Zoledronic acid does not reduce MRI erosive progression in PsA but may suppress bone oedema: the Zoledronic Acid in Psoriatic Arthritis (ZAPA) Study.

BACKGROUND: The effect of zoledronic acid (ZA) on articular bone in patients with psoriatic arthritis (PsA) was investigated using MRI.

METHODS: Patients with erosive PsA were randomised to receive 3-monthly infusions of ZA or placebo for 1 year. An additional 'tests alone' group received no infusions. Clinical assessments and MRI scans were performed at baseline and 1 year.

RESULTS: Paired 1.5T MRI scans were available in 22 patients including 6 who received ZA and 16 who did not (non-ZA = 6 placebo + 10 'tests alone' patients). The Disease Activity Score (28 swollen and tender joints, C reactive protein fell over 12 months to a greater degree in patients on ZA than in non-ZA patients (-1.6 vs -0.3, p=0.023). The MRI bone oedema score decreased in the ZA group (15.5 to 8.5) but increased in the non-ZA group (14.0 to 18.0) (p= 0.0056) with regression of bone oedema at 13.5% of sites in ZA patients vs 1.3% in non-ZA patients (p = 0.0073) and progression in 1.3% of sites in ZA patients vs 6.9% in non-ZA patients (p = 0.072). There was no difference between groups in change in MRI erosion score.

CONCLUSIONS: In this pilot study ZA reduced the progression of MRI bone oedema, indicating probable suppression of osteitis concordant with reduction in clinical measures of disease activity.