Chest wall complications from AS

Ankylosing spondylitis is a chronic inflammatory disease affecting joints of the axial skeleton with resultant fibrosis and ossification of the ligamentous structures of the spine, sacroiliac joints, and rib cage [1]. Patients present most frequently with chronic low back pain, and clinical findings often include limited spinal range of motion, bilateral sacroiliitis on plain radiographs, and positive serology for HLA-B27 in 90 to 95 percent of patients. Individuals may rarely complain of exercise intolerance. Extraarticular manifestations of the illness include ocular disease (anterior uveitis, 25 percent) and cardiovascular disease (including aortitis, aortic insufficiency, aortic root dilation, thoracic aortic aneurysms, conduction abnormalities), and peripheral arthritis occurs in 10 to 20 percent of patients [2].

Ankylosing spondylitis causes pleuropulmonary disease in less than 2% of patients, most commonly in the form of chest wall restriction and upper lobe fibrocystic parenchymal disease. Less commonly, ankylosing spondylitis affects the cricoarytenoid joint, and patients can present with hoarseness, sore throat, upper airway obstruction, or respiratory failure. In addition, these patients are at increased risk for spinal cord injury when undergoing endotracheal intubation.

Pathophysiology

Ankylosing spondylitis causes fixation of the chest wall through fusion of the costovertebral joints from inflammation [4-6]. Similarly, the anterior chest wall can be affected by enthesitis (inflammation of the muscular or tendinous attachments to bone) of the manubriosternal symphysis and sternoclavicular joints. Clinical evidence of chest wall disease includes limitation of chest wall expansion to 2.5 centimeters when measured at the level of the fourth intercostal space [7].

Pulmonary function

Despite chest wall restriction, patients will often manifest only a mild restrictive ventilatory defect, with a mild decrease in the total lung capacity (TLC) and vital capacity (VC) [4]. Relative preservation of lung volumes has been attributed to compensation by the diaphragm with increased abdominal excursion, fixation of the thorax at greater lung volumes, and preservation of chest wall symmetry and rib excursion [4-6,8]. The functional residual capacity (FRC) and residual volume (RV) are normal or increased due to fixation of the rib cage in an inspiratory position. Gas exchange, airflow, and lung compliance are usually normal. Maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) may be mildly reduced [8,9].

Exercise tolerance

Patients may rarely complain of exercise intolerance. Formal testing may reveal exercise limitation with decreased maximal oxygen consumption (VO₂max), but the extent to which this correlates with limited chest wall expansion is debated [10,11]. Some authors report that exercise limitation does not occur until the vital capacity (VC) is less than 75 percent predicted [12], while others have invoked additional factors such as deconditioning and inspiratory muscle fatigue to account for the exercise limitation [13]. Non-specific body fatigue can confound interpretation of self-reported exercise capacity capability [14].

Treatment

Treatment is primarily preventive and supportive. There is debate about whether disease activity, as assessed by the erythrocyte sedimentation rate (ESR), correlates with the decline in VC [5,15]. Anti-inflammatory therapy has not been shown to influence the pulmonary disease or the underlying illness. Spinal extension exercises may be beneficial in maintaining mobility [6]. A number of preliminary reports on the use of TNF blockers in ankylosing spondylitis suggest short-term improvement in disease activity ratings and quality of life measures [16-18]. Changes in pulmonary function tests and respiratory symptoms have not been assessed consistently.

Parenchymal disease

Apical fibrobullous disease develops in approximately 1 percent of patients, with a male to female predominance of 50:1 [2,19]. Affected patients have usually suffered from ankylosing spondylitis for at least 15 years. Possible etiologies of this complication include:

• Inflammatory lung disease
• Repeated aspiration from associated esophageal muscle dysfunction (with diminished clearance of secretions due to chest wall disease)
• Decreased ventilation of, or altered apical stresses to, the upper lung fields as a result of chest wall disease.

The course of the fibrosis may be progressive, and no therapy of uncomplicated apical fibrosis has been shown to alter the direction of the illness [4,19]. This condition is usually clinically silent until superinfection occurs, most commonly with Aspergillus or mycobacterial species [2]. Because of the location of pulmonary disease and its radiographic appearance, tuberculosis must be excluded. These patients are also at increased risk for spontaneous pneumothorax.