Background Hand bone loss is an early feature in both RA and PsA, but there is less data available on periarticular bone gain, in particular in PsA following treatment. Digital X-ray radiogrammetry (DXR) is a sensitive method for quantifying changes in periarticular bone mineral density (DXR-BMD) in the early phase of the disease.

Objectives The aim of this study was to (1) investigate DXR-BMD changes in early PsA and RA prior to and 3, 12 months after introducing an anti-rheumatic drug; and (2) to explore associations between disease-related variables and DXR-BMD.

Methods Recent-onset (<12 months), active, treatment naïve PsA and RA patients were selected. Hand BMD was measured by DXR based on digitized hand radiographs (Sectra, Sweden) at baseline, 3 and 12 months. Mean DXR-BMD (mg/cm²) values of both hands and changes in DXR-BMD (mg/cm²/month) were calculated and compared between the two groups at all time points. Changes in hand BMD were further analysed by dividing PsA and RA into 3 subgroups based on cut-offs for the categories normal, elevated BMD loss (>-0.25 mg/cm²/month) and highly elevated BMD loss (>-2.5 mg/cm²/month). DXR-BMD was correlated with clinical parameters including ESR, CRP, DAS28-CRP4v and HAQ.

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. There were no patients taking anti-resorptive medications, 17.2% were on oral glucocorticoids (15.6% RA; 18.7% PsA) less than 10 mg per day. At 12 months 94.8% of the patients were on a DMARD and 34.5% on a TNF inhibitor (33.3% RA; 35.7% PsA).

Mean DXR-BMD decreased in both diseases at 3 months and was significantly lower in RA at 12 months (p=0.004) compared to baseline. In contrast mean DXR-BMD increased in PsA over 12 months (p=0.07) and was higher at both 3 and 12 months compared to RA.

DXR-BMD loss were significantly higher in RA compared to PsA from baseline to 12 months (p=0.0005) and also from 3 to 12 months (p=0.0006). There were no bone loss in 91.7% of patients with PsA, but only in 40.7% of patients with RA between baseline and 12 months. Among all patients with elevated BMD loss, change in DXR-BMD was less marked in the PsA group compared to RA from baseline to 3 (p=0.018) and from 3 to 12 months (p=0.014). Highly elevated bone loss was present only in the RA cohort (7.5%) at 12 months.

Disease activity scores were significantly lower in PsA than in RA at baseline and 3 months. ESR, CRP, DAS28-CRP4v improved significantly in both diseases during the study. Mean DXR-BMD correlated negatively with ESR at 12 months in RA (r = -0.39; p= 0.038), however no other significant correlations between other clinical parameters and DXR-BMD were found.

Conclusions To our knowledge this is the first prospective study showing hand bone loss as early as 3 months measured by DXR in both PsA and RA despite intervention of appropriate anti-rheumatic drug. After 1 year of treatment we observed cortical bone gain in PsA but further bone loss in RA supporting the hypothesis of different pathomechanisms being involved in hand bone remodelling in PsA.

Disclosure of Interest A. Szentpetery: None Declared, M. Haroon: None Declared, P. Gallagher: None Declared, E. Heffernan: None Declared, O. FitzGerald Grant/research support from: Abbott, BMS, Pfizer, MSD, Consultant for: Abbott, UCB, Pfizer, Speakers bureau: Abbott, Pfizer, MSD