Severe Cutaneous Manifestation of Malignant Syphilis in a Patient with Behçet's Uveitis: A Case Report.

Introduction: Syphilis exhibits a wide range of clinical presentations, mimicking various systemic and ocular diseases. Ocular syphilis, in particular, manifests with multiple presentations, ranging from anterior uveitis to panuveitis, making it a potential differential diagnosis for Behçet's uveitis. Here, we present a unique case of Behçet's panuveitis that was undergoing immunomodulatory therapy and was complicated by ocular syphilis. Notably, this case also featured rare cutaneous manifestations associated with secondary syphilis, commonly known as malignant syphilis. Case Presentation: A 38-year-old Thai man with refractory end-stage Behçet's panuveitis reported a maculopapular rash accompanied by increased intraocular inflammation. The escalation of immunomodulatory therapy, intended to manage the provisional diagnosis of active ocular and cutaneous Behçet's disease, resulted in clinical deterioration, with the rash transforming into multiple noduloulcerative lesions. Despite negative serologic tests for syphilis at baseline before initiating immunomodulatory therapy, syphilis infection was eventually diagnosed following reevaluation and the observation of spirochetes in a skin biopsy specimen. The patient was treated with intravenous penicillin G, resulting in an improvement in intraocular inflammation and resolution of noduloulcerative rashes. Conclusion: Intraocular inflammation and mucocutaneous lesions in syphilis can mimic the presentation of Behçet's disease. The introduction of immunomodulatory therapy may alter the clinical picture, leading to a severe and atypical presentation. A high index of suspicion for reevaluating serologic tests or performing tissue biopsies is warranted for an accurate diagnosis.