What is the appropriate workup for calcium pyrophosphate deposition disease (CPPD) arthropathy identified on a hip radiograph?

Workup for CPPD Arthropathy Identified on Hip X-ray

When CPPD arthropathy is noted on hip radiograph, perform arthrocentesis with synovial fluid analysis to confirm crystal deposition, screen for metabolic disorders (especially in patients under 60), and review medications that may precipitate CPPD. 1

Confirm the Diagnosis with Synovial Fluid Analysis

• Arthrocentesis is the definitive diagnostic test and should be performed whenever possible to secure the diagnosis by identifying calcium pyrophosphate crystals under polarized light microscopy. 1
• Use ultrasound guidance for hip aspiration when anatomical landmarks make the procedure challenging, as this improves success rates and avoids ionizing radiation. 1
• Do not rely solely on imaging findings, as chondrocalcinosis on radiographs is common in elderly patients and may be asymptomatic—other conditions can mimic CPPD clinically and radiographically. 1

Complete Metabolic Screening (Mandatory for Age <60)

Screen for underlying metabolic conditions that cause secondary CPPD, particularly in patients presenting before age 60: 1

• Serum magnesium to detect hypomagnesemia 1
• Iron studies (serum iron, ferritin, transferrin saturation) to screen for hemochromatosis, which requires early identification in younger patients 1
• Serum calcium and parathyroid hormone (PTH) to evaluate for hyperparathyroidism 2

The 2023 EULAR guidelines emphasize mandatory screening for these conditions in early-onset disease, as they are treatable causes of CPPD. 1

Review Current Medications

• Identify medications that may precipitate CPPD, particularly loop diuretics like furosemide that cause magnesium depletion. 1
• Consider discontinuation or substitution of offending agents when clinically appropriate. 1

Assess Clinical Phenotype

• Determine whether the patient has acute pseudogout attacks requiring rapid symptom relief versus chronic CPPD arthropathy requiring long-term symptom control, as management differs substantially between these presentations. 1
• Document the pattern and distribution of joint involvement, as CPPD commonly affects knees, wrists, hips, and shoulders. 3

Additional Imaging Considerations

• Serial imaging is NOT recommended for monitoring CPPD unless there is unexpected clinical deterioration—unlike gout, there is no evidence supporting routine follow-up imaging. 1
• If axial involvement (such as crowned dens syndrome) is suspected based on clinical symptoms, consider CT imaging of the affected area. 4, 5
• Ultrasound can detect CPP crystal deposits at the hip with 90% sensitivity and 85% specificity, particularly at the acetabular labrum fibrocartilage, and may be useful if radiographic findings are equivocal. 6

Key Diagnostic Pitfalls to Avoid

• Do not skip metabolic screening in younger patients (<60 years), as treatable conditions like hemochromatosis and hyperparathyroidism require early identification. 1
• Do not assume the diagnosis without crystal confirmation when possible, even when radiographic chondrocalcinosis is present. 1
• Always perform synovial fluid Gram stain and culture if septic arthritis is in the differential diagnosis, as infection can coexist with crystal arthropathy. 7
• Recognize that conventional radiography detects only about 40% of clinically important CPPD, so negative radiographs do not exclude the diagnosis. 8