Epididymo-Orchitis
Definition
Epididymo-orchitis: inflammation of the epididymis and testes
Isolated epididymitis can occur but is less common, as the inflammation often spreads to involve the testis as well.
Aetiology
Bacterial infections are most common, and the likely organisms vary by age: [Ref]
- <35 y/o (or those at risk for STIs): most commonly caused by STI organisms (Chlamydia trachomatis and Neisseria gonorrhoea)
- >35 y/o: most commonly caused by UTI organisms (e.g. Escherichia coli, Pseudomonas species)
Other uncommon infective causes:
- Mumps causes viral orchitis, typically 10–14 days after parotitis, and classically does not involve the epididymis
- Mycobacterium tuberculosis
- Fungus
Some rare, non-infectious causes:
- Amiodarone-induced epididymo-orchitis
- Autoimmune diseases (e.g. sarcoidosis, Bechets disease)
Clinical Features
Symptoms
Typically present as a subacute onset (over a few days) of unilateral scrotal pain and swelling
Other symptoms:
- Low-grade fever
- Features of UTI (e.g. dysuria, frequency, urgency)
- Features of urethritis (e.g. urethral discharge)
Signs
Typical examination findings:
- The epididymis and testis are usually enlarged, indurated, and exquisitely tender
- +ve Prehn’s sign (pain is relieved on elevation of the testis)
Testicular torsion is an important differential diagnosis. Key differentiating factors:
- Cremasteric reflex is preserved in epididymo-orchitis (but absent in testicular torsion)
- Testicular lie is normal in epididymo-orchitis (but retracted / high-riding testis in testicular torsion)
Complications
Complications are rare but can occur in cases with delayed diagnosis or inadequate treatment:
- Testicular abscess
- Testicular infarction
- Testicular atrophy
Investigation and Diagnosis
The following tests should be performed: [Ref]
- Urinalysis and mid-stream urine culture (to detect UTI organisms)
- NAAT of first void urine / urethral swab (to detect STI organisms)
In some exam questions, you may need to choose between urine culture and NAAT for the most appropriate initial investigation. The correct choice depends on the most likely causative organism:
- <35 y/o → STI more likely → NAAT more appropriate
- >35 y/o → UTI more likely → urine culture more appropriate
When the diagnosis is unclear / testicular torsion cannot be safely excluded → perform a scrotal ultrasound with Doppler [Ref]
- An enlarged, hyperemic epididymis with increased Doppler flow indicates epididymitis and excludes testicular torsion
- Note that Doppler flow is reduced in testicular torsion
If mump orchitis is suspected, perform PCR for mumps virus RNA or IgM serology for mumps antibodies
Management
Empirical antibiotic therapy should be offered, based on age and risk factors: [Ref]
| Patient category | 1st line antibiotics | Rationale |
|---|---|---|
| <35 y/o (or those at risk of UTI) |
|
To cover Chlamydia trachomatis and Neisseria gonorrhoea |
| >35 y/o |
|
To cover UTI organisms |
Treatment should be adjusted based on urine culture and antimicrobial susceptibility results.