A Hot Knee on Immunosuppression: Flare, Gout, or Infection?
Ms. D, 58, has seropositive rheumatoid arthritis treated with methotrexate 20 mg weekly, prednisone 10 mg daily, and adalimumab. She presents with a 30-hour history of a hot, swollen right knee that began without injury. Temperature is 38.2 C, HR 104, BP 106/64, WBC 13,200, and CRP 180. She had an intra-articular corticosteroid injection into that knee 4 weeks ago. She cannot bear weight. The resident documents 'RA flare - continue current therapy, increase prednisone, discharge with NSAIDs.'
1. What is the priority diagnosis, and why is RA flare being assumed a mistake?
Read the worked answer
Priority diagnosis: septic arthritis until proven otherwise
Why flare cannot be assumed
- Systemic signs: fever, tachycardia, and a borderline blood pressure suggest infection or sepsis, not an isolated flare.
- Markers: WBC and CRP are elevated, but these are nonspecific in inflammatory disease, so they cannot settle the question.
- Immunosuppression: methotrexate, prednisone, and a TNF inhibitor blunt the fever and inflammatory response, so infection may look milder than expected.
- Recent intra-articular injection is a recognized route for joint infection.
- Acute monoarthritis in one joint with inability to bear weight is septic arthritis until aspiration proves otherwise.
Nursing action
- Escalate the plan to the resident and attending with a structured rationale.
- Ask for urgent arthrocentesis before antibiotics if the patient is hemodynamically stable, so that cultures are not sterilized.
- Obtain blood cultures and monitor for sepsis; do not delay antibiotics in an unstable patient.
- Continue to reassess vital signs, mentation, and perfusion.
2. Synovial fluid shows 60,000 WBCs with 92% neutrophils, negative Gram stain, and calcium pyrophosphate crystals. How do you interpret this and what changes?
Read the worked answer
Interpretation
- A WBC count above roughly 50,000 with a neutrophilic predominance is highly suspicious for septic arthritis, even with a negative Gram stain. Gram stain is positive in only a portion of cases.
- Crystals do not exclude infection. Crystal disease and septic arthritis can coexist, and the crystals may be an incidental finding in an older adult with joint disease.
- The final answer depends on culture, which takes time.
What changes
- Nothing about the urgency: the patient needs empirical IV antibiotics after cultures, joint drainage as ordered, and admission.
- The team should not discharge her with NSAIDs and a higher prednisone dose based on the crystals.
- Rheumatology should be involved, and her immunosuppressants should be reviewed for holding.
- Monitor renal function before NSAIDs are used at all; NSAIDs are generally avoided in this setting.
3. What safety considerations surround her immunosuppressants, steroid coverage, and discharge planning?
Read the worked answer
Immunosuppressants
- Methotrexate and adalimumab are typically held during serious infection, but the decision belongs to the treating team and rheumatology. Nursing should confirm and document the plan.
- Because she is on chronic prednisone, she is at risk for adrenal insufficiency; ask whether stress-dose steroids are ordered if she becomes hypotensive or septic.
Monitoring and safety
- Watch for clinical deterioration: this patient may not mount a high fever.
- Assess glucose, since steroids and infection both raise it.
- Review analgesia: avoid nephrotoxic combinations and sedatives that obscure mental status.
- Fall precautions, since she cannot bear weight.
Discharge planning
- Discharge should not occur until infection is addressed; plan for IV antibiotic duration, line care, and who will administer it.
- Teach her the signs of recurrence and of line infection, and give clear return precautions.
- Confirm understanding with teach-back and document it, plus any need for an interpreter or home support.