What is a fixed drug eruption? And why does it keep coming back?

Your Case:

A previously healthy, 8 year-old Hispanic boy presents to the ED with a recurrent rash on his right posterior thigh. The involved area always becomes “infected” whenever the patient develops a fever, and this is the 3^rd and most severe episode.

1^st episode– 2 years ago, the family was still living in Mexico, and at that time the rash was diagnosed as an insect bite. Mom empirically treated with topical antibiotics. Within a week, the lesion resolved, but the patient was left with a small, dark, discolored area in its place.

2^nd episode – 1 year ago, he had an episode of fever and diarrhea with a red, pruritic lesion on right posterior thigh. Again, a topical antibiotic was placed on the area. After resolution of the illness, the redness improved, but he was left with an even larger dark discoloration at the site.

3^rd episode– 5 days ago, the patient developed fever and URI symptoms. On Day 2 of illness, a red, pruritic, blistering area started developing on right posterior thigh. He was diagnosed in ED with cellulitis and sent home with trimethoprim/sulfamethoxazole. On Day 3, the fever and URI symptoms began to resolve, but the rash was progressing despite compliance with the antibiotic.

Today, the rash looks like this:

Physical Exam– Well appearing, afebrile. Lesion as shown above, non-tender, negative Nikolsky sign, no fluctuance, no mucous membrane involvement, no other skin lesions.

Labs– CBC/CRP/CMP/LFT- all normal

What you need to know

• The most reliable and characteristic finding of a fixed drug eruption is the recurrence of the lesion at the same site, which can be anywhere on the skin or mucosa.
• History-taking is key
• Trimethoprim-sulfamethoxazole and acetaminophen are commonly implicated in fixed drug eruptions.
• The mainstay of treatment is to prevent recurrence of the eruption by avoiding the offending drug

References

Cossey, M. et al. Visual Diagnosis:8-Year-Old Boy With Recurrent Rash. Pediatrics in Review 2000;36;4

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