The absence of back pain in classical ankylosing spondylitis.

Despite the early description of painless spinal ankylosis, the existence of a clinical subset of ankylosing spondylitis with silent axial disease has largely been overlooked. Of 45 patients who met Rome diagnostic criteria for ankylosing spondylitis, five denied ever having back pain either as an initial symptom or during the subsequent course of their illness. All had decreased lumbar spine motion and bilateral radiographic sacroiliitis of at least grade III severity. Chest expansion was decreased in four, and radiographic involvement of the cervical and lumbar spine was observed in three and two patients, respectively. There were no differences observed in sex or race distribution, or frequencies of peripheral arthritis, heel pain, acute uveitis, genito-urinary infection or HLA-B27 positivity when these patients were compared with the remaining patients with back pain. These patients support the existence of a "latent" form of ankylosing spondylitis with silent axial disease.