Enthesitis in Ankylosing Spondylitis

General Comments

Ankylosing Spondylitis is associated with enthesitis at multiple sites. It is the commonest inflammatory polyenthesitis of the spine.

It has a predisposition to involve entheses of the spine from the low back where it most typically starts. It also involves the lumbar, thoracic and cervical spine. After the spine it most typically involves entheses of the hip or shoulder joints.

The biomechanics, functioning and tissue architecture of the sacroiliac joint in the low back is virtually identical to an insertion site. Early Ankylosing Spondylitis most typically is recognised due to sacroiliac joint inflammation.

Ankylosing spondylitis can also manifest as peripheral enthesitis such as Achilles tendonitis or plantar fasciitis or other isolated enthesopathies. A young person may present with inflammatory symptoms at these sites years before a diagnosis is established.

Patients may occasionally develop swollen joints. When these are scanned there may be evidence of internal enthesitis.

Types of enthesitis in Ankylosing Spondylitis

The skeleton is held together by a massive network of entheses starting at the base of the skull and ending at the nails of the hands and feet (See Nails and Enthesopathy). Therefore, entheseal pain related to Ankylosing Spondylitis can be manifest at many sites and may be misdiagnosed as other entities. These include:

  • Heart attacks- young patients with enthesitis may even have had an angiogram
  • Pulmonary embolism
  • Pleurisy
  • Shoulder tendonitis
  • Bursitis
  • Sciatica - may lead to inappropriate surgery
  • Disc Disease - may lead to inappropriate surgery

Ankylosing Spondylitis can also present with an acute painful red eye with blurred vision. There is evidence linking this eye inflammation to micro-machine enthesitis in the small muscles that move the eye lens and iris

Occasionally Ankylosing Spondylitis can affect the root of the major blood vessel called the aorta at the point where it is inserted into the heart. This is an insertion point but is structurally different to those in the skeleton. Fortunately this complication of aortic root inflammation is rare.

Knowledge of enthesis relevant to the diagnosis of Ankylosing Spondylitis

The majority of the entheses commonly involved in Ankylosing Spondylitis are located too deep to visualise or to directly examine.

The diagnosis of Ankylosing Spondylitis may not be suspected if the patient presents to the physician with peripheral enthesitis.

Inflamed entheses may not be obviously swollen due to the enthesis micro-anatomy or its special structure.

The physician may fail to differentiate between inflammatory and mechanically induced enthesopathy.

X-rays and blood tests may be normal.

Even when the correct type of Magnetic Resonance Imaging scan is performed it can occasionally be normal.

Consequently the patient could be wrongly told that they do not suffer from enthesitis related diseases like Ankylosing Spondylitis.

These factors can contribute to the diagnosis being delayed for years or in some cases completely missed.

What patients with possible enthesitis related to Ankylosing Spondylitis should check for

a) Things to check for in person or family members

There may be a family history of Anklyosing Spondylitis and it is commoner in first degree relatives.

There may be a family history of psoriasis or a personal history of psoriasis including nail disease.

There may be a family history of bowl inflammation or colitis.

There may be a history of painful inflamed eyes or uveitis.

b) Symptom check

The hallmark of enthesitis that is inflammatory in nature is early morning stiffness that improves with activity.

However, the pain may persist throughout the day with severe enthesitis.

Inflammation in the low back is associated with pain that radiates into the buttocks.

The pain "flip-flops" from buttock to buttock.

The pain may go down the leg but usually not below the knee.

It may respond to anti-inflammatory drugs.