What are the diagnostic approaches and causes of orchitis?

Diagnosis and Causes of Orchitis

Diagnostic Approach

Orchitis diagnosis requires clinical evaluation combined with specific laboratory testing to identify the causative pathogen, with the diagnostic strategy differing based on patient age and risk factors. 1, 2

Clinical Presentation

• Men typically present with unilateral testicular pain, tenderness, and swelling 1
• Hydrocele and palpable epididymal swelling are usually present 1
• Fever and systemic symptoms may accompany bacterial orchitis 1
• Critical pitfall: Testicular torsion must be ruled out immediately, as it is a surgical emergency that occurs more frequently in adolescents and presents with sudden, severe pain 1

Essential Diagnostic Tests

For men <35 years (sexually transmitted pathogens suspected):

• Gram-stained smear of urethral exudate or intraurethral swab to diagnose urethritis (>5 polymorphonuclear leukocytes per oil immersion field) 1, 2
• Nucleic acid amplification tests (NAATs) are the most sensitive method for detecting Chlamydia trachomatis and Neisseria gonorrhoeae 1, 2
• NAATs can be performed on intraurethral swab or first-void urine 1
• First-void uncentrifuged urine examination for leukocytes if urethral Gram stain is negative 1
• Syphilis serology and HIV testing should be performed 1

For men >35 years (enteric organisms suspected):

• Urine culture and Gram-stained smear to identify gram-negative and gram-positive pathogens similar to those causing UTI 1
• First-void urine analysis for leukocytes and bacteria 1

Imaging:

• Ultrasound with color Doppler is recommended to confirm diagnosis and rule out testicular torsion, abscess, or tumor 2, 3
• Emergency imaging for torsion is indicated when pain onset is sudden, pain is severe, or initial tests don't support urethritis/UTI 1

Special Diagnostic Considerations

Viral orchitis:

• IgM serology for mumps antibodies or acute and convalescent IgG serology establishes diagnosis 1, 2
• Other viral causes include Coxsackie virus, rubella virus, Epstein-Barr virus, and varicella zoster virus 1, 2

Fungal and mycobacterial orchitis:

• Surgically obtained tissue may be required for culture 1
• Critical: Clinician must communicate with laboratory to ensure proper medium selection and processing for fungal and mycobacterial cultures 1
• Systemic fungal diseases (blastomycosis, histoplasmosis, coccidioidomycosis) and Mycobacterium tuberculosis can involve the testis 1, 2
• These are more likely in immunosuppressed patients 1, 2

Causes of Orchitis

Age-Based Etiology

Men <35 years:

• Chlamydia trachomatis is the most common sexually transmitted pathogen 1, 4
• Neisseria gonorrhoeae is the second most common STI cause 1
• In one ED study, 13.8% of men <35 with orchitis tested positive for STIs, with chlamydia (12.3%) more common than gonorrhea (3.1%) 4
• Sexually transmitted enteric organisms (E. coli) occur in men who are insertive partners during anal intercourse 1

Men >35 years:

• Gram-negative enteric organisms (primarily E. coli) are most common 1, 4
• E. coli was the most common bacteria in urine cultures of men with orchitis, followed by Streptococcus, Klebsiella, Pseudomonas, and Serratia 4
• Associated with urinary tract infections, recent urinary tract instrumentation/surgery, or anatomical urinary tract abnormalities 1

Viral Causes

• Mumps virus is the most frequent viral cause of orchitis 1
• Other viral etiologies include Coxsackie virus, rubella virus, Epstein-Barr virus, and varicella zoster virus 1, 2

Less Common Causes

• Brucellosis should be considered in endemic areas, particularly with history of raw milk ingestion 5
• Systemic fungal infections (blastomycosis, histoplasmosis, coccidioidomycosis) 1, 2
• Mycobacterium tuberculosis 1, 2
• Fungi and mycobacteria are more likely in immunosuppressed/HIV-infected patients 1, 2

Mechanism of Infection

• Bacterial orchitis most frequently occurs by extension from contiguous epididymal infection 1
• Retrograde propagation through the vas deferens is the main route for epididymal infection 6
• Viral orchitis occurs via hematogenous dissemination 6

Important Clinical Pearls

• Only 50.1% of men diagnosed with orchitis in the ED receive appropriate STI testing, representing a significant diagnostic gap 4
• Persistent swelling after antimicrobial therapy completion requires comprehensive evaluation for tumor, abscess, infarction, testicular cancer, tuberculosis, or fungal infection 1, 2
• Leucocytosis can occur in brucellar orchitis and cannot reliably differentiate it from nonspecific bacterial causes 5