A Case of Nonpigmenting Fixed Drug Eruption by Pseudoephedrine

Abstract

A 35-year-old man presented with a skin eruption that developed two days after taking medication for a cold. Over the past three years, cold treatments had caused erythema on his buttocks and thighs, which resolved without hyperpigmentation. However, he now experienced erythema accompanied by heat and mild pain in his groin, buttocks, thighs, popliteal fossae, and both sides of his hands. Histopathological analysis revealed minimal changes in the epidermis and lymphocytic inltration around blood vessels in the supercial dermis. Patch testing on the affected skin area using the three drugs he had taken yielded a positive result for the combination tablet of fexofenadine hydrochloride and pseudoephedrine hydrochloride, and a negative result for fexofenadine alone. Oral provocation testing with fexofenadine alone was also negative. We diagnosed the patient with a nonpigmenting xed drug eruption caused by pseudoephedrine hydrochloride in the combination tablet. In nonpigmenting xed drug eruption, large erythematous lesions appear in intertriginous areas, recur in the same location, and resolve within 2 to 3 weeks without hyperpigmentation. Due to its presentation in intertriginous areas, it may initially be diagnosed as an intertriginous drug eruption. There is some overlap between nonpigmenting xed drug eruption and intertriginous drug eruption, necessitating further investigation. The present case represents the fth report of nonpigmenting xed drug eruption caused by pseudoephedrine in Japan. Patch tests were performed in three of these cases, including ours, and all showed positive results, suggesting that patch testing is a useful diagnostic tool. For eruptions in intertriginous areas, we recommend performing patch tests on both affected and unaffected skin areas to examine the possibility of nonpigmenting xed drug eruption. Skin Research, 23 : 222-228, 2024