Ankylosing Spondylitis

Ankylosing arthritis (AS) is also known as Bechtrew disease is a type of inflammatory arthritis. Ankylosing spondylitis mostly involves the spine but may involve other peripheral joints as well. The management of ankylosing spondylitis has vastly improved with newer medication that halts the progression of the disease. Most patients benefit from medical therapy and only a few patients may require surgery for correction of the deformity.

Syndesmophytes in Ankylosing Spondylitis

Affected Population

Younger patients in the age groups of 15-45 years are affected and males are more frequently affected than females. The disease may run in the family with a genetic marker of HLA B27, but not all HLA B27 patients have ankylosing spondylitis. Although, the majority of patients with ankylosing spondylitis have HLA B27 present.

Causes & Pathogenesis

The exact cause of ankylosing spondylitis is unknown but various genetic and autoimmune pathways play a role in its pathogenesis. The cells of the body that function to protect the body against foreign particles/cells such as infection start to malfunction. These immune cells recognize certain parts of the body as foreign and attack these structures. The primary target of these cells in ankylosing spondylitis is bone/cartilage interface, especially at the site of insertion of tendon/ligaments in the bone (enthesis).

The inflammation of the enthesis leads to the destruction and erosion of the bone and the surrounding soft tissues. The autoimmune destruction eventually leads to ossification of the soft tissue structures and bony fusion of the involved joint. In ankylosing spondylitis, the joint where the lower spine meets with the pelvic bone (sacroiliac joint) is most commonly involved.

The repair process that follows the destruction of the enthesis in ankylosing spondylitis leads to bone formation (ossification) in the soft tissues. There is inflammation of the outer ring of the intervertebral disc and subsequent fusion of the involved vertebrae through osteophytes (syndesmophytes).

Symptoms

There is typically a low back pain that improves with activity and gets worse with rest. The patients complain of morning stiffness in the back that lasts more than 30 minutes. Occasionally the patients may wake up at night secondary to pain.

There may be systemic manifestations of the ankylosing spondylitis in the form of inflammation of the eyes and amyloid deposition disease of the lungs or kidney, etc.

Besides the spine, other peripheral joints may be involved in ankylosing spondylitis. The large joints in the lower extremities such as hip joints may be more commonly involved than shoulder joints. Like the sacroiliac joint, other sites of enthesis may be involved such as the Achilles tendon in the ankle, plantar fascia in the feet, and pubic symphysis in the pelvis.

Spine Deformity

Spinal deformity is one of the leading causes of morbidity and mortality in ankylosing spondylitis. The patient may form a hunched back deformity of the spine (kyphotic deformity). In the initial stages, the patient tries to compensate for the hunched back deformity by bending their knees and extending their hips while standing/walking. In the advanced stages when the hips also get involved, the patient’s spine deformity becomes more apparent.

To compensate for the loss of the forward vision from the hunched back, the patient tries to extend the neck. As the disease progresses the ability to extend the neck is limited and leads to the characteristic ‘chin in the chest’ position. The patient then tries to compensate by rolling his/her eyes upward to look forward.

The kyphotic deformity continues until the rib cage bends forward to meet the bony pelvis in the front. This may compress the abdominal organs and interfere with their function. The patient is unable to inflate and deflate their lungs fully during breathing leading to difficulty breathing. The ankylosed (fused) spine becomes vulnerable to fractures with minimum trauma. Extension fractures may occur in the cervical spine followed by the thoracic spine.

Diagnosis

The diagnosis of ankylosing spondylitis is made by the orthopedic surgeon after extracting a thorough history and conducting a detailed physical examination. The surgeon may measure the chest expansion and the flexibility of the lower spine upon bending forward.

Blood investigations form an important part in the diagnosis of ankylosing spondylitis. The physician may subject the blood to look for markers of inflammation such as ESR, CRP, anti-CCP, and HLA B27 to look for genetic association. Radiological investigations in the form of X-rays are done in special views to look for erosion and ossification. The physician may also request a CT scan or an MRI for a more detailed evaluation. While CT scan is very sensitive to bony abnormalities, an MRI is the best modality for the detection of AS in young patients.

Classification

Modified New York criteria are used to diagnose ankylosing spondylitis. Ankylosing spondylitis is diagnosed if the radiological criteria is met with at least one clinical criteria. The radiological criteria consist of grade 2 or more sacroiliitis (inflammation of SI joint) on both the SI joints on plain X-ray or grade 3 or 4 sacroiliitis on one of the SI joints.

The clinical criteria consist of:

• Low back pain and stiffness persisting for more than 3 months which improves with exercise but not rest, or
• Limitation of movement in the lumbar spine in both front to back and side to side motion planes, or
• Limitation of chest expansion

Management

Medical therapy is the mainstream treatment after the initial diagnosis of ankylosing spondylitis. Nonsteroidal anti inflammatory medications are the first choice medications and are given continuously. The medications are carefully balanced in the view of gastritis and bleeding diathesis.

Disease modifying anti rheumatic drugs (DMARDS) such as sulfasalazine and methotrexate may be used when the NSAIDs fail to act. Corticosteroids and TNF alpha inhibitor medications may be used as well. The medications are given keeping in mind their interactions and side effects.

The surgical management in ankylosing spondylitis is reserved for patients in whom the disease causes strong limitation of daily life. The surgical management is also done for patients with neurological symptoms, progressive deformity, chronic pain, and fractures.

The type of surgery depends upon the indication for the surgery. Bone cutting surgery or osteotomies together with lumbar fusion surgery may be done to correct the deformity and restore the balance of the spine.