Background The sensitivity of ultrasound (US) signs of monosodium urate (MSU) deposition in symptomatic joints is only 60% with negative predictive value of 62% while multiple joins examination gives better sensitivity and better negative predictive value with less specificity though . The 12 sites' combination assessment has been proposed by Naredo and colleagues with 84, 6% sensitivity and 83, 3% specificity in late gout . Does it fit in the early gout?
Objectives To compare the frequencies and specificity of US dual contour sign (DC), tophus (T) in early versus late gout using multiple investigation of joints and tendons, most often affected by gout, in order to define the most suitable test for diagnosis of both early and late stage of the disease.
Methods Prospective single centre case - control study was performed. Crystal - proven gout compared according healthy controls. Systematic US assessment of 36 joints and 4 tendons (patellar and triceps) was done by rheumatologist, blinded to study group and clinical findings. The reliability of the US assessment was checked in a web – based exercise, evaluated by kappa coefficient. The early (symptoms ≤2 years) and rest gout was compared according frequency of DC and T in different anatomical sites using chi – square test. The specificity and sensitivity of T and DC in total investigated sites, in 10, 6 and 4 anatomical areas has been compared.
Results 50 patients with gout (16 early, 34 late gout) and 36 age matched healthy controls were investigated. In late gout US T sign was most often found in I MTF (79,4%), patellar tendon (39,7%), triceps tendon (38,2%), wrist (33,8%), II MCP, II MTF joint; DC sign - in I MTF (45,6%), knees (38,2%), ankles (35,2%), II MCP (27%), II MTP, III MTP. In early gout the most often T was in I MTF (65, 7%) and wrist (21,9%), DC – in I MTF (25%), ankles (22%), II MTF. There were no T found in II MCP and PIP joints, 0,6% in the rest MCP, less T found in m. triceps and patellar tendons than in late gout (p<0,001 and p<0,01 accordingly). There were less DC found in total MCP, II MCP, total PIP and knees joints in early than in late gout with p<0,001; <0,05; <0,01; <0,01 accordingly. The best balance between sensitivity (91%) and specificity (81%) has been noticed with 6 US abnormalities in 4 joints. The intrareader reliability was good (mean kappa 0,712).
Conclusions Our results suggest, that US signs of urate deposition in metacarpophalangeal and proximal interphalangeal joints, m. triceps and patellar tendons are very seldom found in gout with symptoms duration up to two years and might be the symptoms of late disease. Bilateral assessment of first metatarsophalangeal joint for tophus, dual contour sign and knee femoral cartilage for dual contour sign shows best balance between sensitivity and specificity diagnosing both early and late gout.
Zufferey P, Valcov R, Fabreguet I, Dumusc A, Omoumi P, So A. A prospective evaluation of ultrasound as a diagnostic tool in acute microcrystalline arthritis. Arthritis Res Ther. 2015;17(1):188. doi:10.1186/s13075-015-0701-7.
Naredo E, Uson J, Jiménez-Palop M, et al. Ultrasound-detected musculoskeletal urate crystal deposition: which joints and what findings should be assessed for diagnosing gout? Ann Rheum Dis. 2013:1–7. doi:10.1136/annrheumdis-2013-203487.
Disclosure of Interest None declared