Ankylosing Spondylitis and Axial Spondyloarthritis

Essentials

• An integral feature of the disease is inflammation involving ligament insertion sites and facet joints of the spine as well as the sacroiliac (SI) joints.
• The condition often affects HLA-B27 positive individuals and belongs to the group of seronegative spondyloarthropathies together with
  • reactive enteroarthritis and uroarthritis Reactive Arthritis
  • enthesitis-related arthritis (ERA), a subgroup of juvenile idiopathic arthritis Juvenile Idiopathic Arthritis (Juvenile Rheumatoid Arthritis)
  • psoriatic arthritis Psoriatic Arthritis
  • arthropathy associated with inflammatory bowel disease.
• Several of the above conditions may be encountered in members of the same family, and they may all lead to ankylosing spondylitis.
• The condition is termed idiopathic when it has become chronic and no causative agent has been detected, unlike in reactive arthritis.
• Axial spondyloarthritis and ankylosing spondylitis are considered to be a continuum of the same disease, even if not all patients with axial spondyloarthritis end up having ankylosing spondylitis.

Definition and incidence

• Axial spondyloarthritis and ankylosing spondylitis are part of the same spectrum of disease; in axial spondyloarthritis inflammatory changes can be visualised at the SI joints and also at the spine by magnetic resonance imaging (MRI), but if radiographic changes are present the condition has already evolved into ankylosing spondylitis.
• Some (about one third) cases of axial spondyloarthritis will progress to ankylosing spondylitis, and these patients should receive active treatment sufficiently early.
• Ankylosing spondylitis is nearly as common as rheumatoid arthritis, but less than one third of patients are diagnosed with the clinical disease. The condition is almost as frequent in women as in men, but severe ankylosing spondylitis requiring hospital treatment is mainly encountered in men.
• The incidence peaks at around the age of 25 years, but the diagnosis is often delayed. The newer diagnosis, axial spondyloarthritis, reduces the diagnostic delay because MRI is used in the diagnostics.

Clinical picture

• It is most important that inflammatory back pain is identified, the criteria for which are fulfilled when a patient with back pain for ≥ 3 months presents with at least 4 of the following 5 criteria:
  • age at symptom onset less than 40 years
  • insidious onset of back pain
  • pain at night
  • symptoms improve with exercise
  • symptoms do not improve with rest.
• Sacroiliitis: lumbosacral and gluteal pain that wakes the patient during the second half of the night
• Stiffness after rest and sitting down
• Stiffness and pain in the spine, tender spots at the cartilages of the thorax
• Peripheral arthritis mainly affecting the large joints of the lower limbs
• Enthesitis is common in the lower limbs (pain under the heel)
• Dactylitis (sausage digit)
• Acute uveitis in 20% of patients (uveitis may be the first manifestation of the disease)
• Sometimes chronic inflammatory bowel disease (Crohn's disease or ulcerative colitis)
• Conduction defects of the heart and aortitis may occasionally occur (auscultation, ECG if in doubt)

Diagnosis Diagnosis of Low Back Pain in General Practice

• Clinical picture (see above)
• Clinical findings
  • Tenderness elicited in the SI joints by compression, palpation and manipulative stress tests (Patrick's test http://en.wikipedia.org/wiki/Patrick%27s_test)
  • Fingertip to floor distance while bending forward
  • Modified (15 cm) Schober test (normal ≥6 cm)
  • Lumbar flexion
  • Occiput to wall distance (normal 0 cm)
  • Chest expansion (the normal difference in the chest circumference between maximal expiration and maximal inspiration is ≥4-5 cm at the nipple level)
• ESR and CRP levels may be elevated.
• MRI scan of the SI joints is recommended as the primary imaging study in patients less than 35 years of age in order to detect early changes; in patients older than this, plain x-rays are suitable as the primary investigation.
• X-rays are taken of the lumbar spine (the first changes often appear at the boundary between the thoracic and lumbar spine) and the SI joints. It takes 2-8 years for radiographic sacroiliitis to evolve.
• MRI can be used to verify sacroiliitis before radiological changes are visible in plain x-rays thus allowing the assessment of the degree of the inflammation. MRI is recommended to be carried out if the clinical picture fulfils the criteria for inflammatory back pain (see above) while the x-rays of the SI joints are still normal. Oedematous changes in the spine (Romanus- and Andersson-type lesions) also support the diagnosis. Abnormal MRI findings are usually present as soon as 2 months after symptom onset. When considering the need for imaging studies it should be kept in mind that the symptom onset of ankylosing spondylitis occurs before the age of 45 years.
• HLA-B27 antigen testing in the diagnostic workup should be restricted to patients with a history that fulfils the criteria of inflammatory back pain and with symptom onset before the age of 40-45 years.
• Classification criteria for axial spondyloarthritis by ASAS (The Assessment of SpondyloArthritis international Society), see table T1.

• Osteitis condensans ilii on x-rays
• Degenerative spine diseases
• Diffuse idiopathic skeletal hyperostosis (DISH) on x-rays
• Sciatica
• Other spondylarthropathy
  • Reactive arthritis
  • Psoriatic arthropathy
  • The arthropathy associated with inflammatory bowel disease