A 33-year-old male presented to the emergency department with a diffuse pruritic rash that appeared several days after starting Trimethoprim/Sulfamethoxazole (TMP-SMX) for a dental infection. Initially beginning on the torso and low back, the rash spread to the palms, soles, and genitalia. Progression stopped after discontinuing TMP-SMX. He conveyed a remote history of a similar rash following use of an unknown medication, and noted that several of the current lesions arose at the same location as previous.
Skin findings typically arise within two days of exposure and then more rapidly with subsequent exposures . Characteristically, recurrent lesions appear at the same sites as prior lesions (hence “fixed”) but may arise in additional locations. The rash is classically divided into two phases: an acute phase of pruritic violaceous patches and plaques with central duskiness, followed by a residual phase of hyperpigmentation that can last several months. The sulfonamide moiety of TMP-SMX is a common cause of FDE . Management of FDE anchors on identification and discontinuation of the causative agent. The majority of cases involve five or fewer lesions, however generalized or bullous cases (> 10% total body surface area, or involvement of 3 or more anatomic sites) , may require aggressive wound care and carry a mortality rate up to 22% . Topical or systemic steroids are common adjuncts and there is limited evidence suggesting the utility of systemic cyclosporine for severe cases . Patients need to be carefully advised on the risks of specific medication use and can expect a gradual resolution of lesions over the coming months.
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