Background Demonstration of mono-sodium urate crystals (MSU) in synovial fluid or tophus aspirate remains the definitive way to diagnose gout. In patients without synovial effusion or clinical tophi the sampling of relevant material to examine for MSU is challenging. Ultrasonography (US) detects changes in gout in the form of the double contour (DC) sign and synovial hyperecchoic foci (SHEF) which is considered to represent MSU deposits on the articular cartilage or in synovium respectively. The location of these US changes may guide the physician where to aspirate relevant synovial tissue to examine for MSU.
Objectives To evaluate the frequency of gout patients presenting without synovial effusions or clinical tophi and to evaluate the effectiveness of US guided dry-needle synovial tissue aspiration to demonstrate MSU crystals in these patients.
Methods Consecutive patients referred with clinical signs of gout were examined clinically for joint swelling and clinical tophi. MTP joints, knees, and symptomatic joints were examined with US. In cases with synovial effusions or clinically detectable tophi aspiration were done from these sites. In cases without synovial effusion or tophi, but with US signs of MSU deposits, dry needle aspiration with an intramuscular needle (21G/ 0.8 mm) were done from sites with SHEF or DC. The aspirated material was aired out from the needle onto a slide and examined in double phase polarization microscopy in the same manner as samples of synovial fluid or tophus aspirates.
Results Twenty consecutive patients diagnosed with crystal proven gout were included in this survey. Patient characteristics: 18 males/2 females, median age (range): 65(40-83) years, affected joints: feet: 7, knees: 4, wrists: 2, hands: 3, elbow: 1, oligo/polyarticular: 4. Seven patients had joint effusions and in all these cases MSU were detected in the synovial fluid. Five patients had clinical tophi and in all these cases MSU were demonstrated in aspirate from tophi. Eight patients had no synovial effusion or tophi, but by use of US guided dry needle synovial aspiration from joints with DC or SHEF, MSU were demonstrated.
In all 19 of 20 patients had ultrasonic signs of gout ( DC: 4, SHEF: 2, DC+SHEF: 14). One patient with short disease duration and synovial effusion with MSU in a knee had no US signs of gout.
During the study period was seen 1 patient highly suspected of gout with clinical arthritis in a wrist joint and with US signs of gout in the feet where MSU could not be detected in US guided dry needle synovial tissue aspirate – possibly due to sampling error, and this patient is not included in the survey. The US guided dry needle synovial tissue aspiration techniques was thus positive in 8/9 (89%) cases when used in patients with US signs of urate deposits.
Conclusions Eight out of 20 (40%) gout patients did not display synovial effusion or clinical tophi at the time of diagnosis. The diagnosis may thus have been missed or delayed due to lack of diagnostic demonstration of MSU crystals.
The US guided dry needle synovial aspiration technique proved useful in obtaining material for microscopy in patients without any signs of effusion or tophi and may thus increase the diagnostic sensitivity in gout.
Disclosure of Interest None Declared
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