Background Both RA and PsA are associated with hand involvement including synovitis and tenosynovitis. Differentiation between RA and PsA can sometimes be impossible using existing serological, genetic and imaging biomarkers.
At the micro anatomical level PsA is strongly linked to disease localisation to entheses and other sites of high mechanical stressing. Recently high resolution MRI has shown prominent abnormalities at the mini-entheses of the flexor tendon pulleys may be common (1).
Objectives This study tested the hypothesis that that mini-entheses disease of the hand including the A1,3, and 5 pulleys and flexor tendon insertion could be used to differentiate between RA and PsA.
Methods 46 cases of seropositive RA and 37 PsA patients were consecutively recruted. Cases were matched for disease duration, age and BMI with the majority being under therapy with conventional DMARDs (table1). Patients underwent completely rheumatological examination (AM, MC) and CRP and ESR determination. US examination was done with ESAOTE MyLabClass equiped with 18–6 linear probe. The 2nd to 4th dominant finger were scanned both on the dorsal and palmar surface. The sonograraphers (IT, PM) were blinded to the clinical details. The following changes were recorded as present (1) or absent (0): tendon flexor tenosynovitis, flexor pseudotensynovitis (peritendinous oedema), bone formation and the DIP flexor tendon insertion enthesophyte or calcifcations. A1, 3 and 5 pulley tendon thickness was measured at the level of maximal thickness in longitudinal or transverse way. The ecogenicity of the pulley was recorded as normal (if anecogen) or abnormal (no complete anecogenicity).
Results Flexor tenosynovitis was evident in 25/108 digits in PsA versus 8/135 in RA (p<0.001). Peritendinous oedema was evident in 23/108 PsA digit compared to only 8/135 RA digit (p<0.001) despite the fact that the magnitude of tenosynovitis was the same in RA and PsA. The A1, A3 and A5 pulleys were not significantly thicker in PsA compared to RA. Flexor tendon enthesopathy as determined by intra tendinous new bone was evident in 78/108 PsA cases, 21/135 RA and 2/30 health control (p<0.001 for both comparisons.
Conclusions This study suggests that PsA cases have a much higher burden of abnormalities in the min-entheses of the hand flexor tendons. With the improving resolution and capabilities of MKUS these findings may be relevant for defining the phenotype of joint swelling as RA (synovial centric) or SpA (entheseal like).
Tan AL. High-resolution MRI assessment of dactylitis in psoriatic arthritis shows flexor tendon pulley and sheath-related enthesitis.Ann Rheum Dis. 2015 Jan;74(1):185–9.
Disclosure of Interest None declared