Thorax in ankylosing spondylitis.

Rigidity of the thorax in ankylosing spondylitis was first recognized as long ago as 1695, when Bernard Connor described a skeleton showing the characteristic rigidity of the thoracic cage and lumbar spine and concluded that respiration must have been greatly restricted during the life of the unfortunate sufferer. This astute observation remained the only one of its kind until Hilton Fagge (1877) reported on the ankylosis of the ribs with the vertebrae. However, it is only since 1945 that close attention has been paid to the effect of ankylosing spondylitis on the respiratory system. Involvement of the thorax is one of the essential features which differentiate ankylosing spondylitis from rheumatoid arthritis. For many years the former condition was considered, largely because of histological similarities, to be a form of rheumatoid arthritis, but there is now wide agreement (13th Rheumatism Review, Smyth and 12 others, 1960) that the two conditions should be clearly distinguished and regarded as separate clinical entities. The manner in which the thoracic rigidity occurs is well known. Pathological changes occur in any of the articulations of the thorax, progressing to bony ankylosis. The articulations most commonly affected are those between ribs and vertebrae, ankylosis occurring at both the costo-transverse and costo-vertebral joints. In addition to the changes in the spinal column, involvement of the sterno-manubrial and sterno-clavicular joints also contributes to the rigidity of the thorax. In cases where there is severe kyphosis there is gross deformity as well as rigidity of the thorax. As the disease progresses the respiratory movements become more and more restricted until respiration is almost entirely diaphragmatic. Opinion is divided over the position which the ribs take up when ankylosis occurs, some authors finding this to be in inspiration (Travis, Cook, Julian, Crump, Helliesen, Robin, Bayles, and Burwell, 1960; Zorab, 1960), others in expiration (12th Rheumatism Review, 1959; Rogan, Needham, and MacDonald, 1955). This paper is based on a clinical experience of 360 patients suffering from ankylosing spondylitis who have been referred to Westminster Hospital since 1945. Pulmonary function tests have been performed on 22 patients, none of whom was especially selected on account of thoracic involvement. Clinically these patients showed all degrees of severity of the disease. Studies were also made on normal subjects, in whom thoracic stiffness was simulated by the application of a tight corset.