Ankylosing Spondylitis

Abstract

Ankylosing spondylitis (AS) is a chronic inflammatory arthritis characterized by sacroiliitis, enthesitis, and a marked propensity for sacroiliac joint and spinal fusion. This arthritis is part of the spondyloarthritis family of diseases, which have similar clinical, genetic, and immunologic features. The goals of treatment of AS are to reduce symptoms, maintain spinal flexibility and normal posture, reduce functional limitations, maintain work ability, and decrease disease complications.

Keywords

Ankylosing, Exercise, HLA-B27, Physical Therapy, Physical Therapy (specialty), Sacroiliitis, Spondylitis, Spondyloarthropathies

Synonyms
Seronegative spondyloarthropathy Seronegative arthritis Seronegative spondyloarthritides HLA-B27 associated spondyloarthropathy
ICD-10 Codes
M45.0	Ankylosing spondylitis of multiple sites in spine
M45.1	Ankylosing spondylitis of occipito-atlanto-axial region
M45.2	Ankylosing spondylitis of cervical region
M45.3	Ankylosing spondylitis of cervicothoracic region
M45.4	Ankylosing spondylitis of thoracic region
M45.5	Ankylosing spondylitis of thoracolumbar region
M45.6	Ankylosing spondylitis of lumbar region
M45.7	Ankylosing spondylitis of lumbosacral region
M45.8	Ankylosing spondylitis of sacral and sacrococcygeal region
M45.9	Ankylosing spondylitis of unspecified sites in spine

Definition

Ankylosing spondylitis (AS) is a chronic inflammatory arthritis characterized by sacroiliitis, enthesitis (inflammation of the soft tissues attaching tendons, ligaments, and joint capsules to bone), and a marked propensity for sacroiliac joint (SJ) and spinal fusion. This arthritis is part of the spondyloarthritis (SpA) family of diseases, which have similar clinical, genetic, and immunologic features; however, AS has universal involvement with SJ inflammation or fusion, and more prevalent spinal ankylosis. Peripheral involvement is less common in AS, but paravertebral ligaments and attachments of the Achilles tendon and plantar fascia are occasionally affected. Peripheral joints can also be involved in the more severe forms of the disease or when the patient has a younger age of onset. The onset of symptoms of AS is usually in late adolescence or early adulthood, and there is a 3:1 male predilection. AS is not associated with the presence of rheumatoid factor, anticyclic citrullinated peptide antibody, or antinuclear antibodies (ANA), although there is a genetic association with the HLA-B27 histocompatibility antigen. Approximately 90% of AS patients express the HLA-B27 genotype; however, this marker is not useful for screening, as only 5% of individuals with the HLA-B27 genotype develop AS.

There are various classification criteria for AS, including the Modified New York Criteria for AS, the European Spondyloarthritis Study Group criteria for SpA, and the Amor criteria for SpA that have a role in epidemiologic studies, therapeutic trials, and other forms of clinical research. These classification criteria mainly rely on radiographic features; however, these may take years to develop and therefore potentially exclude patients with early manifestations. Consequently, the Assessment in Ankylosing Spondylitis (ASAS) classification of SpA included the term “nonradiographic axial SpA,” which gave magnetic resonance imaging (MRI) a significant role in the classification and diagnosis of AS and SpA.

Symptoms

Inflammatory spondyloarthropathies should be suspected in any young adult patient who complains of insidious onset, progressively worsening, dull, thoracolumbar or lumbosacral back pain. Other characteristics that should raise suspicion for inflammatory-mediated axial disease include: back pain that improves with exercise, no improvement with rest, beneficial response to nonsteroidal anti-inflammatory medications, and pain during the night.

AS can have a variable presentation, but sacroiliac pain is a common complaint accompanied by progressive morning stiffness and prolonged stiffness after inactivity. Tendon and ligament attachment sites may become painful and swollen, and one third of patients may develop hip or shoulder pain. Pleuritic chest pain and inflammatory eye disease (uveitis) tend to be late symptoms of more severe disease. Neurologic symptoms, such as paresthesia and motor weakness, are usually absent.

Physical Examination

In addition to a complete physical exam, the evaluation of a patient with AS should focus on three regions: entheses, peripheral joints, and axial joints. The most typical findings on physical examination include signs of decreased spine mobility, sacroiliac pain, and pain at sites of ligament and tendon attachments. On palpation, the spine, lower paraspinal muscles, and SJs may be tender. Palpation of extremities demonstrates pain at entheses sites, particularly around the heel (e.g., calcaneal enthesitis) and knee (i.e., tibial tuberosity). The Gaenslen test may be positive ( Fig. 121.1 ), and a Flexion Abduction External Rotation or Patrick test might also be abnormal, suggesting SI joint pathology.

