A Case of Concurrent Behçet Disease and Erythema Multiforme in a Young Adult.

Behçet disease (BD) and erythema multiforme (EM) are rare, immune-mediated, clinically diagnosed conditions that can present with overlapping mucocutaneous findings and symptoms. We report a diagnostically challenging presentation of concurrent BD and EM characterized by oral ulcers, genital lesions, and targetoid bullous acral lesions in a 23-year-old African American man. This case highlights the risk of premature diagnostic closure and emphasizes that histopathology is supportive rather than determinative in diagnosing either of these conditions. Management required multidisciplinary input and high-dose steroids. We integrated the clinical and histopathological morphology of the patient's mucocutaneous lesions with the temporal pattern of his symptom progression to confirm a diagnosis of BD with co-occurring EM. This case underscores the importance of integrating criteria-anchored diagnosis with biopsy interpretation and reinforces discharge processes as therapeutic interventions. Notably, the patient was lost to follow-up and returned three months later with similar symptoms, highlighting the importance of discharge planning in preventing relapse.