It will be a pilot, 2 year, prospective, randomized, double-blind, placebo-controlled (for pamidronate) study. All patients with AS will receive treatment with TNF inhibitor, while randomization will be performed for pamidronate versus placebo group. Primary outcome will be the rate of radiographic progression of AS, calculated after 24 months of combined treatment.

It will be a pilot, 2 year, prospective, randomized, double-blind, placebo-controlled (for pamidronate) study. All patients with AS will receive treatment with tumor necrosis factor (TNF) inhibitor, as indicated by local guidelines. Randomization will be performed for pamidronate vs placebo group. Pamidronate will be prescribed as monthly intravenous infusion in the dose of 60 mg/month for the first 6 consecutive months of every study year. Primary outcome will be the rate of radiographic progression of ankylosing spondylitis (AS), calculated after 24 months of combined treatment. Clinical and laboratory disease parameters will serve as secondary outcomes. These outcomes as well as safety assessments will be performed on a monthly basis up to 24 months.

Inclusion Criteria:

• presence of spinal syndesmophytes
• normal renal and liver function
• eligibility to receive anti-TNF treatment according to local guidelines

Exclusion Criteria:

• unwilling to sigh the informed consent
• presence of significant systemic or organ-limited disorders, other than AS
• any contraindication for anti-TNF or pamidronate treatment
• presence of acute dental/periodontal disease