Differential Diagnosis for a 46-year-old with a Swollen Testicle

Single Most Likely Diagnosis

• Epididymitis: Although the patient's STI testing is negative, epididymitis can also be caused by non-sexually transmitted bacteria, especially in older men. The elevated white blood cell count suggests an infectious or inflammatory process, which aligns with epididymitis.

Other Likely Diagnoses

• Orchitis: Similar to epididymitis, orchitis (inflammation of the testicle) could present with swelling and an elevated white blood cell count. It can be caused by viral or bacterial infections.
• Testicular Torsion (partial or intermittent): Although typically painful, some cases of testicular torsion can present with minimal or no pain, especially if the torsion is partial or intermittent. The absence of pain does not rule out this condition entirely.
• Hydrocele: A hydrocele is an accumulation of fluid in the tunica vaginalis, a potential space around the testicle. It can cause swelling of the testicle and is usually painless.

Do Not Miss Diagnoses

• Testicular Cancer: While less common, testicular cancer can present with a painless swelling of the testicle. Given the potential severity of this diagnosis, it is crucial not to miss it, even though it might not be as likely as other conditions.
• Acute Appendicitis (with a retrocecal appendix): Although rare, an inflamed appendix located behind the cecum can sometimes cause testicular swelling due to the proximity of the appendix to the testicular vessels. This would be an unusual presentation but is a condition that could have serious consequences if not addressed.

Rare Diagnoses

• Spermatocele: A spermatocele is a cystic structure that arises from the head of the epididymis and contains sperm. It can cause swelling but is usually painless and discovered incidentally.
• Varicocele: A varicocele is an enlargement of the veins within the scrotum, similar to varicose veins. It can cause swelling and is typically painless, but the swelling is usually more pronounced on the left side due to anatomical differences in venous drainage.

Given the patient's presentation, a thorough physical examination, ultrasound of the scrotum, and possibly further laboratory tests (to rule out conditions like testicular cancer) would be essential for making an accurate diagnosis and guiding treatment.