Differential Diagnosis for the 45-year-old Male Patient

The patient presents with a history of gout in the right elbow, recent completion of antibiotics, and new onset of pain and swelling in the right knee, ankle, and shoulder, along with difficulty walking. Considering these symptoms, the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis

  • Septic Arthritis or Polyarticular Septic Arthritis: Given the patient's recent history of gout and completion of antibiotics, along with the new onset of joint pain and swelling in multiple joints, septic arthritis is a strong consideration. The transition from a single joint involvement to multiple joints could indicate a spread of infection, especially if the initial antibiotic treatment was not fully effective or if the patient has a predisposing condition for infections.

• Other Likely Diagnoses

  • Polyarticular Gout: Although the patient was diagnosed with gout in one elbow, gout can become polyarticular over time, especially if not well-managed. The new symptoms could represent a flare of gout affecting multiple joints.
  • Rheumatoid Arthritis (RA): This autoimmune disorder can cause symmetric polyarthritis, which might be considered given the patient's symptoms of multiple joint involvement. However, the acute onset and the patient's history might make this less likely compared to other options.
  • Pseudogout (Calcium Pyrophosphate Deposition Disease, CPPD): Similar to gout, pseudogout can cause acute arthritis and can be polyarticular. It might be considered, especially if the patient has risk factors for CPPD.

• Do Not Miss Diagnoses

  • Endocarditis with Septic Emboli: Although less common, if the patient has a history of heart disease or other risk factors for endocarditis, this condition could lead to septic emboli causing multiple joint infections. It's critical to consider this diagnosis due to its high mortality rate if left untreated.
  • Lyme Disease: If the patient lives in an area endemic for Lyme disease and has been exposed to ticks, Lyme arthritis could be a consideration, especially if the patient presents with a distinctive "bull's-eye" rash or other systemic symptoms.
  • Gonococcal Arthritis: This condition, caused by Neisseria gonorrhoeae, can present with polyarticular symptoms and is a critical diagnosis not to miss due to its implications for treatment and public health.

• Rare Diagnoses

  • Seronegative Spondyloarthropathies (e.g., Psoriatic Arthritis, Reactive Arthritis): These conditions can cause polyarthritis but are less likely given the patient's presentation and history. They might be considered if other diagnoses are ruled out and the patient has specific risk factors or associated symptoms (e.g., psoriasis, recent gastrointestinal or genitourinary infection).
  • Hemochromatosis: This genetic disorder can lead to arthropathy similar to osteoarthritis but can also cause acute presentations. It's rare but could be considered if the patient has a family history or other suggestive symptoms.
  • Sarcoidosis: This condition can cause polyarthritis among its many manifestations. It would be a rare consideration but might be entertained if the patient has other systemic symptoms suggestive of sarcoidosis (e.g., lung findings, skin lesions).