Deep Dive Into the Causes of Dactylitis

Dactylitis develops in up to 40% of patients with psoriatic arthritis (PsA). Previous imaging analyses point to flexor tenosynovitis, soft-tissue edema, joint synovitis, and osteitis as the causes of dactylitis.

Tinazzi and colleagues in Italy and Canada point out that more recently enthesitis has been implicated in the pathogenesis of spondyloarthritis and PsA in particular.¹ Studies have shown entheseal changes in the digital pulleys at flexor tendons in dactylitis, where inflammation in the fibrocartilage may become thickened in triggered fingers.

Previous work has implicated physical stress with Koebner response in skin and a “deep Koebner” response in the joints involving areas of high physical stress, such as the small digital pulleys in PsA.

Koebner phenomenon, or Koebnerization, is named after the German dermatologist Heinrich Koebner, who found that skin in people with psoriasis which had become traumatized following an injury often developed a psoriatic lesion in the area. The authors wondered whether this mechanical stress could be extrapolated to the “deep” tendons and joints in PsA.

The authors investigated the digital pulleys in patients with PsA and compared them with joints in patients with rheumatoid arthritis (RA) and psoriasis versus healthy controls. They recently presented their findings in Annals of the Rheumatic Diseases.

The study
The authors examined the A1, A2, and A4 pulleys in 27 patients with PsA, 27 patients with RA, 23 patients with psoriasis without arthritis, and 19 healthy controls. Clinical assessments were blinded and joints examined with ultrasound.

The results
• Patients with PsA had thicker pulleys in every digit compared with those in all other groups.

• Patients with psoriasis but not arthritis had thicker pulleys than healthy controls.

• Patients with RA had thicker pulleys than healthy controls.

• More pulleys were thickened in the PsA group (165/243, 68%) than in the RA group (41/243, 17%; P < .001).

• Only the second-digit A1 pulley was found thicker in patients who had previous dactylitis.

Please click below for Implications for Clinicians.

Implications for clinicians
• Pulleys are thickened in subjects with PsA when compared with both subjects with RA and healthy subjects.

• A similar inflammatory synovitis may be in play with RA on a less severe scale when compared with PsA.

• Areas subjected to high physical stress seem to exhibit a “deep Koebner” phenomenon and are thickened in PsA.

• This phenomenon supports the idea of an early biomechanical change in tendon function leading to dactylitic tenosynovitis.

• These findings point to tissue damage as a cause of synovitis and dactylitis rather than inflammation.

References:

1. Tinazzi I, McGonagle D, Sibel Z Aydin, et al. Deep Koebner’ phenomenon of the flexor tendon-associated accessory pulleys as a novel factor in tenosynovitis and dactylitis in psoriatic arthritis. Ann Rheum Dis. Published online: March 6, 2018. doi:10.1136/annrheumdis-2017-212681.