The effect of etidronate on choroidal neovascular activity in patients with pseudoxanthoma elasticum

Aim: To assess the effect of the bisphosphonate etidronate on choroidal neovascular (CNV) activity in patients with pseudoxanthoma elasticum (PXE). Methods: This is an ancillary study in a single center, randomized, double-blind placebo-controlled trial (RCT) in which 74 patients with PXE were assigned to either one-year etidronate or placebo treatment. Spectral domain optical coherence tomography (SD-OCT) imaging and color fundus photography were performed every three months for one year and were systematically assessed on signs of CNV activity. Results: In the etidronate group, 11 (30%) of the patients had CNV activity at baseline, compared to 25 (67%) of the patients in the placebo group (<i>P </i>= 0.005). The proportion of eyes with CNV activity during the study ranged from 18–33% in the etidronate group and 42-56% in the placebo group and no significant difference in improvement or worsening of CNV activity was found (<i>P</i> = 0.168). Using a generalized mixed model for repeated measures, there was a protective effect of etidronate in crude analysis (RR 0.86, 95% CI 0.75 – 0.98) that disappeared when adjusting for baseline CNV activity (RR 0.97, 95% CI 0.84 – 1.13). Conclusion: In this post-hoc RCT analysis we did not observe a protecting or deteriorating effect of etidronate on CNV activity in patients with PXE after adjustment for baseline CNV. <br>