Pitfalls in diagnosing acute CPP crystal arthritis
• Septic arthritis can coexist (in up to 1% of cases) with an acute crystalline arthritis. Enzymes that degrade cartilage can be released into the joint (from the infecting bacteria or the PMNs). These enzymes are able to strip crystals from the structures in and around the joint, and an unwary clinician might miss a septic joint. This is why joint fluid should be sent for a Gram stain and culture on all arthrocenteses of acute arthritis.
• Pseudogout can present as pseudoseptic arthritis , an inflammatory arthritis that mimics septic arthritis; Gram stain and cultures are persistently negative . It is a diagnosis of exclusion.
• Although rare, it is possible for a patient to have simultaneous gout and pseudogout.
• Acute pseudogout in the wrist of an elderly person may cause a carpal tunnel syndrome. Similarly, CPP deposition can cause cubital tunnel syndrome.
• Up to 20% of patients with pseudogout may not have CC on radiography. The synovial fluid must be examined for crystals.
• Acute pseudogout is frequently precipitated by an urgent medical illness, such as myocardial infarction or a surgical procedure. Fluid shifts with fluctuations in serum calcium levels may play a role in such attacks. An elderly hospitalized patient who complains of new joint pain should be investigated for pseudogout.
• Other potential precipitators of pseudogout: Intraarticular hyaluronate (especially in products with high concentrations of phosphate such as Synvisc) has been linked to subsequent acute CPP crystal arthritis in case reports. Other possible associations include the use of loop diuretics, granulocyte–macrophage colony-stimulating factor and IV bisphosphonates.
