Symptomatic psoriatic dactylitis is associated with ultrasound determined extra-synovial inflammatory features and shorter disease duration

Objectives: To explore the link between ultrasonographic features of dactylitis in psoriatic arthritis (PsA) and symptoms, digital tenderness and duration of dactylitis. Methods: Forty-eight cases of PsA dactylitis were investigated using high frequency ultrasound (US) both in grey scale (GS) and Power Doppler (PD), evaluating the presence and the degree of flexor tenosynovitis, peri-tendinous oedema, subcutaneous PD, extensor tendon involvement, GS synovitis and intra-articular PD signal (PDS) of the involved digits. Patients were compared according to the presence of local pain and digital tenderness, the duration of dactylitis and the concomitant treatment. Results: The presence of pain/tenderness was positively associated with US GS flexor tenosynovitis of grade > 2 (p < 0.001), PD-flexor tenosynovitis (p < 0.001), peri-tendinous oedema (p < 0.001) and subcutaneous PDS (p < 0.001); moreover, it was negatively associated with GS synovitis (p < 0.001) and intra-articular PD (p < 0.001). The same positive and negative association with US findings were found comparing patients with duration of dactylitis shorter or longer than the median (24 weeks) (p < 0.001 for all comparisons). Conclusions: Pain and digital tenderness are linked to dactylitis duration and earlier lesions are associated with extra synovial inflammatory changes. These findings suggest a hitherto unappreciated extra synovial basis for symptoms in PsA dactylitis.