Definition and incidence

Ankylosing spondylitis (AS), also known as rheumatoid spondylitis and Marie-Strumpell disease, is a chronic inflammatory disorder that primarily affects the spine and sacroiliac joints and produces fusion of the spinal vertebrae and the costovertebral joints. It is a disease of adults younger than 40 years, and it demonstrates a predilection for males (male-to-female ratio is 9:1). The disease is rare in Caucasians.

Pathophysiology

The cause of AS remains unclear. However, it is strongly associated with the histocompatibility antigen HLA-B27, the presence of which is detected in more than 90% of Caucasians with the disease.

Clinical manifestations and diagnosis

Ankylosing spondylitis is diagnosed on the basis of clinical criteria that include: (1) chronic low back pain with limitation of spinal motion (<4 cm as measured by the Schober test), (2) radiographic evidence of bilateral sacroiliitis, and (3) limitation of chest wall expansion (<2.5-cm increase in chest circumference measured at the fourth intercostal space). Extraskeletal manifestations of this disease include iritis, cardiovascular involvement (cardiac conduction defects, aortitis, and aortic insufficiency in 20% of individuals), peripheral arthritis, fever, anemia, fatigue, weight loss, and fibrocavitary (fibrobullous) disease of the apexes of the lungs. The most limiting factors associated with the disease are pain, stiffness, and fatigue.

Complications

Pulmonary complications are reported to occur in 2% to 70% of patients with AS. Apical fibrosis is the most commonly occurring abnormality followed by aspergilloma and pleural effusion with nonspecific pleuritis. In apical fibrosis, the pulmonary lesion begins with apical pleural thickening and patchy consolidation of one or both apexes and often progresses to dense bilateral fibrosis and air space enlargement. Patients with apical fibrosis usually have advanced AS. Impaired thoracic cage excursion caused by AS results in a greater impairment of apical ventilation, and this may be one factor in the pathogenesis of apical fibrosis.

The most common thoracic complication is fixation of the thoracic cage as a result of costovertebral ankylosis, which can lead to pulmonary dysfunction. In patients with this complication, motion of the thoracic cage is restricted because of fusion of the costovertebral joints; this restriction leads to a decrease in thoracic excursion. Respiratory function typically demonstrates a restrictive pattern with mild diminution of total lung capacity (TLC), vital capacity (VC), and carbon monoxide diffusing capacity (Dlco) and normal or slightly increased residual volume (RV) and functional residual capacity (FRC). Pulmonary compliance, diffusion capacity, and arterial blood gas (ABG) values usually are normal. Despite having abnormal pulmonary function, the majority of patients with AS are able to perform normal physical activities without pulmonary symptoms. It has been suggested that patients who exercise regularly and thus improve cardiovascular fitness could maintain a satisfactory work capacity.

Bone ankylosis may occur in the numerous joints around the thorax (the thoracic vertebrae and the costovertebral, costotransverse, sternoclavicular, and sternomanubrial joints), resulting in limitation of chest wall movement. Patients with AS rarely complain of respiratory symptoms or functional impairment unless they have coexisting cardiovascular or respiratory disease. Progressive kyphosis is equivalent to progressive rigidity of the thorax. Increased diaphragmatic function compensates for decreased thoracic motion, allowing lung function to be well preserved. Patients with advanced disease may have an entirely diaphragmatic respiration. Regional lung ventilation in patients with AS is normal unless they have preexisting apical fibrosis.

Cervical spondylosis affects levels C5 to C6 and C6 to C7 most often and less frequently C4 to C5, C7 to T1, and C3 to C4. The degenerative changes may result in nerve root entrapment by foraminal encroachment. The phrenic nerve, which innervates the diaphragm, is supplied primarily by the C4 nerve root and to a lesser extent by the C3 and C5 nerve roots.

Cricoarytenoid involvement may exist and can lead to respiratory dysfunction and upper airway obstruction. Cricoarytenoid dysfunction can manifest as a hoarse, weak voice. Respiratory failure from cricoarytenoid ankylosis has necessitated therapeutic tracheostomy. In all reported cases, laryngeal symptoms were present before cricoarytenoid arthritis caused airway compromise. A case of acute respiratory failure and cor pulmonale resulting from cricoarytenoid arthritis has also been reported in a patient with AS.