A 30-year-old man presents with joint pain and urethral edema. What is the most likely diagnosis?

The presentation of joint pain and urethral edema in a 30-year-old man strongly suggests reactive arthritis. Reactive arthritis is a type of inflammatory arthritis that occurs in response to an infection elsewhere in the body, often following an infection of the urogenital or gastrointestinal tract. In this case, the urethral edema indicates a potential urogenital infection, commonly due to sexually transmitted infections such as Chlamydia or Gonorrhea.

The joint symptoms, which can be asymmetrical and often affect the lower limbs, coexist with the urethral symptoms, fitting the clinical picture of reactive arthritis. Patients typically present with sudden onset of joint pain, often in a pattern involving one or a few joints, rather than multiple joints simultaneously.

In contrast, rheumatoid arthritis usually presents with symmetric polyarthritis, affecting small joints like the hands and is not typically associated with urethral symptoms. Septic arthritis would present more acutely with significant inflammation, possible fever, and is usually accompanied by a single swollen joint, making it a different clinical picture. Systemic lupus erythematosus could cause joint pain but is unlikely to specifically present with urethral edema as part of its symptomatology without other systemic findings.

Thus, the combination