Background Rheumatoid arthitis is an independant risk factor of a low bone mineral density (BMD). This is presumed to be a direct effect of rheumatoid inflammation on bone. The inflammatory process in Psoraitic arthitis (PsA) is thought to be different from that in Rheumatoid arthritis and involves more entheseal disease. Bone loss is also not a feature of the gross radiographic changes and indeed increased bone density is frequently quoted (Ivory digit). In the general population BMD in the hip is a better predictor of future osteoporotic fracture than BMD in the spine. It is not known whether there is any bone loss in PsA and where it occurs.
Objectives To determine whether bone loss occurs in PsA and it’s site using a nested case control approach.
Methods Patients referred to a district general hospital in the North West of England for bone mineral density assessment between June 2004 to September 2010 were studied. Patients identified as having a consultant diagnosis of Psoraitic arthritis in the database were then age and gender matched with controls who were referred and scanned with no indication for scanning. Patients with other indications for scanning other than PsA were excluded. A logistic model was then fitted to determine whether or not there was a reduction in bone density in patients with PsA compared to controls. This was performed in the spine and Hip separately. The lowest T score in either hip was used in both cases and controls. Odds ratio for the T scores were obtained in the two sites, this was adjusted for height and weight, which are apossible confounders.
Results 56 patients with Psoriatic arthritis were included in the study and were matched to 56 controls. The median age was 59.5 years in both cases and controls (IQR 53.5,68 years). 31 (56%) were female in both cohorts. Median height was 165 cm (IQR 160,175 cm) in cases and 166 cm (IQR160.5, 174.5 cm) in controls. Median weight was 72.9 kg (IQR 63.4,88.4 kg) in cases and 72.7kg (IQR 63.3,85.5kg) in controls. Median T score in the spine for cases was -1.4 (IQR -1.9,-0.6) and in controls it was -0.65 (IQR -1.75,0.44). In the lowest femoral neck the median T score was -1.2 (IQR -2.0,-0.423) and in controls it was -0.5 (IQR -1.22,0.23). The odds of having a lower bone mass density in PsA was 1.68(95% CI 1.18, 2.41) in the hip, and it was 1.03 (95% CI 0.83, 1.30) in the lumber spine. After adjustment for height and weight this relationship remained. (OR 1.69 95%CI 1.17,2.46 and 1.04 95%CI 0.84,1.31 respectively).
Conclusions Bone loss does occur in patients with Psoriatic arthitis compared to controls. This seems to occur only in the femoral neck. As the femoral neck is the most important predictor of bone loss in patients predisposed to fracture, this deserves further study. Mechanism(s) for bone loss in PsA need more research.
Disclosure of Interest None Declared