A Rare Case of Lichen Planus Mimicking Secondary Syphilis: The Great Imitator Unveiled.

Secondary syphilis, often referred to as "The Great Imitator," is a diagnostic challenge due to its ability to mimic a range of dermatological conditions. Accurate differentiation is critical, particularly in patients with immunocompromised states, as misdiagnosis can lead to inappropriate management. This case highlights a unique presentation of lichen planus resembling secondary syphilis. A 68-year-old female undergoing chemotherapy for breast cancer presented with asymptomatic pink, scaly plaques on her palms and mucosal patches on her tongue. Concern for secondary syphilis prompted a serologic workup, including a rapid plasma reagin (RPR) test, which was non-reactive. Physical examination revealed no cervical, axillary, or inguinal lymphadenopathy, a hallmark feature of secondary syphilis. A 3 mm punch biopsy of the palmar lesions showed findings characteristic of lichen planus, including hyperkeratosis, hypergranulosis, and a band-like lymphocytic infiltrate. Special stains for spirochetes were negative. The patient was treated with apremilast (Otezla®) 30 mg orally twice daily and clobetasol 0.05% cream applied twice daily. After two weeks, significant improvement in the lesions was observed. This case underscores the diagnostic complexities of lichen planus mimicking secondary syphilis. Secondary syphilis commonly presents with systemic symptoms and lymphadenopathy, which were absent in this patient. Histopathologic confirmation played a pivotal role in differentiating the two conditions. This case adds to the growing body of knowledge on atypical presentations of lichen planus in immunocompromised patients. Clinicians should maintain a broad differential diagnosis for palmoplantar and mucosal lesions. Histopathology remains a cornerstone in confirming the diagnosis and guiding appropriate management.