Fixed drug eruption (FDE) is a drug-induced, immune-mediated cutaneous reaction characterized by recurrent, well-demarcated, erythematous, and edematous lesions that reappear at the same site upon re-exposure to the offending drug. Mucosal involvement in FDE is relatively rare and clinically distinct. Oral FDE often presents differently from its cutaneous counterpart, which can complicate diagnosis. We report the case of a 35-year-old man, allergic to penicillin and metronidazole, who presented with an isolated erosion on the vestibular attached gingiva of the upper right molar region. Clinical examination revealed no lymphadenopathy or other lesions in the oral cavity, and histopathological analysis showed lichenoid inflammation. After initial clinical evaluations, the patient later revealed he had experienced similar lesions following the intake of paracetamol, including episodes affecting the head of the penis. The lesion resolved spontaneously within 15 to 21 days after discontinuation of paracetamol. Based on the patient's history, clinical presentation, and histopathological findings, a diagnosis of FDE was made. This case highlights the importance of a thorough drug history in diagnosing oral FDE, as well as the atypical clinical presentation of FDE in the oral cavity compared to its cutaneous form. Although rare, oral FDE should be considered in cases of recurrent, well-demarcated erosions associated with specific drug exposures. Early recognition and avoidance of the causative drug are essential for effective management.
Keywords: adverse event; drugs; oral diseases; oral mucosa; toxidermias.
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