Spondyloarthritides (ankylosing spondylitis)
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Spondyloarthritis is the 3rd main type of arthritis, after osteoarthritis and inflammatory arthritis (e.g. rheumatoid arthritis). Spondyloarthritis mainly affects the vertebral column in the form of ankylosing spondylitis, but can also be peripheral, such as in psoriatic arthritis and reactive arthritis.
In this article we will mainly be discussing the spinal (axial) manifestations of spondyloarthritis.
Spondyloarthritides (aka spondyarthritis, SpA, seronegative spondylarthropathy) are inflammatory joint diseases of the vertebral column and sacro-iliac joints, the most common of which is ankylosing spondylitis – AS.
These conditions tend to mimic rheumatoid conditions (e.g. rheumatoid arthritis), but are serologically different, as rheumatoid factor is usually negative.
There is a very strong correlation between these conditions and the MHC class I: HLA-B27.
  • However, it is important to remember that 5-10% of the population have this variant of HLA, and most do NOT have spondyloarthritis!

Beware of spondyloarthritis being misdiagnosed as the much more common mechanical back pain.

Epidemiology & Aetiology

  • Aetiology is essentially unknown
  • Associated with HLA-B27
  • Sometimes associated with other disorders – such as Crohn’s disease, UC, chlamydial urethritis, psoriasis.
    • There is often a lot of overlap of symptoms with psoriasis
Ankylosing spondylitis is the major disorder of the spondyloarthritides. It is relatively uncommon and 90% of cases are associated with HLA-B27. Of these, 1-2% have full blown AS, and up to 15% have some symptoms of AS.
  • 15-20% risk of the condition if there is a known first degree relative with the disorder
  • The prevalence of AS varies between races. HLA-B27 is particularly common in caucasians, but uncommon in black Africans, and Japanese populations.
  • Prevalence of 0.1 – 2%
  • Peka age of onset is 20-30
  • M:F is 3:1
    • But men tend to present earlier – at age 16, the M:F is 6:1
    • The disease is also often milder in women


  • Spondylitis – inflammation of the spine
  • Spondylosis – degenerative osteoarthritis changes
  • Ankylosis – stiffness in a joint


Inflammation first occurs around the enthesis – this is the site where ligaments attach to bone. As the inflammation heals, there is new bone formation in the ligament, as sclerosis of the underlying bone. (NB – sclerosis is thickening or hardening)
Eventually, there may be fusion of the vertebral bodies – which prevents flexion and rotation. This is particularly disabling when it occurs in the vertebral spine. Some patients will develop fixed spinal deformities. This is sometimes referred to as bamboo spine. Also, in sever, late disease, the posture of a patient with AS may be referred to as question mark posture – as the neck becomes hyperextended, and there is severe kyphosis of the thoracic spine. This can make forward vision difficult.
The earliest changes are usually in the sacro-iliac joints.

Clinical features

Usually begins before the age of 30. Symptoms are often subtle and insidious at the onset.
  • Episodic Pain – usually in the buttocks and/or lower back in the late teenage years or early 20’s in the first sign. The pain is:
    • Worse in the morning
    • Relieved by exercise
    • May wake the patient during the night – particularly in the second half of the night – after about 2am.
    • May be felt in the buttocks – especially if the sacroiliac joints are affected
  • Spinal stiffness – can be measured with Schoeber’s test:
    • Measure 10cm above the dimples of Venus with the patient standing upright. Place a dot here. As the patient to flex forward (touch their toes). Then re-measure the gap with the patient in this position. Normally, the gap should increase to >15cm. In AS, the gap increases less than this
    • Stiffness is typically worse in the mornings
  • Fever and weight loss may occur during episodes of pain
  • Diagnosis often missed due to lack of symptoms between episodes
  • Retention of lumbar lordosis in spinal flexion
  • Paraspinal muscle wasting (occurs later)
  • You may get costo-vertebral joint involvement – which can cause reduced chest expansion and anterior chest pain.
  • No radiological abnormalities in early stages
  • Late stages
    • Increased thoracic kyphosis – “question mark posture”
  • May also have peripheral joint symptoms
Systemic manifestations / associations
  • Peripheral osteoarthritis – 30% of patients. Pathologically the same as osteoarthritis, but has an unusual distribution. Usually the hands are spared, but the lower limbs and shoulder joints are particularly badly affected.
    • Asymmetrical
  • Uveitis – inflammation of the inner parts of the eye. Usually in this case, anterior parts of the eye, including the iris and ciliary body
    • Acutely painful red eye with photophobia
    • 20-30% of patients
    • Of all patients who present with anterior uveitis – up to 50% will go on to develop AS
  • Cutaneous lesions – that are identical to pustular psoriasis
  • Aortic incompetence (in 1-2% of cases of AS) and other cardiovascular complications
  • Respiratroy complications
    • Restrictive lung disease
    • Pulmonary fibrosis
  • Inflammatory bowel disease (Crohn’s, UC)
  • Peripheral enthesitis
  • Neurological complications
  • Increase risk fo osteoporosis
    • DEXA scans often underestimate the risk in AS

Examining for AS

  • In the early stages of the disease, you may be able to elicit pain by pressing on the lower portion of the sacrum, whilst the patient is laid flat, face down.
  • Schoeber’s Test – as described above
  • Examiner peripheries for enthesitis
  • Check eyes for uveitis
  • Assess lumbar forward flexion
  • Assessment of chest expansion


Diagnosis is often delayed and difficult, due to the insidious and often fairly mild features of at symptom onset, and the broad range of differentials.

