Msk Dermatology · Year 2 · from Msk Dermatology

Case 3: Rheumatoid Arthritis Flare with Septic Joint Concern

Patient Presentation

Demographics: 65-year-old man

Chief Complaint: "My left knee is extremely swollen and painful since yesterday."

History of Present Illness: The patient has a 10-year history of seropositive rheumatoid arthritis, currently on adalimumab and methotrexate with reasonable disease control. He presents with acute onset of severe left knee pain and swelling that began approximately 18 hours ago. The knee is more painful than his typical RA flares. He has had difficulty bearing weight and low-grade fever (38.2C) at home. He had a dental cleaning one week ago. He denies other recent infections, trauma, or tick bites.

Past Medical History:

• Rheumatoid arthritis
• Type 2 diabetes mellitus
• Coronary artery disease with stent 3 years ago

Medications:

• Adalimumab 40 mg every 2 weeks (last dose 10 days ago)
• Methotrexate 20 mg weekly
• Folic acid 1 mg daily
• Metformin 1000 mg twice daily
• Aspirin 81 mg daily
• Atorvastatin 40 mg daily

Social History:

• Retired engineer
• Non-smoker

Physical Examination

• Vital Signs: BP 142/88 mmHg, HR 102 bpm, Temp 38.4C, RR 18
• General: Uncomfortable, diaphoretic
• Left Knee:
• Large tense effusion
• Significant warmth and erythema
• Exquisitely tender to palpation
• Unable to flex or extend due to pain
• Held in approximately 30 degrees of flexion
• Other Joints: Mild chronic synovitis at MCPs bilaterally, no acute inflammation

Workup and Results

Laboratory Studies:

Synovial Fluid Analysis:

Imaging:

• Left knee X-ray: Large effusion, chronic degenerative changes, no fracture

Diagnosis

Septic Arthritis of the Left Knee (presumed Staphylococcus aureus)

Risk Factors Present:

• Immunosuppression (TNF inhibitor, methotrexate)
• Diabetes mellitus
• Pre-existing joint disease (RA)
• Recent dental procedure (potential source of bacteremia)

Treatment Plan

Emergent Management:

1. Orthopedic surgery consultation for urgent arthroscopic lavage/debridement
2. Hold adalimumab and methotrexate - do not resume until infection cleared
3. IV antibiotics:

• Empiric: Vancomycin 1.5g IV q12h (cover MRSA given immunosuppression and healthcare exposure)
• Narrow based on culture results

1. Serial knee aspirations if surgery delayed; may need repeated drainage

Supportive Care:

1. IV fluids
2. Pain management (avoid NSAIDs given kidney considerations)
3. Diabetes management - insulin sliding scale while acutely ill

Duration:

• Minimum 4 weeks IV antibiotics for native joint septic arthritis
• May transition to oral if organism susceptible and good response

Follow-up Considerations:

1. Echocardiogram to rule out endocarditis (dental source, bacteremia)
2. Repeat synovial fluid analysis to confirm sterilization
3. Physical therapy once infection resolved
4. Discussion of RA therapy restart timing (typically 2-4 weeks after antibiotics completed)

Teaching Points

1. Septic arthritis in RA: Patients on immunosuppression are at increased risk; must maintain high clinical suspicion even if presentation overlaps with RA flare
2. TNF inhibitors and infection: Increase risk of serious infections, particularly bacterial and mycobacterial; must be held during active infection
3. Synovial WBC >50,000: Strongly suggests septic arthritis; crystals should also be excluded as they can coexist
4. Gram-positive cocci in clusters: Likely Staphylococcus aureus, the most common cause of septic arthritis
5. Urgent drainage: Essential for joint preservation; delays of even 24-48 hours worsen outcomes and risk of permanent joint damage
6. Pre-existing joint disease: Damaged joints (RA, OA) are more susceptible to bacterial seeding during bacteremia; dental procedures, urinary tract infections, and skin infections are common sources

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