Background Hand OA affects the interphalangeal (IP) and thumb base joints (first carpometacarpal [CMC1] and scaphotrapeziotrapezoid [STT]). Much is still unknown about the pathophysiology of thumb base OA. Magnetic resonance imaging (MRI) studies have led to new insights in IP OA, but in absence of a scoring system thumb base MRI studies are lacking.
Objectives Investigate the prevalence of MRI synovitis and BMLs in the thumb base, and their association with pain, using the novel OMERACT thumb base OA MRI scoring system (TOMS)1.
Methods Cross-sectional data of the Hand OSTeoArthritis in Secondary care (HOSTAS) study, including consecutive patients diagnosed by their treating rheumatologist with primary hand OA, were used. Patients with an MRI of the right thumb base at baseline were included in the analysis. MRIs were scored by two readers using the TOMS for synovitis and bone marrow lesions (BMLs) in the CMC1 and STT joints (grade 0–3). BMLs were evaluated in the proximal and distal joint parts separately, resulting in a 0–6 and 0–9 sum score for CMC1 and STT, respectively. Pain on palpation of the thumb base was assessed by trained research nurses. Hand radiographs were assessed for presence of osteophytes in the CMC1 and STT joints. Associations between MRI lesions and thumb base tenderness were analysed using logistic regression, presented as odds ratios (ORs) with 95% confidence intervals (CIs), stratified for absence or presence of radiographic osteophytes. For the analyses synovitis and BML scores were aggregated into a dichotomous total thumb base involvement score (0–1 in both joints vs ≥2 in at least one joint).
Results 85 out of 202 patients (84% women, mean age 60.1 years) reported pain on palpation in the thumb base. Synovitis was seen in both thumb base joints (CMC1 42%, STT 37%), although prevalence of grade 2–3 synovitis was low in both the CMC1 (16%) and STT (14%). BMLs were present in CMC1 and STT in 54 and 53%, respectively, with 18 and 21% having a sum score of 2–3, and 16 and 7% a sum score ≥4. In absence of radiographic osteophytes, presence of synovitis or BMLs in either thumb base joint was not statistically significantly associated with thumb base tenderness (ORs 1.9 [95% CI 0.6–6.4] and 1.5 [0.5–4.3], respectively). However, in absence of synovitis or BMLs, radiographic osteophytes and pain were associated, with increasing ORs when MRI lesions were additionally present (Table). Similar results were found for self-reported thumb base pain (not shown).
Conclusions Synovitis and BMLs are present in the thumb base, although severe MRI lesions were uncommon. Prevalence of synovitis was similar in the CMC1 and STT joints, although higher BML scores were more frequently seen in CMC1. Radiographic osteophytes seemed more important in predicting thumb base tenderness than MRI inflammation alone. Combined presence of radiographic osteophytes and MRI lesions had a small additive effect. These findings are in contrast to results from IP OA studies, supporting thumb base OA as a distinct hand OA subset. It might also explain why trials investigating intra-articular corticosteroids in thumb base OA have led to equivocal results.
Kroon F, Conaghan P, Foltz V, et al. J Rheumatol 2017 (in press).
Disclosure of Interest None declared