Background There is a growing interest in bone and cartilage biomarkers that could be used predicting and assessing changes in structural damage in inflammatory arthritis. Disease-related bone loss assessed by dual-energy X-ray absorptiometry (DXA) is a well known feature in RA and PsA, however data on bone loss during the first year of treatment in early disease are limited.
Objectives (1) To study changes in serum levels of bone biomarkers and bone mineral density (BMD) measurements in early PsA and RA prior to and 12 months after introducing an anti-rheumatic drug; (2) To explore associations between disease-related variables, serum bone biomarkers and BMD measurements; (3) To investigate if serum bone biomarkers prior to treatment predict systemic bone loss over 1 year in patients with PsA and RA.
Methods Recent-onset (<12 months), active, treatment naive PsA and RA patients were recruited. We measured serum bone-specific alkaline phosphatase (bone ALP), a marker of bone formation, and C-terminal cross-linking telopeptide (CTX-I), a degradation marker of type-I collagen reflecting systemic bone resorption at baseline, 3 and 12 months by immunoassay. We assessed bone remodelling balance by calculating bone ALP/CTX-1 ratios. BMD measurements were obtained at left total hip and lumbar spine at baseline and 12 month by DXA. Clinical parameters were correlated with bone biomarkers and BMD measurements.
Results 64 patients (32 PsA, 32 RA) were included with median age 43 years. 95% of the patients were commenced on a DMARD therapy at baseline and 11.7 % (12.5% RA; 10.7% PsA) were also started on a TNF inhibitor. At 12 months 94.8% of the patients were on a DMARD and 34.5% on TNF inhibitor (33.3 % RA; 35.7% PsA).
Bone ALP levels did not change significantly in either cohort during the study. CTX-I levels decreased after 3 months of treatment in RA (p=0.013) and in the entire group (p=0.043) remaining lower at 12 months (p= 0.042; p= 0.012 respectively) compared to baseline. Bone ALP/ CTX-I ratio was higher (p=0.05) at 1 year compared to baseline in the entire group reflecting improvement in bone remodelling balance.
Hip BMD decreased in both diseases, significantly in RA (p=0.021), whilst spine BMD decreased in RA (p=0.056) but increased in PsA (p=0.017).
CTX-I levels were correlated inversely with hip BMD in PsA at both baseline and 12 months (r = -0.38, p= 0.04; r = -0.51, p= 0.007) and similarly in the entire group (r = -0.29, p= 0.03; r = -0.3, p= 0.02). Baseline CTX-I levels correlated with the change in hip BMD over 12 month in the whole group (r = 0.31, p= 0.03).
Stepwise multiple logistic regression analysis revealed significant associations of baseline CTX-I levels with change in BMD of the hip over 12 months in PsA (OR 2.8, p=0.009) and in the entire cohort (OR 2.5, p=0.014) with the model also including bone ALP, ESR, CRP, DAS28 CRP and HAQ.
Conclusions The improvement in bone remodelling balance seen in early PsA and RA patients is most likely due to decrease in bone resorption after 1 year of appropriate anti-rheumatic therapy. High baseline levels of serum CTX-I may predict systemic bone loss at the hip over 1 year in patients with PsA.
Disclosure of Interest A. Szentpetery: None Declared, M. Kilbane: None Declared, M. O’Keane: None Declared, M. Haroon: None Declared, P. Gallagher: None Declared, S. van der Kamp: None Declared, M. McKenna: None Declared, O. FitzGerald Grant/research support from: Abbott, BMS, Pfizer, MSD, Consultant for: Abbott, UCB, Pfizer, Speakers bureau: Abbott, Pfizer, MSD
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