Background Joint erosions in RA correlate with structural damage progression and functional capacity. Therefore, detection and the follow-up of erosions are of paramount importance for RA diagnosis, monitoring and determining of prognosis. The 5th MTP is usually the first and most commonly destructed joint in RA. Ultrasound (US) is a useful and as good tool as MRI to detect 5th MTP erosions especially in early RA patients. Although a few MRI studies revelaed that most of the MTP erosions were located at the plantar aspect of the joint, it is unknown whether plantar or dorsal or lateral plane US better detects 5th MTP erosions.
Objectives To determine the best ultrasonographic plane for detection of 5th MTP joint erosion in RA patients and to assess clinical characteristics of patients with 5th MTP erosions.
Methods The 5th MTP of 92 feet of 48 RA patients were evaluated by B-mode and Power- Doppler US for signs of erosion. US images were obtained from 3 different aspects, the dorsal, lateral and the plantar surface of the foot, in longitudinal and tranverse planes. The presence of erosion was determined according to OMERACT definition. Patients were also assessed clinically (tender/swollen joint count, DAS28, HAQ scores) along with disease characteristics. Each erosion in each aspect were recorded seperately.
Results The study cohort consisted of 48 RA patients (F/M=35/13, mean age 50.7±12.3 years, mean DAS28 score 4.04±1.47, HAQ score 0.93±0.88) with mean disease duration of 8.2±7.3 years. RF and anti- CCP positivity were 66.7% and 60.4%, respectively. The 5th MTP erosions were detected in 35 of 48 patients (72.9%) and 62 of 92 feet (67.4%). Of the erosions 15 (16.3%) were observed at dorsal plane whereas plantar and lateral planes revelaed majority of the erosions, 53 (57.6%) and 52 (56.5%), respectively. In 26 feet (28.3%), erosions were observed on both plantar and lateral planes, in 15 feet (16.3%) erosions were observed in all three planes. None of the patients had erosion just in dorsal plane examination of the 5th MTP. The presence of 5th MTP erosion in plantar aspect of foot was significantly higher than both lateral and dorsal aspect (P<0.0001, P=0.002, respectively). Patients with dorsal erosion had significantly higher disease duration (13.8 years vs 6.5 years, P=0.005). Patients with erosion in any aspect have similar disease characteristics including, RF, anti-CCP positivity, disease duration, HAQ scores and current biologic requirement, when compared to patients without erosion.
Conclusions The 5th MTP erosions in RA patients can be better detected with plantar plane US than dorsal and lateral aspect evaluations. These data also indicate that dorsal aspect US of foot may miss erosions in early disease and insufficient when performed solely.
Disclosure of Interest None declared
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