Differential Diagnosis for Penile Ulcer
The patient presents with a 6mm red, oval ulcer with an indurated base on the penis, which is nontender, along with nontender lymphadenopathy of inguinal nodes. Given the patient's history of sexually transmitted infections (STIs) and high-risk behaviors, the differential diagnosis can be categorized as follows:
- Single Most Likely Diagnosis
- Syphilitic Chancre: This is the most likely diagnosis due to the description of the ulcer as having an indurated base and being nontender, which are classic characteristics of a syphilitic chancre, the primary lesion of syphilis. The patient's history of STIs and unprotected sexual encounters further supports this diagnosis.
- Other Likely Diagnoses
- Genital Herpes: Although the ulcer is described as nontender, which is less typical for genital herpes, the patient's history of STIs and the presence of an ulcer make this a possible diagnosis. Genital herpes usually presents with painful vesicles or ulcers.
- Condylomata Acuminata: These are genital warts caused by human papillomavirus (HPV). While they can appear as lesions on the penis, they are typically not described as ulcers with an indurated base. The patient's history of multiple sexual partners increases the risk for HPV.
- Do Not Miss Diagnoses
- Penile Carcinoma: Although rare and less likely given the patient's age and the acute presentation, penile cancer can present with an ulcerative lesion. It is crucial not to miss this diagnosis due to its significant implications for treatment and prognosis.
- Rare Diagnoses
- Other STIs: Such as lymphogranuloma venereum (LGV) or granuloma inguinale, which can cause ulcers but are less common in this context.
- Traumatic or Factitious Ulcer: Given the patient's history of substance use, a traumatic or self-inflicted ulcer, although unlikely, cannot be entirely ruled out without further investigation.
Each of these diagnoses should be considered in the context of the patient's full history, physical examination, and appropriate diagnostic tests, such as darkfield microscopy for syphilis, viral cultures or PCR for herpes, and biopsy for suspected malignancy.