Background Ultrasonography (US) has better sensitivity than clinical evaluation for the detection of synovitis in early inflammatory arthritis. The clinical importance and fate of undifferentiated synovitis in patients with polyarthralgia are still unknown.¹

Objectives To identify clinical outcome of undifferentiated synovitis detected by ultrasound in patients with polyarthralgia and to identify variables that can predict differentiation into specific type of arthritis.

Methods New patients with polyarthralgia and undifferentiated synovitis were followed by clinical and ultrasound examination in the period between June 2015 to June 2017. Undifferentiated synovitis was defined as ultrasound detected synovial hypertrophy in cases in which no definitive diagnosis can be made.

Baseline assessments included: clinical examinations of complaining joints, laboratory investigations (CBC, ESR, CRP, RF, ACPA, ANA) and ultrasonographic evaluation of fifty joints (DIPs, PIPs, MCPs, wrists, elbows, shoulders, hips, knees, ankles and MTPs)

Follow ups were every 6–8 weeks until remission of synovitis or a definite clinical diagnosis was reached. Remission was defined as absence of a previously US detected synovitis in two consecutive follow-ups eight weeks apart.

Patients were received treatment according to the opinion of the treated rheumatologist who had a full data about clinical, laboratory and ultrasonographic data. Multivariate logistic regression analysis was used to identify predictors of remission, RA, PsA and continuation as undifferentiated synovitis.

Results 174 patients (88.6% women, mean age 43.2±14.2 years (range 17–75)) were included.

Duration of follow up period ranged from 3 to 38 months (mean 11.4 months)

Final diagnoses were as follow; complete remission in 73 (41.7%) cases, rheumatoid arthritis (RA) in 20 cases (11.4%), psoriatic arthritis (PsA) IN 10 cases (5.7%), spondyloarthropathy (SPA) in 11 cases (6.1%), sarcoidosis in 4 cases (2.3%), osteoarthritis (OA) in 10 cases (5.7%) and 46 cases (26.4%) continued as undifferentiated synovitis up to the end of the follow up period.

Remission of undifferentiated synovitis was associated with significantly older mean age, acute onset and absence of PD activity (OR 1.92, 1.95 and 1.86 respectively).

Development of RA was associated with chronic onset, positive rheumatoid factor, positive ACPA and US detected synovitis in more than three joints (OR 1.91, 1.75, 1.92 and 1.79 respectively). All patients with final diagnosis of RA had US detected synovitis in wrist joint with increased PD activity. PsA was associated with chronic onset, PD activity, bilateral knee synovitis, negative RF and ACPA (OR 1.84, 1.83, 1.94, 1.88 and 1.79 respectively). Cases with significantly younger mean age and shorter disease duration completed with undifferentiated synovitis (OR 1.92 and 1.87).

Conclusions In our study, more than halve of cases of ultrasound detected undifferentiated synovitis in patients with polyarthralgia differentiated into specific type of arthritis during the follow up period. older age and acute onset of symptoms are associated with remission while positive rheumatoid factor, positive ACPA, US detected synovitis in more than 3 joints including wrist joints are associated with development of RA. Bilateral knee synovitis are in favour of PsA and OA.

Reference [1] Zufferey P, et al. Joint Bone Spine2017May;84(3):299–303. doi:10.1016/j.jbspin.2016.05.011

Disclosure of Interest None declared