Consider AS particularly in patients with chronic back pain and:

  • Aged under 30
  • Morning stiffness >30 minutes
  • Pain that improves with exercise but not with rest
  • Buttock pain
  • Previous anterior uveitis

Diagnosis can be made using the modified New York criteria. 

Diagnosis requires any of:

  • x1 clinical criteria + radiological criteria met
  • x3 clinical criteria present
  • Radiological criteria present

Diagnosis does not require radiological evidence

Criteria include:

  • Clinical criteria
    • Low back pain >3 months, improves with exercise, not relieved by rest
    • Limited chest expansion relative to normal values for age and sex
    • Limited lumbar spine motion in both the fontal and sagittal planes
  • Radiological criteria – sacroiliitis on x-ray

Differential diagnosis

Differentials are broad and I highly recommend reading the lower back pain article for an overview of assessing lower back pain.

Differentials include:


There is no specific diagnostic investigations. Tests can help to rule out other causes, and x-rays can be used as part of the modified New York criteria to assist in making a diagnosis (see above).

  • Bloods – ESR and CRP may be raised, but are often normal
  • HLA testing – not really much use due to high incidence of HLA-B27 in normal population
  • X-Ray – usually normal in early disease. Later signs may include:
    • Sacroiliac joint margins lose definition – as they have become eroded and sclerotic.
    • Blurring of upper and lower rims of vertebrae – particularly in thoracolumbar junction. This is best seen on a Lateral X-ray
    • Syndesmophytes – these are boney lesions in the enthesis, as a result of enthesitis. They tend to be vertically orientated, and not beak-shaped, unlike osteophytes (seen in spondylosis), and also the disc is preserved (again, unlike spondylosis)
    • Joint fusion – may be seen in late disease. Sacroiliac, and costovertebral (reducing chest expansion), and intervertebral.
    • Together, these changes are sometimes referred to as “bamboo spine”
X-ray of advanced ankylosing spondylitis
X-ray of advanced ankylosing spondylitis

MRI is good at detecting very early changes of sacroiliitis, and being increasingly used in AS for this purpose.

CT scan can better detect some of the bony changes seen in late disease on x-ray.


  • AS is a chronic, life-long condition. Treatment aims to reduce symptoms and maximise function.
  • All patients with newly diagnoses Ankylosing spondylitis should be referred to a rheumatologist.
  • The basic treatment is exercise – this reduces long-term disability and other problems.
  • Early diagnosis is important – this allows the regimen of exercises to be implemented early. Spinal exercises should be performed in the morning.
  • Without exercise, patients are more likely to develop wasted paraspinal muscles, and irreversible kyphosis.
  • Physiotherapy referral should be made early to guide this process
  • Sleeping on a firm mattress with a thin pillow reduced the risk of kyphosis
  • Hypotherapy and swimming may also be useful to maintain mobility
During an inflammatory episode, stiffness and pain may prevent exercise. During these episodes, you may want to use an NSAID – often a long acting one, given at night helps to reduce pain, help sleeping, and aid exercise the next morning.
  • Peripheral arthritis is managed with NSAID’s or local steroid injections.
  • NSAIDs have been shown to effectively reduced symptoms and maintain function
  • DMARDs – such as sulfasalazine or methotrexate – as used in other inflammatory arthritis conditions have, unfortunately, not been shown to be of benefit in ankylosing spondylitis
  • TNF-α therapy is useful in severe disease, and can reduce inflammation. But the inflammation will return as soon as treatment is stopped.
    • e.g. etanercept and adlimumab
    • Should only be used under the supervision of a rheumatologist
    • Can increase the risk of serious infections


  • Rarely used, but can be used to correct spinal deformities

Preventative actions


With early diagnosis, and good exercise compliance, prognosis is generally good, but there is wide variability. Up to 80% of patients remain well enough to stay in full time employment. There may be general long-term back stiffness, but disability is rare.
  • Long-term prognosis can be predicted by the level of disability at 10 years after diagnosis – those with only mild disease at 10 years, have a 75% of never progressing to severe disease
  • Poor prognostic indicators:
    • Peripheral joint involvement
    • Young age of onset
    • Elevated ESR
    • Poor response to NSAIDs
  • Mortality is increased compared to the general population
    • Increased risk of MI and stroke
    • Increased risk of malignancy
    • Increased risk of poor psychological health as a result of pain and disability
Apart from the HLA-B27, there is no direct risk of passing on AS. Thus children with an HLA-B27 positive parent, have a 50% chance having the variant themselves, and then are at the same risk as any other person with this variant of having AS (15% chance of some symptoms, 1-2% chance of full diagnosed AS)


  • Ankylosing spondylitis – AS – patient.info
  • Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
  • Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
  • Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy

Read more about our sources

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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