Objectives Objective of this study was to present characteristics of Ankylosing spondilitis (AS), not initiated as genuine (i.e. initiating as a reactive arthritis-ReA).

Methods The study is a retrospective 20-year analysis of 144 patients treated for ReA.

Results

1. Spondylitis occurred after either urinary or intestinal infection in 87%; in 53%- following mono- or oligoarthritis.

2. Syndesmophytes of one or more segments were massive, nonmarginal; sacroiliitis-asymmetrical.

3. After the period of 10,6 years, in 25% of diseased, the total spinal column was involved by AS type, with symmetrical sacroiliitis.

4. Some discs presented with calcification resulting from discitis.

5. Some i.v. spaces were reduced including some vertebral bodies which underwent a cuneiform transformation.

6. Postural transformation was less frequent, lumbar lordosis was recorded in 83% with lower frequency of TH kyphosis than in AS.

7. There were cases of interspinal arthrosis and other secondary degenerative transformations.

8. Neurological and/or motorial deficit was recorded in 85% (damage of sensibility, tendon reflexes or motoricity).

9. Function of the spinal column was preserved for the period of 10,5 years on average if the process was of segment character, which referred also to the respiratory function in which the abdominal type of breathing was predominant after 15,5 years.

Conclusion The presented differences occur for slow process of development of Sp in ReA, because of the involvement of either one or a small number of vertebral units of the spinal column and the presence of discitis, whereas in AS, the course of ossification of the fibres of annulus fibrosus is faster than the destruction of the discus, inner fibres of annulus fibrosus and nucleus pulposus being preserved, in this way the i.v. spaces remain unreduced, not allowing neither discovertebral conflict nor the resulting neurological damage.