Diagnostic accuracy of ultrasound, conventional radiography and synovial fluid analysis in the diagnosis of calcium pyrophosphate dihydrate crystal deposition disease.

OBJECTIVES: To assess the diagnostic performance of ultrasound (US), x-rays, and microscopic analysis of synovial fluid (SF) for calcium pyrophosphate dihydrate crystal deposition disease (CPPD) using histology as a reference standard.
METHODS: We enrolled consecutive patients with osteoarthritis waiting to undergo knee replacement surgery. Each patient underwent US of the knee, focusing on menisci and the hyaline cartilage, the day before surgery. During surgery, SF, menisci and condyles were retrieved and examined microscopically. For the meniscus and cartilage microscopic analysis, 8 samples were collected from each specimen and knee radiographs, performed up to 3 months before surgery, were also assessed. A dichotomous score was given for the presence/absence of CPP for each method. Microscopic findings of the specimens were considered the reference standard. All the procedures followed were in accordance with the ethical standards of the local responsible committee.
RESULTS: 42 patients (14 males) were enrolled. All patients underwent US, 34 had eligible radiographs and 32 had SF analysis. 25 patients (59.5%) were positive for CPP at US, 15 (44.1%) at X-ray and 14 (43.7%) at SF. Sensitivity and specificity values were 96% and 87% for US, 75% and 93% for radiography and 77% and 100% for SF respectively. There were no statistically significant differences between the diagnostic performance across single tests.
CONCLUSIONS: US proved to be at least as accurate as SF analysis for the diagnosis of CPPD. US, which is feasible and harmless, could be considered the first exam of choice for CPPD diagnosis.