Synovitis Confirmed as Prognostic in Hand Osteoarthritis, Regardless of Subtype

Patients with osteoarthritis (OA) of the hand face the same risk of structural progression when synovitis is present in the first carpometacarpal (CMC1) joint versus the interphalangeal joints, results of a prospective cohort study indicated.

Among 201 hand OA patients followed for an average 3.4 years, those with high-grade synovitis in the CMC1 joint at baseline had 9.3-fold greater odds of clinically relevant radiographic progression (95% CI 2.2-39.6) compared with patients without synovitis, according to Marthe Gløersen, MD, of Diakonhjemmet Hospital in Oslo, Norway, and colleagues. This was considered comparable to the odds ratio of 23.4 (95% CI 10.4-52.9) found with baseline synovitis in predominantly interphalangeal OA, in light of the broadly overlapping confidence intervals.

Writing in RMD Open, Gløersen’s group explained that CMC1 (at the thumb base) and interphalangeal (the more distal joints in the thumb and fingers) OA have been regarded as separate subtypes of hand OA with potentially different clinical courses.

In general, synovitis — inflammation within the joint — is a strong risk factor for progression in hand OA. But different individuals can show a variety of phenotypes, with pain and reduced mobility affecting certain joints but not others. “Currently, it remains unknown whether synovitis has similar prognostic significance in the CMC1 and interphalangeal joints,” the researchers wrote.

To answer this question, Gløersen and colleagues analyzed data from the so-called Nor-Hand study, a prospective observational cohort of patients with hand OA at Diakonhjemmet Hospital. They were enrolled in 2016-2017, with a second visit in 2019-2021. Synovitis was assessed with ultrasound and MRI scans at baseline; structural status was determined from x-rays both at baseline and at the follow-up visit. The latter was classified on the standard Kellgren-Lawrence scale of 0-3, with joint space narrowing and erosions also quantified.

For the current analysis, the primary endpoint of progression was moving up a grade on the Kellgren-Lawrence scale.

Mean patient age was 61 and close to 90% were women. In total, the 201 patients had assessments of 397 CMC1 joints and 3,608 interphalangeal joints. Some 12% of patients had OA only in the CMC1 joint and for 47% it was exclusive in interphalangeal joints; the remainder had some involvement in both. At baseline, about half of both types of joints had Kellgren-Lawrence scores of 2 or 3, and a similar proportion showed some degree of osteophytes and joint space narrowing, but very few had erosions.

Any degree of synovitis in either joint type at baseline was predictive of radiographic progression, but the associations grew stronger with each grade of grey-scale synovitis severity. At grade 1, odds ratios of 2.2-2.8 were seen, compared with synovitis-free joints, versus 9.3-23.4 for joints with grade 3 synovitis. Similar patterns were seen for baseline osteophytes and joint space narrowing, although for the latter, the associations were statistically significant only for interphalangeal joints (and the point estimates were much greater).

Gløersen and colleagues also analyzed power Doppler ultrasound readings at baseline. These, too, were generally predictive of future progression, but more of these analyses fell short of statistical significance, in part because fewer patients showed high-grade inflammation with this method versus grey-scale ultrasound.

What remains a mystery, the researchers noted, is whether attempts to treat synovitis early can reduce risk for progression, or whether this may vary by joint type. “The effect of intra-articular corticosteroid injections varies across joint groups,” they wrote. “While a randomized controlled trial in interphalangeal OA demonstrated reduced pain during movement, randomized trials in CMC1 OA found no pain benefit compared with intra-articular saline or local anesthesia.” At least one ongoing trial, dubbed PICASSO, is now evaluating steroid treatment in CMC1 joints to relieve pain, but structural outcomes are not a focus. Indeed, an effective disease-modifying therapy for OA of any type, other than joint replacement, has yet to be found.

Limitations included the relatively small number of CMC1 joints evaluated in the study, which reduced the statistical power for some analyses. It was also a single-center study in one high-income, largely white region that may not be representative of patients in routine care elsewhere.