Ultrasound imaging for the rheumatologist XXXIII. Sonographic assessment of the foot in early arthritis patients

Objectives. To investigate the ability of ultrasonography (US) to detect synovitis in metatarsophalangeal joints (MTP) in patients with suspicion of early arthritis, and to discriminate between diagnoses. Methods. Patients referred to early arthritis clinics for differential diagnosis were enrolled, and clinical and laboratory measures were recorded. Ultrasonography of MTPs was performed searching for synovial hypertrophy (SH), joint effusion (JE) and power Doppler (PD), graded from 0 to 3 on a semi-quantitative scale. Patients were classified according to definite classification criteria, or as undifferentiated arthritis or non-inflammatory pathology. US findings were compared across different diagnoses and diagnostic accuracy was calculated taking clinical diagnosis as reference. Results. Out of 427 patients (71% rheumatoid arthritis (RA), 20% undifferentiated arthritis (UA), 15% spondyloarthritides (SpA), 13% non-inflammatory), 307 (71.9%) showed SH, 120 (25.5%) JE, 77 (18.0%) PD. RA patients had median JE, SH and PD scores significantly higher than non-inflammatory and other diseases. Patient with UA and SpA had higher scores of SH and JE compared to non-inflammatory, no significant differences were present among different diagnosis. In RA, SH and JE were more frequently detected in the second MTP, and PD in the fifth. Crystal-related arthritis showed a tendency towards a more frequent involvement of the first MTP. The diagnostic accuracy of single US measures was moderate, but the detection of a PD of 2 or more provided a high specificity for the diagnosis of RA. Conclusions. US can be used as additional information in patients evaluated in an early arthritis setting. High scores of JE, SH and PD, together with the pattern of involvement are suggestive of RA.