The correct answer is E. A monoarticular arthritis should raise the question of a septic versus a crystalline arthritis. Septic arthritis and crystalline arthritis can be notoriously similar in their clinical presentations, so clearly establishing the diagnosis, particularly in a patient with no known history of crystalline disease, is of great advantage before initiating definitive therapy. Crystal-induced and septic-induced joint can coexist in the same joint. An arthrocentesis is the most appropriate choice and allows examination of fluid for WBCs, crystals, and bacteria.
Colchicine (choice A) , NSAIDs (choice B) , and antibiotics (choice C) are all inappropriate before the arthrocentesis. If diagnosis of a septic joint is missed, the joint can be destroyed from the bacteria. A radiograph (choice D) would not yield a definitive diagnosis in this situation.
PEARL: Any patient who has a hot, swollen, inflamed, and motion-restricted joint should have aspiration performed to help determine the diagnosis. If this joint is a prosthetic joint, this aspiration should be performed in the operating room to perform this aspiration under aseptic conditions.
American College of Rheumatology guidelines for a patient with monoarticular arthritis after completion of a thorough history and physical examination:
- Patients who have a history of significant trauma or focal bone pain should have plain radiographs of the affected joint to rule out fracture, tumor, or metabolic bone disease.
- In the absence of a history of trauma or following a radiograph which excludes fracture or dislocation, an effusion or other signs of inflammation are markers of infection until proven otherwise. Joint aspiration is therefore the next diagnostic step.
- A bloody effusion should lead to consideration of a coagulopathy, pseudogout, tumor, trauma, or a Charcot joint; subsequent evaluation includes a PT, PTT, platelet count, and bleeding time.
- Bone marrow elements present in the synovial fluid are suggestive of an intra-articular fracture.
- A noninflammatory synovial fluid (e.g., <2,000 WBCs or <75% neutrophils) should lead to consideration of osteoarthritis, soft-tissue injury, or viral infection.
- Inflammatory joint fluid with crystals establishes the diagnosis of gout or pseudogout.
- A positive synovial fluid culture establishes the diagnosis of infectious arthritis.
- A sterile inflammatory joint fluid raises the suspicion of systemic rheumatic disorders; such patients should have further evaluation that may include a CBC, ESR, RF, anti-CCP, liver function tests, HLA-B27, ANA, or Lyme serologies.
