GLASGOW, SCOTLAND — Involvement of the distal interphalangeal joint is a common feature of both psoriatic arthritis and osteoarthritis, but a new study using high-resolution magnetic resonance imaging has shown that the local microanatomical environment in psoriatic arthritis is quite distinct, according to Dr. Ai Lyn Tan.
The study included 10 patients with psoriatic arthritis (PsA), 10 with osteoarthritis (OA), and 10 normal controls. The distal interphalangeal joint structures, including ligaments, tendons, and entheses, were imaged using a 1.5-T MRI scanner with a 23-mm diameter microscopy coil and producing T-weighted spin-echo images, Dr. Tan wrote in a poster session at the annual meeting of the British Society for Rheumatology.
PsA was characterized by significant inflammation of ligaments and tendons, along with involvement of the corresponding entheseal insertions. Extracapsular enhancement and nail bed changes were striking, as was diffuse bone edema, particularly of the distal phalanx, she reported.
This condition was present in 80% of the PsA patients, often without cartilage damage.
“It appears that the ligament and extensor tendon entheses are the epicenter of the inflammatory response in PsA, with diffuse involvement of adjacent structures,” observed Dr. Tan of the Academic Unit of Musculoskeletal Disease, University of Leeds (England).
Findings among patients with OA also included more ligament and entheseal changes than among the normal controls, but there was significantly less contrast enhancement, compared with PsA. The OA joints were characterized by less soft-tissue swelling, and with degenerative changes such as loss of cartilage, usually at the volar aspect, she noted.
Osteophytes also were present in some OA joints, along with focal bone edema at the tendon entheses.
These observations suggest that, while in PsA inflammatory changes are prominent in ligaments, tendons, and adjacent bone, changes in the entheseal insertions appear to be primary, Dr. Tan suggested. Similar changes are present in OA, but they are much less marked.
“This study in patients with PsA adds further weight to the argument that enthesitis is the unifying concept in patients with true PsA,” Dr. Tan also wrote (Arthritis Rheum. 2006;54:1328–33).