Isolated sacroiliitis as monosymptomatic form of ankylosing spondylitis--a possible cause of chronic back pain.

In a retrospective analysis of 770 cases of ankylosing spondylitis or allied disorders 146 patients (19 percent) were found to have isolated sacroiliitis without involvement of the spine. The mean disease duration of isolated sacroiliitis was 11.9 years. The conclusions were based on anamnestic, clinical and radiological data. Of those patients with isolated sacroiliitis 29 percent were female, compared to 11 percent of female patients with typical spinal disease. Cases restricted to the sacroiliac joints for a longer period can be observed frequently in younger patients and may be regarded as an abortive and monosymptomatic form of ankylosing spondylitis insofar as other seronegative spondarthritides can be excluded.