Most Likely Organism in Scrotal Pain and Swelling
Neisseria gonorrhoeae is more likely than Mycoplasma genitalium to cause scrotal pain and swelling in sexually active men, particularly those under 35 years of age. 1, 2
Age-Dependent Pathogen Distribution
The causative organism depends critically on patient age:
Men Under 35 Years (Sexually Active)
- Neisseria gonorrhoeae and Chlamydia trachomatis are the predominant pathogens, accounting for the majority of sexually transmitted epididymitis cases 1, 3, 4
- These organisms cause epididymitis through retrograde ascent from urethritis, which is often asymptomatic 1
- In a recent ED study, among men <35 years diagnosed with epididymitis/orchitis who were tested, chlamydia (12.3%) was most common, followed by gonorrhea (3.1%) 5
Men Over 35 Years
- Enteric organisms (particularly E. coli and other Gram-negative bacteria) become the primary pathogens 1, 3
- These infections occur secondary to bladder outlet obstruction or urinary tract abnormalities 3, 6
Mycoplasma Genitalium's Limited Role
Mycoplasma genitalium is primarily a cause of urethritis, not epididymitis or scrotal pathology 1:
- Guidelines list M. genitalium as a urethritis pathogen requiring specific treatment (azithromycin 500 mg day 1, then 250 mg for 4 days) 1
- It does not appear in any guideline's differential diagnosis for acute epididymitis 1
- The 2024 European Association of Urology guidelines explicitly identify C. trachomatis, N. gonorrhoeae, and Enterobacterales as the predominant epididymitis pathogens—M. genitalium is notably absent 1
Clinical Approach to Diagnosis
Immediate evaluation should include 1:
- Gram-stained urethral smear (≥5 PMNs per oil immersion field indicates urethritis; intracellular Gram-negative diplococci suggest gonorrhea) 1
- Nucleic acid amplification testing for N. gonorrhoeae and C. trachomatis on urethral swab or first-void urine 1
- First-void urine examination for leukocytes, culture, and Gram stain 1
- Ultrasound with Doppler to exclude testicular torsion and identify complications 7
Critical Pitfall
The most dangerous error is missing testicular torsion, which requires emergency surgical intervention within 6-8 hours to preserve testicular viability 7:
- Torsion is more common in adolescents and presents with sudden, severe pain 1
- Torsion patients typically lack signs of inflammation or infection 1
- If diagnosis is uncertain, immediate surgical consultation is mandatory 1
Empiric Treatment Based on Likely Pathogen
For sexually active men <35 years, treat for both gonorrhea and chlamydia 1, 2:
- Ceftriaxone 250 mg IM single dose PLUS doxycycline 100 mg orally twice daily for 10 days 1, 2
- This dual therapy addresses the two most common sexually transmitted pathogens (N. gonorrhoeae and C. trachomatis) 2, 3
Reassess within 3 days if no improvement occurs—failure to respond requires reevaluation of both diagnosis and antimicrobial therapy 1, 2