Peripheral joint swelling and pain with decreased range of motion (ROM) can be seen in 25% to 30% of patients. A discolored and edematous iris with circumferential corneal congestion occurs in iritis and anterior uveitis. The neurologic evaluation is typically normal with regard to motor, sensory, and reflex examination findings. Weakness may be noted, but it is usually associated with pain, loss of mobility, or disuse. Tests of spinal mobility including the modified Schober test, finger to floor distance, cervical rotation, occiput or tragus to wall distance, and chest expansion should be performed on every visit. The modified Schober test is performed with the patient initially standing in erect position. The examiner identifies the posterosuperior iliac crest line (i.e., lumbosacral junction) and makes two midline marks, one 10 cm above the iliac crest line and one 5 cm below the iliac crest line. The patient is then instructed to perform forward trunk flexion while the examiner measures the distance between the two marks ( Fig. 121.2A–C ). Normal spinal mobility is indicated by an increase of more than 5 cm or a total distance greater than 20 cm, whereby an increase less than this would suggest limited lumbar spine mobility. The inability to touch the occiput to the wall while standing against it and the inability to expand the chest by more than 3 cm in full inhalation are late findings in the disease.

Functional Limitations

The functional limitations of the patient with AS are typically related to spine pain and immobility. The three best predictors of decreased spinal mobility are cervical rotation, modified Schober test, and finger to floor distance, although these measurements have not correlated with patients’ assessment of disease activity. Early in the disease process, decreased spine ROM is secondary to back pain and muscle spasms, and most dysfunction is mild and self-limited, typically improving with treatment. In severe disease, limitations from hip flexion contractures, thoracic kyphosis, and loss of cervical rotation decrease patients’ ability to view activities in front of them and side to side. The most commonly reported activity limitations are interrupted sleeping, turning the head while driving, carrying groceries, and having energy for social activities. Limitations in chest wall motion lead to a reliance on diaphragmatic breathing and a secondary drop in aerobic capacity. Pain, posture, and functional impairments can also significantly impact sexual relationships.

The Bath Ankylosing Spondylitis Functional Index and the Dougados Functional Index are functional assessment tools used by clinicians specializing in the care of patients with AS to measure daily function. Past studies have shown approximately 90% of patients with AS remain employed, although evidence suggests up to one third of patients experience some form of employment disruption due to pain and physical limitations.

Diagnostic Studies

There is a well-documented lag time between initial onset of symptoms and diagnosis that ranges from 7 to 11 years. Given the lack of specific signs and symptoms for early AS, a high level of suspicion is required in young patients presenting with back pain. Laboratory investigation should include inflammatory markers: erythrocyte sedimentation rate and C-reactive protein. Approximately 40% of patients with AS will have normal inflammatory markers, but the elevation of acute phase reactants can indicate severity, responsiveness to treatment, peripheral joint involvement, or extra-articular disease. HLA-B27 is present in 90% of patients with AS, and the absence of this histocompatibility complex genotype suggests milder disease with a better prognosis. Rheumatoid factor and ANA are usually absent.

Spine and pelvis radiographs are the standard imaging modalities in diagnosis and assessment of disease, although computed tomography (CT) and MRI are more sensitive for detecting bony changes, especially early in the disease course. Spine radiographs show ossification of spinal ligaments and apophyseal joints, sclerosis, and syndesmophytes, with eventual ankylosis that leads to the classic bamboo spine appearance ( Fig. 121.3 ). Pelvic (sacroiliac + hip) radiographs demonstrate symmetric involvement of the SJs with bone erosions, sclerosis, and blurring of the subchondral bone plate, eventually progressing to complete ankylosis. Based on modified New York Criteria for AS, radiographic features of moderate bilateral sacroiliitis or moderate to severe unilateral sacroiliitis plus one clinical feature are required for definite diagnosis of AS. Additional radiographic findings include bone erosions at entheses, symmetric and concentric joint narrowing, and subchondral sclerosis of the hip joints with ankylosis in severe disease. Once initial radiographs are abnormal, further radiographic progression correlates with worsening results of the modified Schober test, although it is recommended that assessment of spinal mobility be used as a proxy for radiographic evaluation.