Introduction: To assess clinical and ultrasound effectiveness of steroid injection (local treatment, LT) into the digital flexor tendon sheath for the treatment of psoriatic dactylitis compared to systemic treatment (ST) alone. Methods: In this observational, multicentre, prospective study, 88 cases of symptomatic hand dactylitis were evaluated clinically and sonographically by high-frequency ultrasound (US) probe in both greyscale (GS) and power Doppler (PD). The presence of flexor tenosynovitis (FT), soft tissue oedema (STO), peritendon extensor inflammation and synovitis was assessed (including DACtylitis glObal Sonographic—DACTOS—score) before treatment, at 1-month (T1) and 3-months (T3) follow-up. LT was proposed to all patients. Patients refusing LT were treated with oral NSAIDs. Patients continued the same baseline csDMARDs and/or corticosteroid therapy during the whole follow-up period. US response was defined for DACTOS score < 3 and US remission for DACTOS score = 0. Results: At T3 evaluation the ST group showed a significantly higher persistence (grade > 1) of FT and STO (p < 0.001 for all) and MCP synovitis (p = 0.001). US remission was achieved only in the LT group (at T3 31% vs. 0, p < 0.001). The percentage of patients with DACTOS < 3 was significantly greater in the LT group compared with ST group, at both T1 (49% vs. 5%, p < 0.001) and T3 evaluation (76% vs. 7%, p < 0.001). In multiple conditional logistic regression analysis, the only factor associated with US remission was LT (T3 odds ratio = 41.21, p < 0.001). Conclusions: US confirmed the effectiveness of steroid injection for dactylitis by demonstrating that it involves the resolution of extra-articular inflammation, in particular FT and STO.
