Targeted ultrasound of the fifth metatarsophalangeal joint in an early inflammatory arthritis cohort.

OBJECTIVE: To determine whether targeted ultrasonographic (US) imaging of the fifth metatarsophalangeal (MTP) joint, compared with radiographs, could aid in the early diagnosis of rheumatoid arthritis (RA) by identifying erosions sooner in early inflammatory arthritis. Radiographic erosion in RA is a late indication of poor prognosis. The earlier detection of erosion may facilitate the timely initiation of disease-modifying antirheumatic drug therapy, particularly in patients with undifferentiated synovitis.
METHODS: Patients presenting with synovitis for the first time were invited to participate. Each patient underwent laboratory tests, radiographs of the hands and feet, and US imaging of both fifth MTP joints.
RESULTS: Thirty patients (22 women) took part in the study. Seventeen patients (57%) had RA, and 13 (43%) had undifferentiated arthritis (UA). The mean +/- SD time taken to scan both fifth MTP joints was 10.9 +/- 4.4 minutes. Ten patients (33%) had US evidence of synovitis associated with a positive power Doppler (PD) signal (P = 0.04). Seven patients (23%) had radiographic erosions of the fifth MTP joint, and 17 patients (57%) had US evidence of fifth MTP joint erosions (P = 0.01). A positive PD signal at the fifth MTP joint was seen in 9 of 17 patients with RA and 1 of 13 patients with UA (P = 0.02). Patients with a definite diagnosis of RA were more likely to have fifth MTP joint erosions (11 [65%] of 17) compared with UA (6 [46%] of 13).
CONCLUSION: Targeted US is a rapid and useful tool in detecting erosive disease in early inflammatory arthritis. It gives a better indication of disease severity and prognosis compared with routinely available laboratory tests, even in the absence of a definite diagnosis.