Secukinumab-Induced Delayed Behçet-Like Reaction in a Patient with Plaque Psoriasis: A Case Report.

Purpose: This report presents a rare paradoxical reaction manifesting as Behçet's-like features, which developed three months following the initiation of secukinumab therapy for psoriasis. Patients and Methods: A 38-year-old female with a 30-year history of plaque psoriasis achieved significant remission of psoriatic lesions following seven doses of secukinumab (cumulative dose: 2100 mg). However, she subsequently developed systemic adverse events, including pharyngodynia, painful tonsillar and genital ulcers, folliculitis-like papules on the trunk and extremities, and erythema nodosum-like lesions on the extensor surfaces of both lower limbs. Laboratory tests, including bacterial, viral, and fungal cultures, excluded infectious etiologies. Histopathological examination of a skin biopsy demonstrated superficial and deep perivascular and interstitial inflammation with dense infiltration of lymphocytes, neutrophils, and eosinophils. Consequently, a diagnosis of secukinumab-induced Behçet's-like syndrome was established, as the patient did not fully meet the International Criteria for Behçet's Disease (ICBD). Secukinumab was immediately discontinued, and the patient was initiated on thalidomide (50 mg, three times daily) and colchicine (0.5 mg, twice daily). Results: Two weeks after treatment initiation, oral and genital ulcers resolved. Folliculitis-like papules and erythema nodosum-like lesions regressed significantly, leaving only residual post-inflammatory hyperpigmentation. The patient was subsequently switched to ustekinumab maintenance therapy at a standard dosage. Psoriasis remained well-controlled, with no recurrence of Behçet's-like manifestations during a 4-year follow-up period. Conclusion: This report underscores the critical need for vigilant patient monitoring during anti-IL-17 therapy to detect such uncommon yet clinically significant paradoxical reactions. Furthermore, precise characterization of the onset timing of such adverse events is crucial, as it enables clinicians to implement timely preventive measures, mitigate risks, and rapidly identify emerging adverse reactions.