[Value of clinical symptoms in ankylosing spondylitis]

3552 patients suffering from various rheumatic disorders were studied with respect to the significance of those clinical symptoms which are part of the internationally accepted diagnostic criteria for ankylosing spondylitis. Of these patients, 36 suffered from ankylosing spondylitis, 863 from degenerative and soft tissue disorders with pains in the lumbar spine. It could be demonstrated that these clinical symptoms are not sufficient to statistically separate the various groups of patients with satisfactory sensitivity and specificity. Furthermore, the positive predictive value of a symptom varies not only with respect to the specificity of this symptom for a disease but also to the occurrence of the disease in the population. If the disease occurs rarely a specific symptom may show a low positive predictive value whereas a less specific symptom in a common disease may have a higher positive predictive value.