Ultrasound study supports deep Koebner mechanism in PsA pathology

March 15, 2018|Psoriatic Arthritis ICYMI

FROM ANNALS OF THE RHEUMATIC DISEASES

An ultrasonographic study describing the greater presence of thicker digital accessory pulleys in patients with psoriatic arthritis (PsA) than in those with only psoriatic skin disease, rheumatoid arthritis, or no pathology has lent more evidence for a “deep Koebner” response mechanism in the development of joint disease in people with psoriasis.

“The thicker pulleys in RA compared with HCs [healthy controls] might point towards a nonspecific effect of a chronic autoimmune tenosynovitis on the adjacent pulleys,” Ilaria Tinazzi, PhD, of the Sacro Cuore-Don Calabria Hospital, Verona, Italy, and her colleagues wrote in Annals of the Rheumatic Diseases. “However, the greater magnitude of pulley thickening in PsA, especially in the setting of dactylitis, suggests an intrinsic pathology in the pulley contributing to PsA-related tenosynovitis.”

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Dr. Tinazzi and her colleagues designed this study to investigate how PsA could be related to abnormal responses to physical stresses via a Koebner response in the skin and a deep Koebner response in the joints. Researchers enrolled 27 patients with PsA, 27 with RA, 23 with only psoriasis, and 19 healthy controls from two Italian centers. The volar aspects of the second to fourth digits of each patient’s dominant hand were imaged both transversely and longitudinally with ultrasound. Transverse and longitudinal measurements were taken of the A1 pulley at the metacarpophalangeal joint, and a dynamic exam determined the border between the A1 pulley and the flexor tendon. The A2 and A4 pulley thicknesses were analyzed during full extension. In total, 1,732 measurements were taken on 864 pulleys.

Dr. Tinazzi and her research team found that the pulleys in patients with PsA were thicker in every digit than they were in patients with RA and healthy controls, but pulley thickness also differed for each group of patients when compared with one another. Patients with RA had thicker pulleys than did healthy controls, particularly in the A1 pulley, but showed no differences in the A2 and A4 pulleys of the second and fourth digit. Even patients with only psoriasis had thicker pulleys than did the healthy controls. Patients with PsA exhibited thicker A1 and A4 pulleys, compared with patients with only psoriasis, while A2 pulleys displayed no statistical difference. Among PsA patients, 165 of 243 (68%) pulleys were thickened, whereas only 41 of 243 (17%) were thickened among RA patients (P less than .001). A multiple-regression analysis revealed that only PsA was associated with the number of thickened pulleys (odds ratio, 4.8; 95% confidence interval, 3.3-6.3; P = .001).