A common and well-documented feature of spondyloarthropathies is inflammation of the peripheral enthesis1. Ultrasound (US) imaging is useful when assessing enthesitis, and many investigators have described its features2,3.
A 50-year-old man with psoriasis developed morning stiffness, tenderness, and swelling of small joints in the hands asymmetrically during the last month. Clinical examination revealed tenderness and swelling of the proximal interphalangeal joints (PIP) of the second, third, and fourth fingers of the left and second finger of the right hand and the metacarpophalangeal (MCP) joints of the second and third fingers of the right hand. US of both hands was carried out to analyze the inflammation. The principal finding on US was swelling and hypoechogenicity of the enthesis of the extensor tendons on the involved PIP, with a medium-severe signal within the enthesis on power Doppler analysis, typical of enthesitis. Peritendinous edema and power Doppler signal at the second and third MCP joints were also found, as described by Gutierrez, et al4. The authors reported a high specificity of this sign for psoriatic arthritis even though the same US picture was present in patients with rheumatoid arthritis as described by Backhaus, et al5.
In our investigation, we focused on the enthesitis of the extensor digitorum tendons at the PIP (Figure 1). To our knowledge, this has not been documented as a US finding previously. Further studies are needed to expose enthesitis of the hands when differentiating rheumatoid arthritis from psoriatic arthritis.
The ultrasonographic aspect of enthesitis of the extensor tendon of the proximal interphalangeal joint in greyscale (panel 1) and with power Doppler scan (panel 2) and peritendinous inflammation of the extensor digitorum at the metacarpophalangeal (MCP) joint (panel 3). Note thickening of the insertional tract of the extensor tendon (ET, arrowheads, panel 1) and the presence of power Doppler signal within the tendon (panel 2). A small amount of liquid (*) and a slight synovial proliferation (s), without a Doppler signal, were also present. In panel 3, severe peritendinous inflammation of the extensor tendon at the MCP is visible, as described in patients with psoriatic arthritis4. Even in that case, mild synovial proliferation with a few spots of power Doppler signal was present.
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