title: Plasma YKL-40: a potential biomarker for psoriatic arthritis?
abstract: BACKGROUND
  Plasma YKL-40 is an inflammatory biomarker. No useful biomarker exists in patients with psoriasis or psoriatic arthritis.
  
  
  OBJECTIVE
  To measure YKL-40 and high-sensitivity C-reactive protein (hs-CRP) in patients with psoriasis or psoriatic arthritis before and during treatment.
  
  
  METHODS
  In 48 patients with psoriasis, we measured YKL-40, hs-CRP and Psoriasis Area and Severity Index (PASI) at inclusion and in a subgroup of 14 patients, we repeated the measurements after four to six weeks of methotrexate treatment. In 42 patients with psoriatic arthritis, we measured YKL-40 and hs-CRP at inclusion and during 48 weeks of adalimumab treatment. The patients with psoriatic arthritis were divided into responders and non-responders.
  
  
  RESULTS
  In patients with psoriasis, the baseline median PASI score was 10.8 and baseline YKL-40 was 45 μg/L. Seventeen per cent had elevated plasma YKL-40 compared with healthy subjects. Baseline PASI and YKL-40 were not correlated (rho = 0.14, P = 0.347) and YKL-40 and hs-CRP remained unchanged after treatment. In patients with psoriatic arthritis, the median pretreatment YKL-40 was 112 μg/L and 43% had elevated YKL-40. YKL-40 decreased in 33 patients who responded to adalimumab (from 112 μg/L to 68 at 48 weeks, P = 0.007). Hs-CRP decreased (from 4.65 mg/L to 0.91, P = 0.013) in the responders. In the non-responders (n = 9), YKL-40 and hs-CRP remained unchanged.
  
  
  CONCLUSIONS
  YKL-40 is elevated in many patients with psoriatic arthritis, but not in patients with psoriasis. YKL-40 decreased in patients with psoriatic arthritis who responded to treatment. YKL-40 may be a useful biomarker to monitor the effect of treatment with tumour necrosis factor-α inhibitors in patients with psoriatic arthritis.
authors.affiliation: Department of Dermato-Allergology, Copenhagen University Hospital Gentofte, Hellerup, Denmark. peter.jensen@regionh.dk
authors.forename: P
authors.initials: P
authors.lastname: Jensen
authors.forename: C
authors.initials: C
authors.lastname: Wiell
authors.forename: K
authors.initials: K
authors.lastname: Milting
authors.forename: R P
authors.initials: RP
authors.lastname: Poggenborg
authors.forename: M
authors.initials: M
authors.lastname: Østergaard
authors.forename: J S
authors.initials: JS
authors.lastname: Johansen
authors.forename: L
authors.initials: L
authors.lastname: Skov
mesh_terms: D054392:Adipokines / Q000097:blood*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015535:Arthritis, Psoriatic / Q000097:blood* / Q000175:diagnosis*; D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein / Q000032:analysis; D000071451:Chitinase-3-Like Protein 1; D005260:Female; D006801:Humans; D037102:Lectins / Q000097:blood*; D008297:Male; D008875:Middle Aged; D011565:Psoriasis / Q000097:blood; D055815:Young Adult
chemical_list: D054392:Adipokines; D015415:Biomarkers; C084533:CHI3L1 protein, human; D000071451:Chitinase-3-Like Protein 1; D037102:Lectins; D002097:C-Reactive Protein