Background The thumb base is frequently involved in patients with hand osteoarthritis (OA), resulting in osteophytes and cartilage loss. Radiography is the most commonly used imaging modality to evaluate structural OA signs, however it is insensitive especially due to overprojection. Magnetic resonance imaging (MRI) could be a valuable alternative, however a standardized scoring method for thumb base MR images did not exist until recently OMERACT developed the thumb base OA MRI scoring system (TOMS)1.
Objectives Our aim was to investigate the validity of the new TOMS by comparing TOMS scores with radiographic scores.
Methods Two hundred consecutively included patients (83.5% women, median age 60.5 years) diagnosed with primary hand OA in secondary care, who had both a dorsopalmar radiograph of the right hand and a MRI scan of the right thumb base taken at baseline, were studied. T1- and fat suppressed T2-turbo spin weighted sequences were performed in axial and coronal planes on a 1.5 Tesla extremity MRI unit. Radiographs of the first carpometacarpal (CMC1) and scaphotrapeziotrapezoid (STT) joints were scored using the OARSI atlas (osteophytes and joint space narrowing [JSN] in CMC1: 0–3 and STT: absent/present) by one reader with good intra-reader reliability, blinded for clinical and MRI data. MR images were scored using TOMS (osteophytes in CMC1: 0–6 and STT: 0–9; cartilage space loss [CSL] for both joints: 0–3) by two readers, blinded for clinical and radiographic data, with good intra- and inter-reader reliability. For further analysis we used the average of both readers, rounded down to the nearest integer. To study validity, the distribution of the TOMS scores for osteophytes and CSL were compared for the different radiographic stages for osteophytes and JSN, respectively.
Results On MR images osteophytes were detected in the vast majority of thumb bases (CMC1 n=172; STT n=102). The score of TOMS increased with more severe radiographic stages (see figures). However, the number of patients without any osteophytes in both CMC1 and STT was considerably lower for TOMS (n=19) than for the OARSI (n=106) scoring. A similar difference was apparent for absence of CSL (n=82) versus JSN (n=108) in both CMC1 and STT. Patients with isolated STT osteophytes were quite rare for both TOMS (n=9) and the OARSI (n=5) scoring. The most prominent discrepancy between TOMS and OARSI sensitivity was found for osteophytes: an additional 168 joints (CMC1 n=84; STT n=84) were found positive with TOMS, while only 1 OARSI-positive CMC1 scored negative with TOMS.
Conclusions Scores of osteophytes and cartilage loss assessed on MR images by TOMS were correlated with radiographic scores, indicating good validity of the TOMS. Furthermore, the frequencies of joints with osteophytes and cartilage loss assessed on MR images were higher compared to those on radiographs, suggesting high sensitivity for the TOMS.
Kroon FPB, Conaghan P, Foltz V, et al. Development and reliability of the OMERACT thumb base osteoarthritis MRI scoring system. J Rheumatol. 2017; in press.
Disclosure of Interest None declared
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