What is the differential diagnosis for an adult presenting with penile shaft swelling and purulent discharge?

Differential Diagnosis for Penile Shaft Swelling with Purulent Discharge

The most critical differential diagnoses to consider are gonococcal urethritis, nongonococcal urethritis (primarily chlamydial), penile abscess, and less commonly median raphe cyst infection or parameatal duct infection.

Primary Infectious Etiologies

Sexually Transmitted Urethritis

The two most important bacterial pathogens causing purulent discharge are Neisseria gonorrhoeae and Chlamydia trachomatis, which together account for the majority of urethritis cases in men 1.

• Gonococcal urethritis presents with purulent discharge and is confirmed by Gram stain showing Gram-negative intracellular diplococci 1
• Nongonococcal urethritis (NGU) is characterized by mucopurulent discharge when Gram-negative intracellular organisms cannot be identified on Gram stain 1
• C. trachomatis causes 23-55% of NGU cases, with prevalence varying by age group 1
• Ureaplasma urealyticum accounts for 20-40% of NGU cases 1, 2
• Trichomonas vaginalis causes 2-5% of NGU cases and can rarely cause penile shaft infection along the median raphe 1, 3
• Mycoplasma genitalium is implicated in approximately one-third of nonchlamydial NGU cases 1, 2

Penile Shaft Abscess and Cellulitis

Penile shaft abscess is a critical diagnosis that can rapidly progress and requires urgent surgical intervention 4.

• Streptococcus intermedius has been documented as a causative organism following trauma from sexual activity, with abscess formation and rupture occurring within 24 hours 4
• Enteric organisms may cause infection, particularly in men over 35 years or those practicing insertive anal intercourse 2
• Secondary infection of developmental abnormalities (median raphe canals, parameatal ducts) can produce swelling, tenderness, and purulent discharge 5, 6

Epididymitis with Extension

Sexually transmitted epididymitis can present with swelling extending to the penile shaft 7.

• Caused by N. gonorrhoeae or C. trachomatis in sexually active men under 35 years 7
• Enteric organisms are more common in men over 35 years 7

Non-Infectious Etiologies

Traumatic Lymphatic Obstruction

• Penis friction edema results from vigorous sexual activity causing lymphatic drainage disruption 8
• Presents as local or total penile swelling without purulent discharge unless secondarily infected 8
• This diagnosis is made by exclusion after ruling out infectious and obstructive causes 8

Developmental Anomalies with Secondary Infection

• Median raphe canals are epithelial-lined structures along the ventral penis that can become secondarily infected, producing swelling and purulent discharge 5
• Parameatal ducts are rare embryologic remnants around the urethral meatus that can cause persistent irritation and purulent discharge 6
• These structures do not communicate with the urethra and require surgical excision if unresponsive to antibiotics 5, 6

Emergency Conditions to Rule Out

Always exclude these surgical emergencies first:

• Penile fracture: Suspect if there is history of cracking/snapping sound during intercourse, immediate detumescence, and ecchymosis 7
• Ischemic priapism: Completely rigid corpora cavernosa requiring immediate intracavernous treatment 7
• Urethral injury: Evaluate if blood is present at meatus, gross hematuria, or inability to void 7

Diagnostic Approach

Confirm urethritis is present by documenting:

• Mucopurulent or purulent discharge 1
• Gram stain showing ≥5 WBCs per oil immersion field on urethral swab 1
• Positive leukocyte esterase test on first-void urine 1

Specific testing should include:

• Gram stain to identify intracellular Gram-negative diplococci (gonorrhea) 1
• Nucleic acid amplification tests for N. gonorrhoeae and C. trachomatis on first-void urine 1
• Culture or wet mount for T. vaginalis if initial treatment fails 1

Critical Pitfalls to Avoid

• Never delay surgical consultation if penile abscess is suspected, as rapid progression can occur within 24 hours 4
• Do not assume all penile discharge originates from the urethra—examine for median raphe canals or parameatal ducts as alternative sources 5, 6
• Always rule out testicular torsion in patients with scrotal/testicular swelling, especially in younger patients 7
• Do not confuse traumatic lymphedema with infectious causes—the former lacks systemic signs and has a clear history of vigorous sexual activity 8
• Ensure partner notification and treatment for all sexually transmitted causes to prevent reinfection 1