Is the frequent sonographic anechoic area distally in metacarpophalangeal joints a sign of arthritis?

In clinical practice, ultrasonography (US) often reveals, in the dorsal scan, a small anechoic area distally in both inflamed and clinically non-inflamed metacarpophalangeal joints. This "distal anechogenicity in the metacarpophalangeal joint" (DAEM) might thus be scored false positively as arthritis. We aimed to investigate whether the DAEM is a sign of arthritis. We evaluated the prevalence of DAEMs in 24 non-arthritic subjects. We then compared the dimensions of the DAEM in 10 non-arthritic subjects with a DAEM and 7 consecutive rheumatoid arthritis (RA) outpatients, using 2-D and 3-D ultrasound. Furthermore, we dissected two fresh-frozen postmortem hand specimens after US. A DAEM was observed in the metacarpophalangeal 2 (MCP2) joints of 54% of the 24 non-selected non-arthritic individuals; in none of those did the joint exhibit a power Doppler signal. A DAEM was observed in 86% of the 7 RA patients. Dimensions of DAEMs did not statistically significantly differ between these groups. At 3-D imaging and dissection, the DAEM was found to be an extension of the metacarpophalangeal joint capsule. In conclusion, DAEMs occur frequently and are not a sign of arthritis, but are distal joint recesses. This should be taken into account when using current sensitive ultrasonographic scoring systems grading arthritis.