Baseline Bone Erosions Are Prognostic Signs in RA

van Nies JA, van Steenbergen HW, Krabben A, et al., Evaluating processes underlying the predictive value of baseline erosions for future radiological damage in early rheumatoid arthritis. Ann Rheum Dis 2015;74:883-889 doi:10.1136/annrheumdis-2013-204659.

Zayat AS, Ellegaard K, Conaghan PG, et al., The specificity of ultrasound-detected bone erosions for rheumatoid arthritis. Ann Rheum Dis 2015;74:897-903 doi:10.1136/annrheumdis-2013-204864.

Mangnus L, Schoones JW, van der Helm-van Mil AHM. What is the prevalence of MRI-detected inflammation and erosions in small joints in the general population? A collation and analysis of published data.RMD Open 2015;1:e000005 doi:10.1136/rmdopen-2014-000005

Bone erosions found at a rheumatoid arthritis (RA) patient’s baseline exam are harbingers of future joint damage and more severe disease. As to why this is so, new studies offer only hints.

In the first article about, researchers in the Netherlands report their study of thousands of X-rays from 653 early RA patients. They found that those with 3 or more bone erosions went on to have almost 4 times more joint damage than those without erosions over the next 7 years.

Baseline erosions are an independent predictor of future radiologic damage and are associated with subclinical inflammation seen on magnetic resonance imaging (MRI), according to this analysis.

Studying a subset of patients with extremity MRIs as well as X-rays, the researchers found that 83% of non-swollen hand and foot joints with baseline erosions show evidence of subclinical inflammation on MRI -- compared with 25% of non-swollen joints without erosions.

What this means is unclear, however.

A mediation analysis of the same data (a search for a third explanatory variable) finds that baseline erosions cannot be explained by known predictors.

They do not appear to be mediated by localized or systemic inflammation, symptom duration, swollen joint counts, or the presence of autoantibodies (e.g., anti-citrullinated-peptide antibodies or rheumatoid factor).

The data come from two sets of consecutive patients in the Leiden Early Arthritis Clinic (EAC) cohort. The first set of patients (n=653), seen between 1998 and 2006, underwent baseline MRI and X-rays, and yearly radiographs.

A subset of patients (n=67) also had MRIs of metacarpal phalangeal (MCP) and metatarsophalangeal (MTP) joints.

Among the total group, 53% of the 3,256 hand and foot X-rays analyzed had 3 or more erosions.

Patients with erosions tended to be older, male, RF-positive, with higher erythrocyte sedimentation (ESR) rates.

What erosions are specific to RA?

Bone erosions are routinely used to classify RA, but there is no uniform definition of erosions and the underlying mechanism is not understood.

Joint erosions can also be seen on ultrasound, but they are not always specific to RA, say the authors of the second study.

They studied ultrasound images of hand, foot, and arm joints from 310 subjects: patients with RA (n=70), psoriatic arthritis (n=60), gout or osteoarthritis (n=60 each),and healthy volunteers (n=60).

Their analysis finds erosions are frequent in patients with joint diseases but not in healthy controls. Only larger erosions in selected joints are specific for RA.

RA patients also have more joints with extensive erosions compared to those with PsA.

Joint ultrasounds studied include the distal radius and ulna, the 2nd, 3rd and 5th MCP joints, the 1st and 5th MTP, and the 2nd and 3rd proximal interphalangeal (PIP) joints.

Larger erosions in the 2nd and 5rd MCP, 5th MTP joints and the distal ulna were highly specific for and predictive of RA (97.9% specificity, 41.4% sensitivity).

Erosions of any size in the 5th MTP joint were both specific and sensitive for RA (specificity 85.4%, sensitivity 68.6%).

Where to look?

Compounding the problem: Erosions and other signs of RA (such as synovitis) seen on MRI are frequently found in people without symptoms of the disease.

A systematic literature review of MRI studies that include symptom-free individuals reveals joint erosions in 33-52% among those without RA symptoms, and synovitis in 27%.

The prevalence of MRI-detected erosions increased with age, the researchers find.

The European League Against Rheumatism (EULAR) recommends MRI as valuable to improve RA diagnosis and to detect structural damage early on.

However, Mangnus and his coauthors conclude that “before MRI can be implemented in the diagnostic process, larger studies are needed to determine the degree and MRI features that are specific to RA.”