Ankylosing spondylitis

Summary

Ankylosing spondylitis is an autoimmune, HLA-B27 associated chronic inflammatory disease characterised by inflammation and stiffening of the spine and sacroiliac joints. It is associated with many systemic and ocular features. The most common ocular feature is acute anterior uveitis.

n

Background

n

Ankylosing spondylitis (AS) is a seronegative spondyloarthropathy (alongside psoriatic arthritis, reactive arthritis and enteropathic arthritis), characterised by chronic inflammation and stiffening of the spine and sacroiliac joints. The term ‘seronegative’ means it is rheumatoid factor-negative and anti-CCP-negative.

n

The pathophysiology involves inflammation, calcification and finally ossification of the ligaments and capsules of joints with consequent bony ankylosis of the axial skeleton.

n

Epidemiology

n
• 〜95% of cases are associated with HLA-B27. Patients who are HLA-B27-positive tend to have more severe disease, with earlier onset, greater intensity of inflammation and increased frequency of complications

n

• The male to female ratio is approximately 6:1

n

• The typical age of onset is late adolescence/young adulthood (〜20-30 years of age)

n

Systemic features

n
• Typically presents with insidious onset stiffness and pain in the lower back/buttocks

n

• Spondyloarthritis gradually limits spinal movements, and eventually the spine may become fixed in flexion. Spinal stenosis and fractures may occur

n

• Enthesitis (inflammation at sites where ligaments/tendons attach to bone) e.g. Achilles tendonitis, plantar fasciitis

n

• Radiology of the sacroiliac joints initially shows juxta-articular osteoporosis, and in later stages, sclerosis and bony obliteration of the joint. Calcification of spinal ligaments produces the ‘bamboo spine’ appearance. Radiological changes often appear before clinical symptoms

n

• Cardiac complications are rare, but may include aortic regurgitation and AV node block

n

• Apical pulmonary fibrosis

n

• Amyloidosis

n

n

The clinical features of ankylosing spondylitis can be remembered as “the A’s”:

n
• Apical fibrosis of the lungs

n

• Anterior uveitis

n

• Aortic regurgitation

n

• Achilles tendonitis

n

• AV node block

n

• Amyloidosis

n

Ocular features

n

Acute anterior uveitis (AAU) is the most common ocular feature, occurring in 〜25% of patients with AS. Furthermore, 〜25% of males with AAU will have AS. Either eye is frequently affected at different times, but it is rare for both eyes to be simultaneously affected. There is no association between severity and activity of ocular and joint involvement. Rarely, patients are chronically affected.

nn

Symptoms in AAU consist of rapid-onset of unilateral pain, visual loss, photophobia, redness and watery discharge, sometimes preceded by mild ocular discomfort for several days.

nn

Signs in AAU:

n
• ‘Ciliary injection’ – circumcorneal conjunctival hyperaemia with a violaceous (purplish) hue due to involvement of deeper blood vessels

n

• Visual acuity may be impaired (often only mildly)

n

• Miosis due to pupillary sphincter spasm —> this predisposes to formation of posterior synechiae (adhesions of the iris to the lens). Synechiae formation produces an irregular pupil shape.

n

• Anterior chamber cells – an indicator of inflammation

n

• Aqueous flare – haziness of the normally clear fluid of the anterior chamber, caused by presence of protein due to breakdown of the blood-aqueous barrier

n

• Hypopyon – whitish exudate in the inferior part of the anterior chamber due to presence of inflammatory cells. Fibrinous exudate may be seen in the anterior chamber in severe AAU

n

• Keratic precipitates – deposited on the corneal endothelium composed of inflammatory cells

n

• Iris nodules

n

• Rubeosis iridis (iris neovascularisation) – usually in chronic anterior uveitis

n

Other ocular features associated with AS are:

n
• Scleritis

n

• Episcleritis

n

• Keratitis

n

• Mechanical ptosis

n

n

n

Investigations

n

The most useful investigation in diagnosis AS is a pelvic x-ray. This may show:

n
• Sacroilitis – inflammation and fusion of the sacroiliac joints, subchondral erosions and sclerosis

n

• Squaring of the lumbar vertebra

n

• Vertebral syndesmophytes (bony proliferations) – due to ossification of the spinal ligaments or of the outer fibres of the annulus fibrosus. A late sign of ossification the spinal ligaments is the ‘Bamboo spine’ appearance. Ossification of the supraspinous and interspinous ligaments can produce the ‘Dagger sign’ (a central radiodense line through the vertebrae)

n

Other investigations that may be useful include:

n
• Bloods: raised ESR and CRP (although normal levels do not exclude AS), HLA tissue typing (HLA-B27)

n

• Chest x-ray: showing apical fibrosis

n

• Spirometry: showing a restrictive defect

n

• DEXA scan: osteoporosis

n

Diagnosis

n

AS is diagnosed by radiographic evidence of sacroilitis PLUS ≥1 clinical criterion:

n
• Lower back pain (for >3 months, improved by exercise but not relieved by rest)

n

• Limitation of lumbar spine motion

n

• Limitation of chest expansion

n

Management

n

Conservative:

n
• Regular exercise

n

• Physiotherapy

n

Medical:

n
• 1st-line: NSAIDs (e.g. ibuprofen/naproxen)

n

• 2nd-line: intra-articular corticosteroid injection

n

• If the above aren’t effective, other treatments such as TNF-alpha treatment may be tried

n

• Bisphosphonates (for osteoporosis)

n

Management of anterior uveitis:

n
• Topical steroids (e.g. prednisolone drops)

n

• Cycloplegics (e.g. atropine, cyclopentolate) – dilates the pupil, which helps to relieve pain and photophobia, and prevents posterior synechiae forming

n

References

n
1. Salmon, John F., and Jack J. Kanski. Kanski’s Clinical Ophthalmology: A Systematic Approach. Ninth Edition, Elsevier, 2020.

n

2. Zhu, Wei, et al. ‘Ankylosing Spondylitis: Etiology, Pathogenesis, and Treatments’. Bone Research, vol. 7, Aug. 2019, p. 22. PubMed Central, https://doi.org/10.1038/s41413-019-0057-8.

n

3. Yoshida, Atsushi, et al. ‘Cytomegalovirus Uveitis with Hypopyon Mimicking Bacterial Endophthalmitis’. Case Reports in Ophthalmological Medicine, vol. 2015, 2015, p. 489813. PubMed, https://doi.org/10.1155/2015/489813.

n

4. Agrawal, Rupesh V., et al. ‘Current Approach in Diagnosis and Management of Anterior Uveitis’. Indian Journal of Ophthalmology, vol. 58, no. 1, 2010, pp. 11–19. PubMed Central, https://doi.org/10.4103/0301-4738.58468.

n

5. Gilani, Christopher J., et al. ‘Differentiating Urgent and Emergent Causes of Acute Red Eye for the Emergency Physician’. Western Journal of Emergency Medicine, vol. 18, no. 3, Apr. 2017, p. 509. www.ncbi.nlm.nih.gov, https://doi.org/10.5811/westjem.2016.12.31798.

n