Ankylosing Spondylitis (AS) is a chronic painful progressive inflammatory arthritis of unknown etiology primarily affecting the spine and sacroiliac joints. In addition to formation of new bone leading to syndesmophytes and ankylosis; osteoporosis is also a prominent feature in AS-thus showing the paradox of new bone formation at abnormal sites coexisting with reduced bone mass & increased fracture risk. Osteoporosis is a common complication of AS, with an incidence between 18.7% and 62%. TNF alpha has a central role in disturbing this balance in bone metabolism--resulting in accelerated alveolar bone loss and decreased strength- i.e. osteoporosis. The investigators hypothesis that anti TNF therapy is effective in active AS resistant to conventional therapy and helps in improving the bone density and over all bone health.

Ankylosing spondylitis not responding to conventional therapy has been effectively treated with Anti TNF therapy. In addition studies have shown that TNF has a role in osteoporosis of inflammatory diseases. The hypothesis that anti TNF therapy may decrease osteoporosis and tilt bone metabolism to the osteoblastic side has been tested in few studies. These have not been studied in an Indian population. Another great issue in the usage of anti TNF therapy in Indian population is the high incidence of developing infective complications; especially tuberculosis. The investigators are thus studying these in a north Indian population at a tertiary centre. The results would come to important conclusions regarding treatment and in the important issue of tuberculosis screening and prevention.

Inclusion Criteria:

• Patients who are fulfilling the Modified New York Criteria(1984) for the diagnosis of Ankylosing Spondylitis
• Age ≥ 18 years
• Patients who have been planned to be started on anti Tnf alpha agents.
• Patients who have given consent for the study.

Exclusion Criteria:

• Patients with other coexistent rheumatologic diseases.
• Patients who have previously received anti TNF alpha agents in the past 1 year.
• Patients who are receiving other medications that may significantly alter the bone metabolism (like steroids, bisphosphonates, estrogen replacement therapy etc)
• Patients with any contraindications against the usage of anti TNF alpha agents (Active/ chronic infections, liver dysfunction, demyelinating diseases, pregnancy etc)
• Patients with other definite risk factors for osteoporosis like chronic alcoholism, smoking, endocrine disorders etc