[A Case of Secondary Syphilis Mimicking a Penile Cancer with Lymph Node Metastases].

A 42-year-oldman visited our hospital because of gradually worsening penile swelling over 3 weeks. A hard mass on the glans was palpated; however, we were unable to observe it due to severe phimosis. Magnetic resonance imaging of the pelvis revealed enlargement of glans and swelling of bilateral inguinal lymph nodes as both showed a low signal intensity on T2-weightedimaging, a high signal intensity on diffusion-weighted imaging, and a low signal intensity on the apparent diffusion coefficient map. Fluorine- 18-deoxyglucose (FDG) positron emission tomography showed FDG uptake at the external iliac, common iliac, obturator, and cervical lymph nodes besides the glans and inguinal lymph nodes. Although his serum squamous cell carcinoma antigen level was within the normal range, his soluble interleukin-2 receptor concentration was elevated to 2,290 U/ml. Therefore, we diagnosed these lesions as penile cancer with multiple lymph node metastases, with a possible differential diagnosis of malignant lymphoma. We planned a penile needle biopsy; however, the rapid plasma reagin test and treponema pallidum hemagglutination test, which were performed during the preoperative examination, were positive and led to a diagnosis of secondary syphilis. The patient was treated with oral amoxicillin at 1,500 mg/day for 8 weeks. The penile and lymph node swelling subsided after starting medication.