Most Likely Diagnosis: Gonorrhea
The most likely diagnosis is gonorrhea (Option C), given the classic presentation of greenish penile discharge combined with dysuria, urinary frequency/urgency, and rectal discomfort in a sexually active male patient. 1, 2
Clinical Reasoning
Key Diagnostic Features
The combination of symptoms strongly points toward gonococcal infection:
- Greenish/purulent penile discharge is the hallmark sign of gonorrhea in men, distinguishing it from other urogenital infections 1, 3
- Dysuria with urinary frequency and urgency represents urethritis, which is the most common manifestation of gonorrhea in males 1, 2
- Rectal discomfort suggests anorectal gonococcal infection, which can occur through receptive anal intercourse 1, 2
Why Not the Other Options
Complicated UTI (Option A) is unlikely because:
- UTIs in young males are uncommon without anatomical abnormalities or catheterization 4
- The presence of greenish penile discharge is not characteristic of simple bacterial UTI 4
- Rectal involvement would be atypical for UTI 4
Syphilis (Option B) is unlikely because:
- Primary syphilis presents with painless genital ulcers (chancres), not discharge 5, 3
- The symptom complex described does not match syphilitic presentations 5
Epididymitis (Option D) is unlikely because:
- Epididymitis typically presents with scrotal pain and swelling, which are not mentioned 6
- While gonorrhea can cause epididymitis, the primary presentation here is urethritis with discharge 6
Diagnostic Approach
Recommended testing includes: 6, 1, 3
- Urethral swab or first-void urine for nucleic acid amplification testing (NAAT) with sensitivity 86.1-100% and specificity 97.1-100% 3
- Rectal swab for NAAT given the rectal symptoms 1, 2
- Testing for co-infection with Chlamydia trachomatis, as coinfection is common 6, 1, 3
- Screening for other STIs including syphilis and HIV, as recommended for all newly diagnosed STD patients 6, 1
Clinical Pitfalls to Avoid
- Do not dismiss extragenital symptoms: Approximately 53-100% of extragenital gonorrhea infections (pharyngeal, rectal) may be asymptomatic or minimally symptomatic, but this patient has rectal discomfort 3
- Always test for chlamydia concurrently: Coinfection rates are high enough that dual testing is standard practice 6, 1
- Partner notification is essential: All sexual partners within the preceding 60 days should be evaluated and treated 6