What is Prehn's sign and how does it differentiate epididymitis from testicular torsion?

Prehn's Sign: Definition and Clinical Utility

What is Prehn's Sign?

Prehn's sign is the relief of scrotal pain when the affected testicle is elevated above the symphysis pubis, traditionally taught to help differentiate epididymitis from testicular torsion. 1

• In epididymitis, elevating the scrotum typically relieves pain (positive Prehn's sign) because it reduces tension on the inflamed epididymis and improves venous drainage 1
• In testicular torsion, elevation does not relieve pain (negative Prehn's sign) because the ischemic injury from twisted spermatic cord persists regardless of position 1

Critical Limitation: Prehn's Sign is Unreliable

Prehn's sign should NOT be used to rule out testicular torsion because it lacks sufficient sensitivity and specificity. The most recent systematic review demonstrates that this clinical sign is dangerously unreliable:

• 33% to 100% of patients with confirmed testicular torsion had a positive Prehn's sign (pain relief with elevation), meaning the test gave false reassurance in up to one-third of torsion cases 2
• The negativity of Prehn's sign (no pain relief) ranged from 0% to 89.5% in patients with testicular torsion, showing extreme variability 2
• A 2018 multivariate analysis found that a positive Prehn's sign was actually predictive of testicular torsion, contradicting the traditional teaching 3
• In a Japanese surgical series, 37.5% of confirmed torsion cases demonstrated Prehn's sign, further invalidating its discriminatory value 4

Why Prehn's Sign Fails Clinically

The overlapping clinical presentations of epididymitis and testicular torsion make physical examination signs inherently unreliable:

• As epididymitis progresses, reactive hydrocele and scrotal edema develop, making it difficult to differentiate from torsion 1
• Testicular torsion can torse and detorse spontaneously, creating intermittent pain patterns that mimic inflammatory conditions 5
• Both conditions present with unilateral testicular pain, swelling, and tenderness—the physical findings overlap substantially 1, 3

The Correct Diagnostic Approach

When testicular torsion cannot be ruled out clinically, immediate surgical exploration is mandatory—do not rely on Prehn's sign. 3

Immediate Actions for Acute Scrotal Pain:

• Testicular torsion must be excluded first because testicular viability declines after 4–6 hours, and salvage rates drop from 88.9% (surgery <12 hours) to 13.3% (surgery >12 hours) 6, 4
• Order emergent Doppler ultrasound to assess testicular blood flow, though even this imaging modality has limitations in small pediatric testes 1
• Obtain urgent surgical consultation if the diagnosis is uncertain—exploration is both diagnostic and therapeutic 3

Clinical Features That Actually Help Differentiate:

For Epididymitis (more gradual presentation): 1, 6

• Gradual onset over hours to days
• Urethral discharge, dysuria, or urinary frequency in younger men (<35 years)
• Fever, elevated C-reactive protein, and leukocytosis
• Palpable epididymal swelling starting at the lower pole

For Testicular Torsion (surgical emergency): 1, 7

• Sudden onset of severe pain
• Nausea and vomiting common
• Absent cremasteric reflex (more reliable than Prehn's sign)
• High-riding testicle with abnormal lie

Common Pitfalls to Avoid

• Never delay surgical exploration based on a positive Prehn's sign—up to one-third of torsion cases may show pain relief with elevation 2
• Do not assume epididymitis in adolescents even with inflammatory signs—torsion has a bimodal distribution peaking in neonates and postpubertal boys 1
• Color Doppler ultrasound cannot reliably distinguish torsion from infection in all cases, particularly in early torsion with partial blood flow 3

Clinical Bottom Line

Prehn's sign is insufficiently sensitive to rule out testicular torsion; paradoxically, its negativity (no pain relief) may actually increase the likelihood of torsion diagnosis. 2 The American College of Radiology emphasizes that prompt recognition and surgical exploration within 6–8 hours is essential to prevent testicular loss, and clinical scoring systems have not been widely adopted despite validation 1. When acute scrotal pain presents, prioritize immediate imaging and surgical consultation over unreliable physical examination maneuvers 3.