Differential Diagnosis for a Young Adult Male with a Painless Ulcer on the Penis

• Single most likely diagnosis:
  • Primary Syphilis: This is the most likely diagnosis given the presentation of a painless ulcer (chancre) on the penis following unprotected sex with a new partner, along with enlarged and non-tender lymph nodes. Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum, and its primary stage is characterized by the appearance of a chancre, typically within 3 weeks of exposure.
• Other Likely diagnoses:
  • Genital Herpes: Although typically painful, some cases of genital herpes can present with minimal discomfort. The presence of multiple ulcers and a history of unprotected sex could suggest this diagnosis.
  • Lymphogranuloma Venereum (LGV): This is another sexually transmitted infection that can cause ulcerative lesions and lymphadenopathy. However, the ulcers in LGV are often painful and may go unnoticed, with the primary symptom being significant lymph node enlargement.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed):
  • HIV Infection: While not directly causing ulcers, HIV can increase susceptibility to other sexually transmitted infections, including those that cause ulcers. Early diagnosis of HIV is crucial for treatment and prevention of complications.
  • Cancer (e.g., Squamous Cell Carcinoma): Although rare in young adults, any persistent or atypical ulceration should prompt consideration of malignancy to ensure early detection and treatment.
• Rare diagnoses:
  • Chancroid: Caused by Haemophilus ducreyi, chancroid presents with one or more painful ulcers and is typically accompanied by tender lymphadenopathy, making it less likely in this scenario due to the painless nature of the ulcer.
  • Granuloma Inguinale (Donovanosis): This is a rare sexually transmitted infection characterized by ulcerative lesions without lymphadenopathy, which can be painless but typically bleed easily on contact.