LAUSR

Background Advanced imaging modalities such as ultrasound (US) and dual-energy CT (DECT) can help diagnose crystalline arthritis. DECT is highly sensitive and specific in gout and has not been well studied in pseudogout. Objectives To compare the sensitivity of DECT, US, and x-ray (XR) in pseudogout. Methods We prospectively enrolled patients with crystal-proven pseudogout at a tertiary care center, 3/2018-11/2018. We searched the electronic medical record for synovial fluid crystal lab orders and reviewed the record to identify candidates. Eligible patients were 18 years old with acute monoarthritis, joint aspiration, and synovial fluid calcium pyrophosphate (CPP) crystals on polarized microscopy. Patients with both monosodium urate and CPP crystals were excluded. Subjects provided informed consent and underwent DECT, US, and XR of the aspirated joint and standardized joint (right wrist). All images were interpreted by a musculoskeletal radiologist and a rheumatologist trained in US; consensus was reached on each image. DECT images were post-processed using Siemens Syngo.via software, applying color-coded overlay indicating volume and location of CPP deposits. We considered two volume thresholds (cm3) for a positive DECT scan. Imaging abnormalities defining a positive scan were: color-coded changes consistent with CPP (DECT); hyperechoic deposits in hyaline-, fibro-cartilage, or tendon (US); and chondrocalcinosis in hyaline- or fibro-cartilage (XR). We calculated sensitivity and 95% confidence interval (CI) of positive scans in the aspirated joint and prevalence (95% CI) in the standardized joint. Results Ten of 27 eligible patients enrolled. Mean (SD) age was 73 (9.7) years; 40% were female. Eight knees and two wrists were aspirated a mean (SD) of 17 (9) days before enrollment. Six subjects received intra-articular steroids before enrollment. Imaging results are shown in Table 1. In the aspirated joint, sensitivity (95% CI) was 90% (71-100%) for DECT volume >0.40 cm3, and 100% (100-100%) for DECT volume >0.01 cm3; 100% (100-100%) for US; and 70% (42-98%) for XR. In the standardized joint, DECT was positive in 20% (0-45%) for volume >0.40 cm3, and 90% (71-100%) for volume >0.01 cm3. XR chondrocalcinosis was present in 30% (2-58%) and US was positive in 80% (55-100%) of wrists. Conclusion DECT and US had high sensitivity for pseudogout using synovial fluid CPP crystals as the gold standard. Larger studies testing DECT sensitivity and specificity in pseudogout vs. other arthritis and establishing a volume threshold are needed. References noneTable 1 Presence and location of imaging abnormalities in 10 pseudogout subjects Aspirated joint Standardized joint (right wrist) Subject DECT color–coded changes (cm3) US hyperechoic deposits XR chondro–calcinosis DECT color–coded changes (cm3) US hyperechoic deposits XR chondro–calcinosis 1 PF, PSFC, M, TF, (0.48) M M IC, IP1, MCP3, RC, TFCC (0.07) TFCC TFCC 2 ICN, M (0.73) FC, M M CMC1 (0.08) TFCC none 3 ICN, M, PF, TF (2.85) FC ICN, M, PF CMC1, CMC3, IC, IP1, MCP2, RC, TFCC (0.51) TFCC not done 4 ICN, M, PF, PSFC, Pop, Q (1.05) FC M IC (0.10) none none 5 M, PSFC, Q (0.50) FC M, PF IC, TFCC (0.04) TFCC none 6 M, PF (0.67) FC none CMC1, IC (0.03) TFCC CMC1 7 M, PF, PSFC (1.33) FC, M M, PF none (0.01) TFCC none 8* IC (0.02) IC, TFCC none IC (0.02) IC, TFCC none 9 M (0.45) M none IC (0.05) TFCC none 10 CMC1, IC, MCP1–5, TFCC (0.82) TFCC IC, MCP1–2, RC, TFCC CMC1, IC, MCP1–5, TFCC (0.84) none IC, MCP1–4, TFCC *Right wrist was the aspirated and standardized joint. CMC: carpometacarpal. FC: femoral cartilage. ICN: intercondylar notch. IP: interphalangeal. M: meniscus. MCP: metacarpophalangeal. PF: patellofemoral. Pop: popliteus tendon insertion. PSFC: posterior superior femoral condyle. Q: quadriceps tendon. RC: radiocarpal. TF: tibiofibular. TFCC: triangular fibrocartilage complex. Disclosure of Interests Sara Tedeschi: None declared, Daniel Solomon Grant/research support from: Abbvie, Amgen, Genentech, Janssen, and Pfizer, Kathleen Vanni: None declared, Neal Suh Grant/research support from: Pfizer, Stacy Smith: None declared