Differential Diagnosis for Painful Penis Ulceration in a Gay Man with New Partner

Single Most Likely Diagnosis

• Primary Syphilis: This is the most likely diagnosis due to the patient's new sexual partner and the presentation of a painful penis ulceration. Primary syphilis classically presents with a single, painless chancre, but it can be painful in some cases. The recent change in sexual partner increases the risk of sexually transmitted infections (STIs), and syphilis is a common consideration in such scenarios.

Other Likely Diagnoses

• Genital Herpes: This is another common STI that can cause painful ulcers on the penis. The patient's new sexual partner and the painful nature of the ulcers make genital herpes a likely diagnosis.
• Chancroid: Caused by Haemophilus ducreyi, chancroid is characterized by one or more painful ulcers on the genitals. It is less common in developed countries but should be considered in the differential diagnosis of painful genital ulcers, especially in individuals with new or multiple sexual partners.
• Lymphogranuloma Venereum (LGV): Although LGV typically presents with a small, painless lesion that may go unnoticed, followed by lymphadenopathy, it is an important consideration in the differential diagnosis of genital ulcers in sexually active individuals, particularly those with high-risk behaviors.

Do Not Miss Diagnoses

• HIV Infection: While not directly causing ulcers, HIV infection can increase the susceptibility to other STIs and can present with various symptoms, including ulcers. Missing an HIV diagnosis can have significant consequences due to the importance of early treatment.
• Squamous Cell Carcinoma: Although rare, this type of cancer can present as an ulcerative lesion on the penis. Given the potential severity of missing a cancer diagnosis, it is crucial to consider this in the differential, especially in older individuals or those with a history of HPV infection.

Rare Diagnoses

• Behçet's Disease: A form of vasculitis that can cause genital ulcers, among other symptoms. It is rare and typically involves other systemic symptoms, but it should be considered in cases where common causes have been ruled out.
• Granuloma Inguinale (Donovanosis): Caused by Klebsiella granulomatis, this infection is characterized by painless, beefy-red ulcers on the genitals. It is rare in many parts of the world but can be seen in travelers or individuals from endemic areas.