The effect of etanercept on osteoclast precursor frequency and enhancing bone marrow edema in patients with psoriatic arthritis

A P Anandarajah ^1*, E M Schwarz ², S Totterman ³, J Monu ¹, CY Feng ⁴, T Shao ⁴, S A Haas-Smith ⁴ and C T Ritchlin ¹

¹ University of Rochester Medical Center, United States
² Center for Musculoskeletal Research, United States
³ Virtual scopics, United States
⁴ University of Rochester, United States

^* To whom correspondence should be addressed. E-mail: allen_anandarajah{at}urmc.rochester.edu.

Accepted 13 October 2007

Abstract

Objective: The frequency of osteoclast precursors (OCPF) and the presence of bone marrow edema (BME) are potential response biomarkers in psoriatic arthritis (PsA). Previous studies suggest a central role for TNF in the formation of osteoclast precursors. To better understand this association, the effect of etanercept on OCPF and BME was analyzed in PsA patients with erosive arthritis.

Methods: Twenty PsA patients with active erosive PsA were enrolled. Etanercept was administered twice weekly for 24 weeks. OCPF was measured and clinical assessments were performed at baseline, 2, 12 and 24 weeks. Gadolinium enhanced MR images were obtained at baseline and 24 weeks.

Results: Significant improvement in joint score (p<0.001), HAQ scores (p<0.001) and SF-36 parameters, was observed after 6 months of therapy with etanercept compared to baseline. The median OCPF decreased from 24.5 to 9 (p=0.04) and 7 after 3 months and 6 months of treatment, respectively. MR images were available in 13 patients. The BME volume decreased in 47 and increased in 31 sites at 6 months. No correlation was noted between OCPF, BME and clinical parameters.

Conclusion: The rapid decline in OCPF and overall improvement in BME after anti-TNF-alpha therapy provides one mechanism to explain the anti-erosive effects of TNF blockade in PsA. Persistence of BME after etanercept treatment, despite a marked clinical response, was unexpected, and suggests ongoing subchondral inflammation or altered remodeling in PsA bone.

Keywords: MRI, bone marrow edema, etanercept, osteoclast precursors, psoriatic arthritis

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