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What is metacarpophalangeal joint swelling in psoriatic arthritis? Ultrasound findings and reliability assessment.

OBJECTIVES
To evaluate by ultrasound (US) the frequency and reliability of peritenon extensor tendon inflammation (PTI) and intra articular synovitis (IAS) in metacarpophalangeal joints (MCPj) of psoriatic arthritis (PsA) patients.


METHODS
27 PsA patients with clinical involvement of MCPj were consecutively included. Presence of PTI and IAS were evaluated by grey-scale (GS) and power Doppler (PD). Longitudinal and transverse 3-5 second videos of US examinations were recorded for reliability assessments by five readers. Consensus on positive US results was achieved when at least three readers agreed.


RESULTS
Clinical swelling was present in 60 joints whereas US detected IAS and/or PTI in 75 MCPj. GS PTI in at least one MCPj was found in 19 patients and 41 joints, concurring with clinical swelling in 30/41. GS IAS in at least one MCPj was found in 23 patients and 63 joints, concurring with clinical swelling in 37/63. The inter-reader reliability was good for PD PTI and moderate for GS PTI.


CONCLUSIONS
Our study identifies that both IAS and PTI cause MCPj swelling, where PTI is almost as frequent as IAS as a cause of swelling. The reliability of PTI is at least as good as for IAS.