Rheumatology Advance Access originally published online on July 11, 2006
Rheumatology 2007 46(2):253-256; doi:10.1093/rheumatology/kel214
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The relationship between the extensor tendon enthesis and the nail in distal interphalangeal joint disease in psoriatic arthritis—a high-resolution MRI and histological study
1Academic Unit of Musculoskeletal Disease, Chapel Allerton Hospital, Leeds LS7 4SA, 2School of Biosciences, Cardiff University, Cardiff CF10 3US, 3Department of Radiology, Chapel Allerton Hospital, Leeds LS7 4SA, 4Academic Unit of Medical Physics, University of Leeds, Leeds LS1 3EX and 5Department of Rheumatology, Calderdale Royal Hospital, Salterhebble, Halifax HX3 0PW, UK
Correspondence to: Prof. Dennis McGonagle, Academic Unit of Muscoskeletal Disease, Chapel Allerton Hospital, Chapeltown Road, Leeds LS7 4SA, UK. E-mail: d.g.mcgonagle{at}leeds.ac.uk
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Abstract |
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Objectives. Diffuse swelling of the distal interphalangeal (DIP) joint beyond the joint margin is a common feature of arthritis in psoriatic arthritis (PsA). The purpose of this study was to explore the microanatomical basis for the inflammation and nail disease in PsA using a combined high-resolution magnetic resonance imaging (MRI) and histological studies.
Methods. High-resolution MRIs of the DIP joint were obtained in 30 subjects [10 PsA, 10 osteoarthritis (OA) and 10 normal volunteers]. The relationship between the DIP joint capsule and associated tendon enthesis and the nail bed and root were evaluated. Histological studies to define the relationship between the normal cadaveric DIP joint capsule and the nail root were performed on the middle and ring fingers of 10 dissecting room cadavers.
Results. On MRI, the dorsal capsular enthesis was the epicentre of an inflammatory reaction. This extended to involve the soft tissues adjacent to the nail in 8 of 10 cases in PsA, but only 4 of 10 cases in OA where the inflammation is less intense and in none of the normal fingers. The DIP joint capsule was intimately linked with the nail complex on histology, with the dorsal, volar and lateral aspects of the nail bed being ensheathed in fibres extending from the entheses.
Conclusion. The study suggests that the extended nature of the enthesis organ associated with the DIP joint may explain the diffuse nature of the inflammatory response around the nail in PsA. Therefore the nail is as much an integral part of the enthesis organ as it is of the skin, which has implications for a better understanding of the disease.
KEY WORDS: Psoriatic arthritis, Distal interphalangeal joint, Magnetic resonance imaging, Histology, Enthesis, Nail, Extensor tendon
Submitted 26 February 2006;
revised version accepted 16 May 2006.
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