Background/Purpose: Dactylitis (DACT) is defined as diffuse swelling of the digit and is included in the ASAS criteria for spondyloarthritis. It is a hallmark feature of psoriatic arthritis (PsA), occurring in 16-24% of cases. One of the main problems with the definition of dactylitis is the existence of a chronic non-tender form. The lack of tenderness suggests inactive disease, but subclinical inflammation may exist. Objective. To assess ultrasound (US) pathological lesions in dactylitic digits of patients suffering from PsA.

Methods: Consecutive PsA patients suffering from at least one DACT in feet or hand were included. The presence of DACT was diagnosed at clinical examination. At US examination, the entire DACT digit was scanned both on dorsal and palmar/plantar sides. The following ultrasound pathological lesions were scored: soft tissue thickness and edema, synovitis of MCP, PIP and DIP joints, inflammatory involvement of both flexor (tenosynovitis) and extensor (paratenonitis) tendons, nail bed vascularity, synovio-entheseal complex at DIP level, enthesitis of flexor tendon, intra-articular and extra-articular bone proliferation. Gray-scale (GS) and power-Doppler (PD) synovitis and tenosynovitis were assessed according to OMERACT scores (0-3). Nail bed vascularisation was scored 0 to 3. The other US lesions were scored 0 (absent) or 1 (present), both in GS and PD. The standard (HAQ) questionnaire, tender and swollen joint count, tenderness of DACT, global disease activity scored by physician and by patient were assessed in all patients.

Results: Twenty-eight DACT from 17 consecutive patients (8 men and 9 women) suffering from PsA were examined by US. Mean age was 43.3±11.2 years. Nine patients presented with hand DACT and 8 patients with foot DACT. Ten patients had single DACT. Seven patients presented with multiple DACT: 3 simultaneous DACT in 4 patients and 2 simultaneous DACT in 3 patients. Seven patients were on non-biologic DMARD, 2 patients were on combined therapy with biologics, one patient was on biologic monotherapy and 7 patients were DMARD naïve. Soft tissue thickness was present in all DACT. Synovitis of at least one joint was present in all DACT (28/28). The MCP synovitis was present in 75% (21/28) of DACT, PIP synovitis in 60% (17/28) of DACT, and DIP synovitis in 43% (12/28) of DACT. Inflammatory involvement of tendons was observed in 75% (21/28) of DACT: more flexor than extensor tendons were involved. Enthesitis was present in 68% (19/28) of DACT. Nail bed hypervascularisation (PD grade 3) was present in 14% (4/28) of DACT. Bone proliferation was present in 46% of DACT (13/28). A significant association between tenderness and the presence of PD and/or edema in the soft tissue was observed (p<0.01). The frequency of synovitis, tenosynovitis and enthesitis did not differ significantly between tender and non-tender DACT.

Conclusion: We show that US pathological lesions in DACT are more heterogeneous than previously reported. In particular, DACT is characterized by simultaneous involvement of joints, tendons and soft tissue. A significant amount of joint, tendon and entheseal inflammation persists in non-tender DACT. Tenderness tends to be associated with the presence of edema and/or PD inside the soft tissue, but larger samples are required to confirm these results. The impact of current treatments on inflammation might differ according to joint, tendon or entheseal level involved in DACT.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/which-are-the-ultrasound-lesions-underlying-dactylitis/