What is the difference between orchitis and epididymo-orchitis?

Differences Between Orchitis and Epididymo-Orchitis

Orchitis is inflammation limited to the testis only, while epididymo-orchitis involves inflammation of both the epididymis and testis, with infection typically spreading from the epididymis to the testis. 1, 2

Anatomical and Pathophysiological Differences

• Orchitis:

  • Inflammation confined to the testicular tissue
  • Can occur as an isolated condition (less common)
  • Often caused by hematogenous (bloodborne) spread of infections, particularly viral pathogens
  • Classic example is mumps orchitis, diagnosed by IgM serology for mumps antibodies 1

• Epididymo-orchitis:

  • Involves both the epididymis and testis
  • More common than isolated orchitis
  • Typically begins as epididymitis with retrograde spread to the testis
  • Usually caused by bacterial pathogens that ascend through the vas deferens 2

Etiological Differences

Orchitis

• Primary viral causes:
  • Mumps virus (most common viral cause)
  • Other viral causes: Coxsackie virus, rubella virus, Epstein-Barr virus, varicella zoster virus 1
• Less commonly bacterial (usually as extension from epididymitis)
• Rare causes: Mycobacterium tuberculosis, systemic fungal infections (blastomycosis, histoplasmosis, coccidioidomycosis) 1

Epididymo-orchitis

• Age-dependent bacterial causes:
  • Men <35 years: Primarily sexually transmitted infections (Chlamydia trachomatis, Neisseria gonorrhoeae) 1
  • Men >35 years: Primarily enteric organisms (E. coli and other uropathogenic bacteria) 1, 3
• Associated conditions:
  • Urinary tract infections
  • Urinary tract abnormalities or obstruction
  • Prostate conditions (BPH, prostatitis)
  • Recent urinary tract instrumentation 1, 4

Clinical Presentation Differences

• Orchitis:

  • May have systemic viral symptoms (fever, malaise, myalgia)
  • Testicular pain and swelling without epididymal involvement
  • In mumps orchitis: parotid gland swelling may precede testicular symptoms by 3-7 days

• Epididymo-orchitis:

  • Typically unilateral testicular pain and swelling
  • Swelling classically begins at the lower pole of the epididymis and progresses upward 4
  • May have associated urethral discharge (especially in STI cases)
  • Often accompanied by urethritis, which may be asymptomatic 1
  • Positive Prehn sign (pain relief with testicular elevation) 5

Diagnostic Approach

Imaging

• Ultrasound with Doppler is the primary imaging modality for both conditions 1, 5

• Orchitis findings:

  • Enlarged, hypoechoic testis
  • Increased blood flow within testicular tissue

• Epididymo-orchitis findings:

  • Enlarged, hypoechoic epididymis
  • Testicular involvement with increased blood flow
  • Scrotal wall thickening and hydrocele are common 1

Laboratory Testing

• Orchitis:

  • Viral serology (IgM antibodies or acute/convalescent IgG) for suspected viral causes
  • Urine studies may be normal

• Epididymo-orchitis:

  • Urethral Gram stain and culture (for N. gonorrhoeae)
  • Nucleic acid amplification tests for C. trachomatis and N. gonorrhoeae
  • Urinalysis and urine culture (especially in men >35 years) 1
  • Complete blood count may show leukocytosis

Treatment Differences

Orchitis

• Viral orchitis:

  • Primarily supportive care (rest, scrotal elevation, analgesics)
  • No specific antiviral therapy typically required

• Bacterial orchitis:

  • Antibiotics directed at the causative organism
  • Similar to epididymo-orchitis treatment if bacterial in origin

Epididymo-orchitis

• For men <35 years (likely STI):

  • Ceftriaxone 250 mg IM single dose PLUS
  • Doxycycline 100 mg orally twice daily for 10 days 1

• For men >35 years (likely enteric organisms):

  • Fluoroquinolones (e.g., ofloxacin 300 mg orally twice daily for 10 days) 1
  • Alternative antibiotics due to increasing fluoroquinolone resistance 3
  • Consider hospitalization for severe cases requiring IV antibiotics 1, 4

Complications

• Orchitis:

  • Testicular atrophy
  • Infertility (especially with bilateral mumps orchitis)

• Epididymo-orchitis:

  • Abscess formation
  • Testicular infarction (rare complication)
  • Chronic epididymal induration
  • Infertility
  • Chronic scrotal pain 5

Key Clinical Pearls

1. Isolated orchitis is less common than epididymo-orchitis
2. The most important differential diagnosis for both conditions is testicular torsion, which requires immediate surgical intervention
3. Age is an important factor in determining the likely etiology of epididymo-orchitis
4. Treatment should be initiated promptly to prevent complications and preserve fertility
5. Sexual partners should be evaluated and treated in cases of STI-related epididymo-orchitis 2