Spondyloarthropathies
Abstract #2058: The Relationship Between the Extensor Tendon Enthesis and Distal Interphalangeal Joint Disease in Psoriatic Arthritis: High-Resolution MRI and Histological Study
Authors: Tan, et. al.
Purpose: It has long been recognized that psoriatic arthritis is distinct among the inflammatory articular conditions in that it involves inflammation of the DIP joint. The reason for this has remained elusive. Using high-resolution magnetic resonance imaging (hrMRI) this study aims to better understand the anatomy of inflammation at this site.
Methods: High-resolution MRIs were obtained in 30 patients (10 PsA, 10 osteoarthritis, and 10 normal volunteers). In each of these subjects, the following structures were evaluated: DIP joint capsule, tendon enthesis, nail bed, and nail root.
Results: Nail involvement in the form of oncholysis was seen in 8 of 10 patients with PsA. There were no abnormal nail findings in the patients with osteoarthritis or the normal controls. In 8 out of 10 patients with PsA, there was evidence of inflammation of the enthesis extending to the distal phalanx seen with hrMRI. This finding was seen in only 4 of 10 cases of OA, with much less inflammation. In a separate histological study using ten normal cadavers, it was determined that the DIP joint capsule is intimately linked to the nail complex. Thus, the investigators hypothesize that DIP involvement in patients with PsA stems not from capsular inflammation at that joint, but from enthesitis involving the extensor tendons.
Comment: DIP involvement, as well as enthesitis in the form of the “sausage digit,” has always been a “calling card” to PsA. By using advanced techniques of hrMRI, we are provided with a very plausible explanation for DIP swelling that is seen in PsA. Unlike the synovial inflammation that occurs at MCP and PIP joints of RA, the DIP abnormalities in these patients with PsA appear to be due to the tendon inflammation which is a hallmark of PsA as well as other members of the spondyloarthritis family.