Ankylosing Spondylitis
Musculoskeletal
Question 66 of 180
A 45 year old man presents to clinic with worsening lower back pain. The pain is worse in the morning and improves throughout the day with exercise. The pain spreads to his buttocks and is associated with stiffness. He recalls having this pain since he was in his early twenties, and it has never resolved. What is the diagnosis?
Answer:
Ankylosing spondylitis is suggested by X-ray changes of the sacroiliac joints and spine, including sacroiliitis, sclerosis (thickening of bone), erosions, and partial or total ankylosis (fusion of joints). Bamboo spine is a pathognomonic radiographic feature seen in ankylosing spondylitis that occurs as a result of vertebral body fusion by marginal syndesmophytes. It is often accompanied by fusion of the posterior vertebral elements as well.Ankylosing Spondylitis
Musculoskeletal
Last Updated: 12th February 2021
Ankylosing spondylitis (radiographic axial spondyloarthritis) is axial spondyloarthritis characterised by sacroiliitis on x-ray.
Features of ankylosing spondylitis include:
- Chronic back pain (often inflammatory in nature) and stiffness that improves with exercise, not rest.
- Sacroiliac joint and spinal fusion. New bone formation leads to sacroiliac joint ankylosis and the formation of syndesmophytes (bony growths in intervertebral joint ligaments) in the spine.
- Arthritis and enthesitis — the most common peripheral manifestations (predominantly in the lower limbs with asymmetrical distribution).
- Dactylitis (swelling of a finger or toe).
- Fatigue.
- Extra-articular manifestations (for example anterior uveitis, psoriasis, inflammatory bowel disease).
Risk factors
- Sex
- Around twice as many men have ankylosing spondylitis compared with women.
- Age
- It most commonly begins between 20 and 30 years of age, with 90–95% of people aged less than 45 years at disease onset.
- Familial association
- More than 90% heritability has been estimated for axial spondyloarthritis; the most important genetic risk factor is human leukocyte antigen B27 (HLA-B27).
Clinical features
Recognise that spondyloarthritis can have diverse symptoms and be difficult to identify which can lead to delayed or missed diagnoses.
Suspect ankylosing spondylitis in anyone with chronic or recurrent low back pain, fatigue, and stiffness, especially if:
- The person is 45 years of age or younger.
- The back pain has been present for more than 3 months.
- Back pain and stiffness is inflammatory (rather than mechanical) and worse in the morning (lasting for more than 30 minutes), improving with movement.
- They have current or previous:
- Buttock pain — sometimes on one side and sometimes on the other.
- Pain in the thoracic or cervical spine.
- Arthritis, predominantly asymmetric and peripheral.
- Enthesitis.
- Anterior uveitis — this presents as an acutely painful red eye with photophobia or blurred vision.
- Psoriasis or inflammatory bowel disease, or genitourinary infection.
- Symptoms wake them in the night (particularly during the second half).
- Symptoms respond to a course of nonsteroidal anti-inflammatory drugs (NSAIDs) within 48 hours.
- There is a family history of ankylosing spondylitis or spondyloarthritis.
- Other conditions with similar presentations have been excluded.
Differential diagnosis
Differential diagnoses of axial spondyloarthritis include:
- Degenerative or mechanical problems (most common) — for example degenerative disc disease, spondylosis, congenital vertebral anomalies, degenerative changes in the intervertebral (facet) joints, osteoarthritis of sacroiliac joints.
- Fractures.
- Infectious sacroiliitis.
- Bone metastasis.
- Primary bone tumours.
- Spinal stenosis.
- Hypermobility.
Investigations
Refer to a rheumatologist for confirmation of the diagnosis as this can be difficult. Clinical features and diagnostic tests for ankylosing spondylitis can help make the diagnosis, but no symptom, sign, or test result in isolation is useful for diagnosis.
- Bloods
- Raised CRP/ESR
- Mild normochromic normocytic anaemia
- X-ray
- Ankylosing spondylitis is suggested by X-ray changes of the sacroiliac joints and spine, including sacroiliitis, sclerosis (thickening of bone), erosions, and partial or total ankylosis (fusion of joints).
- MRI
- In some people with symptoms of ankylosing spondylitis, inflammation of the sacroiliac joints can be detected on MRI despite an absence of changes on X-ray.
- HLA-B27 test
Management
- Consider prescribing a nonsteroidal anti-inflammatory drug (NSAID) while waiting for referral. If NSAIDs are contraindicated, consider prescribing a standard analgesic (for example paracetamol with or without codeine). Note that non-NSAID analgesics will not control inflammation.
Complications
Complications of axial spondyloarthritis include:
- Ankylosis or spinal fusion resulting from new bone formation.
- Spinal fractures.
- Anterior uveitis (iritis).
- Osteoporosis.
- Cardiac complications:
- The risk of cardiovascular disease is thought to be increased in people with spondyloarthritis, due to the systemic inflammatory nature of the condition. Long-term use of NSAIDs may also contribute to this risk, although it is unclear in this specific population. It is therefore particularly important to identify and manage modifiable cardiovascular risk factors.
- Cardiac complications of ankylosing spondylitis also include aortic and non-aortic valvular heart disease and congestive heart failure. Arrhythmias may also be present (for example ventricular and supraventricular extrasystoles).
- Lung involvement such as restrictive pulmonary disease and apical fibrosis. Dyspnoea may occur as a result of costovertebral involvement decreasing vital capacity.
- Neurological involvement from vertebral fracture, dislocation, or cauda equina syndrome (sensory disturbance in lower limbs and perineum).
- Adverse effects from drugs used to treat the condition, for example NSAIDs (gastritis, ulcers, renal effects), biological DMARDs (infection, immunosuppression, malignancy).
- Decreased quality of life and work productivity due to pain, stiffness, fatigue, reduction in spinal mobility and physical function, and sleep problems.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
