and abdomen. She had been taking valacyclovir and metamizol for 4 days after developing herpes zoster on the upper left flank prior to onset of symptoms. Physical examination revealed a maculopapular erythematous rash over the trunk, abdomen and proximal extremities. The rash spared crusts and erosions that followed a dermatomal distribution suggestive of herpes zoster infection ( Figure 1A ). On dermoscopy, individual lesions were composed of a central reddish crust surrounded by a white halo with shiny white lines, and perilesional erythema with linear and dotted vessels ( Figure 1B ).
A skin biopsy was performed, including a crust, rash, and unaffected skin. The biopsy revealed three histopathologically distinct zones. In the center of the biopsy, there was an unspecific erosion that tested negative for herpes virus 1 and 2. The periphery of the biopsy showed a moderate dermal inflammatory infiltrate with eosinophils ( Figures 1, C and D ). In between those areas, there was a zone with minimal changes corresponding to the spared skin. A diagnosis of acute drug eruption with reverse isotopic phenomenon over healing herpes zoster lesions was made. The rash disappeared shortly after discontinuing all medication and receiving a short course of systemic corticosteroids. The patient declined further testing, including drug patch testing.
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