Management of Acute Monoarticular Arthritis in a 72-Year-Old Man with Diabetes
Arthrocentesis (option B) is the most appropriate next step in management for this patient with suspected septic arthritis.
Clinical Presentation Analysis
This 72-year-old man presents with several concerning features that require immediate attention:
- Acute onset of swollen, painful, erythematous right knee
- Fever (38.0°C/100.4°F)
- Leukocytosis (14,500/μL)
- History of type 2 diabetes (risk factor for infection)
- History of gouty arthritis (potential confounding diagnosis)
The combination of monoarticular joint inflammation, fever, and leukocytosis strongly suggests septic arthritis, which is a medical emergency requiring prompt diagnosis and treatment.
Diagnostic Approach
Why Arthrocentesis is the Correct Choice:
According to the American College of Physicians guidelines, synovial fluid analysis is essential when clinical judgment indicates diagnostic testing is necessary in patients with possible acute gout 1. However, in this case, the primary concern is to rule out septic arthritis, which takes precedence over gout diagnosis.
The isolation of bacteria from synovial fluid is the gold standard (criterion standard) for diagnosing infectious arthritis 1, 2. Synovial fluid analysis provides critical information:
- Cell count and differential (septic arthritis typically >50,000 WBC/mm³)
- Crystal analysis (to evaluate for concurrent gout)
- Gram stain and culture (to identify causative organisms)
Why Other Options Are Incorrect:
Option A (Start colchicine): While the patient has a history of gout, treating empirically without ruling out infection could lead to devastating consequences if septic arthritis is present.
Option C (X-rays and indomethacin): Although indomethacin is indicated for acute gouty arthritis 3, treating with anti-inflammatory medication before establishing diagnosis could mask symptoms and delay appropriate treatment of a potential infection.
Option D (MRI of the knee): While MRI is useful for defining bone infection and deep soft tissue infections 1, it would delay the diagnosis of septic arthritis, which requires immediate intervention.
Management Algorithm
Perform arthrocentesis immediately
- Use sterile technique
- Consider ultrasound guidance for better accuracy 4
- Obtain adequate fluid for all necessary tests
Send synovial fluid for:
- Cell count with differential
- Crystal analysis (polarized light microscopy)
- Gram stain
- Culture and sensitivity
- Glucose and protein levels
Interpret synovial fluid results:
- WBC >50,000/mm³ suggests septic arthritis
- Presence of MSU crystals indicates gout (note: gout and infection can coexist)
- Positive Gram stain indicates bacterial infection
Initiate treatment based on arthrocentesis findings:
- If septic arthritis is suspected, start empiric antibiotics after cultures are obtained
- For gram-positive cocci: vancomycin
- For gram-negative cocci: ceftriaxone
- For gram-negative rods: ceftazidime
- If Gram stain is negative but clinical suspicion is high: vancomycin plus ceftazidime or an aminoglycoside 2
Important Clinical Considerations
Septic arthritis vs. Gout: Both can present with acute monoarticular arthritis, but septic arthritis is a medical emergency with significant morbidity and mortality if not treated promptly.
Diabetes as a risk factor: Patients with diabetes have increased risk for infections, including septic arthritis, and may have atypical presentations.
Coexistence of conditions: Crystal-induced arthropathy and septic arthritis can coexist, making arthrocentesis essential for accurate diagnosis 2.
Timing is critical: Delay in diagnosis and treatment of septic arthritis can lead to irreversible joint damage, systemic infection, and even death.
By performing arthrocentesis first, the clinician can make a definitive diagnosis and initiate appropriate treatment promptly, potentially preventing serious complications in this high-risk patient.