We read with interest the pictorial essay on ultrasonography of bone erosions by Grassi and colleagues.1 The presented site-specific comparison of radiographic and sonographic imaging of metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joint sites in rheumatoid subjects suggests strongly a homology of the erosive lesions, as visualised by these different imaging modalities. A recently published study by an independent group,2 comparing radiographic and sonographic imaging of MCP joints in patients with rheumatoid arthritis (RA) supports this impression. The same study observed magnetic resonance imaging (MRI) changes corresponding to specific sites at selected radiograph-negative joints that had sonographic erosions, and found (depending on disease duration) 3.4- to 6.5-fold more erosions with ultrasound than with radiography.

In our experience, based on pilot data on rheumatoid patients with a disease duration of up to six years, sonographic erosions could be shown in half of all 5th MTP joints examined. Fifteen patients with RA, according to standard criteria,3 (median age (range) 48 (23–78) years; eight female; median disease duration (range) 13 (1.5–72) months; 12 rheumatoid …