Summary
Ankylosing spondylitis (spondyloarthritis), a type of seronegative spondyloarthropathy, is a chronic inflammatory disease of the axial skeleton that leads to partial or even complete fusion and rigidity of the spine. Males are disproportionately affected and upwards of 90% of patients are positive for the HLA-B27 genotype, which predisposes to the disease. The most characteristic early finding is pain and stiffness in the neck and lower back, caused by inflammation of the vertebral column and the sacroiliac joints. The pain typically improves with activity and is especially prominent at night. Other articular findings include tenderness to percussion and displacement of the sacroiliac joints (Mennell's sign), as well as limited spine mobility, which can progress to restrictive pulmonary disease. The most common extra-articular manifestation is acute, unilateral anterior uveitis. Diagnosis is primarily based on symptoms and x-ray of the sacroiliac joints, with HLA-B27 testing and MRI reserved for inconclusive cases. There is no curative treatment, but regular physiotherapy can slow progression of the disease. Additionally, NSAIDs and/or tumor necrosis factor-α inhibitors may improve symptoms. In severe cases, surgery may be considered to improve quality of life.
Epidemiology
- Sex: ♂ > ♀ (3:1)
- Age: 15–40 years
- Lifetime prevalence in the US: ∼0.5%
References:[1][2]
Epidemiological data refers to the US, unless otherwise specified.
Etiology
- Genetic predisposition: 90–95% of patients are HLA-B27 positive. [1]
Clinical features
Articular symptoms
-
Most common presenting symptoms: back and neck pain
- Gradual onset of dull pain that progresses slowly
- Morning stiffness that improves with activity
- Pain is independent of positioning; , also appears at night
- Tenderness over the sacroiliac joints
- Limited mobility of the spine (especially reduced forward lumbar flexion)
- Inflammatory enthesitis (e.g., of the Achilles tendon, iliac crests, tibial tuberosities): painful on palpation
- Dactylitis
- Arthritis outside the spine (hip, shoulder, knee joint)
Extra-articular manifestations
- Most common: acute, unilateral anterior uveitis (∼ 25% of cases)
- Fatigue, weakness, fever, weight loss
- Restrictive pulmonary disease due to decreased mobility of the spine and thorax
- Gastrointestinal symptoms: associated with chronic inflammatory bowel disease (∼ 5–10% of cases, see also: ulcerative colitis or Crohn disease)
- Prostatitis
- Rare
- Cardiac: aortic root inflammation and subsequent aortic valve insufficiency, atrioventricular blocks
- Kidney: IgA-nephropathy
References:[1][2]
Diagnostics
Diagnostic approach
- Physical examination, patient history, and pelvic x-ray: If results are conclusive, no additional testing is required!
- If inconclusive → HLA-B27 testing
- If still inconclusive → pelvic MRI
Clinical tests
-
Chest expansion measurement: to monitor disease severity
-
Method: measure chest circumference in full expiration and inspiration
- Pathological difference: < 2 cm
- Physiological difference: > 5 cm
-
Method: measure chest circumference in full expiration and inspiration
- Spine mobility tests
-
Examination of the hip [3]
- Mennell sign: tenderness to percussion and pain on displacement of the sacroiliac joints
- FABER test: FABER (Flexion, ABduction, and External Rotation) provokes pain in the ipsilateral hip
The degree of decrease in chest expansion is an important determinant of disease severity.
Laboratory findings
- ↑ CRP and ESR
- Auto-antibodies (e.g., rheumatoid factor, antinuclear antibodies) are negative
-
HLA-B27 positive in 90–95% of cases
- However, < 5% of HLA-B27 positive individuals have ankylosing spondylitis.
Imaging
X-ray
- Helps confirm a diagnosis and evaluate the severity of disease
- Changes are generally more evident in later disease.
- The changes usually occur symmetrically.
-
Pelvis (best initial test): to examine the sacroiliac joints
- Signs of sacroiliitis, including ankylosis (fusion of the articular surfaces)
-
Spine
- Loss of lordosis with increasing abnormal straightening of the spine
- Sclerosis of the vertebral ligamentous apparatus
- Syndesmophytes resulting in a so-called 'bamboo spine' in anteroposterior radiograph in the later stages (see the table in “Differential diagnosis” below)
- Signs of spondyloarthritis, including ankylosis of intervertebral joints [4]
- Thorax: ankylosis of costosternal and costovertebral joints
Mild courses may only exhibit inflammatory changes in the sacroiliac joints on x-ray after a number of years.
MRI
- More sensitive than CT scan for detecting sacroiliitis [5]
- Best method for early detection
References:[1][6][7]
Differential diagnoses
- Mechanical low back pain
- Fibromyalgia
- Disc prolapse
- Vertebral osteomyelitis
- Other spondyloarthritides (e.g., reactive arthritis, psoriasis arthritis, arthritis associated with inflammatory bowel disease)
-
Diffuse idiopathic skeletal hyperostosis (DISH; also called Forestier's disease or hyperostotic spondylosis)
- Definition: degenerative disease of the vertebral column (especially the thoracic and lumbar spine), which is characterized by calcification and ossification of spinal ligaments and entheses
- Epidemiology
-
Clinical presentation
- Limited mobility
- Mild or even no pain at all
-
Diagnosis
-
X-ray of the spine
- Formation of osteophytes (see table below)
- No sacroiliitis
-
X-ray of the spine
- Treatment: symptomatic
- Osteophytes of the spine
Syndesmophytes | Osteophytes | |
---|---|---|
Definition |
|
|
Radiographic features |
|
|
Etiology |
|
|
Syndesmophytes grow vertically, as opposed to osteophytes, which grow horizontally!
References:[9][10][11]
The differential diagnoses listed here are not exhaustive.
Treatment
-
Physical therapy
- Consistent and rigorous physical therapy
- Independent exercises
-
Medical therapy
- First choice: NSAIDs (e.g., indomethacin)
- Additional options
- Tumor necrosis factor-α inhibitors (e.g., etanercept, adalimumab) [12]
- In case of peripheral arthritis: DMARDs (especially sulfasalazine)
- In severe cases: temporary, intra-articular glucocorticoids
- Surgery: in severe cases to improve quality of life
Physical therapy is the most important treatment modality!References:[1][13]
Complications
- Complete fusion of the spine → severely limited mobility
- Increased risk of osteoporosis → pathological fractures and possibly spinal cord injury
- Restricted chest expansion and spine mobility → breathing difficulties
References:[1][2]
We list the most important complications. The selection is not exhaustive.