Lower cost ultrasound beats gold standard in assessment of psoriatic arthritis

Standard musculoskeletal ultrasound is better than gold standard radiography at detecting overall joint pathology in the hands and feet of patients with psoriatic arthritis. MR imaging showed marginally better sensitivity at detecting joint effusions and synovitis, while radiography detected more erosions in the joints. But the low cost and comparable performance of ultrasound make it a viable tool for assessment of the small joints of patients with psoriatic arthritis.

Dr. Stefan M. Weiner of the department of rheumatology, immunology, and nephrology at the Teaching Hospital of the University of Mainz in Trier, Germany, and colleagues from other hospitals in Germany and Switzerland published their study in Clinical Rheumatology, which made it available online Feb. 8.

The researchers examined the small joints in the hands and feet of 13 consecutive psoriatic arthritis patients with B-mode ultrasound, using a 9 to 13-MHz transducer. At the same time, they performed MRI, bone scinitigraphy, radiography, and clinical exams for comparison. Radiography exams were done on 190 joints, 182 were examined with MRI, and 109 were examined with scinitigraphy.

Ultrasound, MRI, and scintigraphy were better at detecting overall joint pathology in painful, swollen joints. Ultrasound had a sensitivity of 71%, MRI had a sensitivity of 72%, and scintigraphy had a sensitivity of 82% versus 32% for radiography.

Radiography was considered the gold standard test for detection of erosions and osteoproliferations, and ultrasound compared favorably with it at detecting erosions and was better than MRI, although there was low agreement between methods. Radiography was better than ultrasound at visualizing osteoproliferations.

MRI was used as the gold standard for detecting joint effusion and synovitis, and it did better than ultrasound. Agreement between the two methods was good, however, in carpal joints, carpometacarpal joint I, and metacarpophalangeal/metatarsophalangeal joints I, II, and V. It was less so in metacarpophalangeal/metatarsophalangeal joints III and IV and proximal and distal interphalangeal joints.

Ultrasound specificity depended on the joint pathology, but compared with MRI, radiography, and scintigraphy, it ranged between 84% and 94%.

The researchers concluded that while ultrasound may not match up completely with MRI, the acceptable specificity and lower cost of ultrasound make it a useful diagnostic imaging method, especially when used in conjunction with radiography.