Diagnosis and Classification of Spondyloarthropathies
Spondyloarthropathy is a chronic form of inflammatory arthritis which affects around 0.5-1.5 percent of the Western population. It is a family of diseases, which includes axial spondyloarthritis (also known as ankylosing spondylitis), psoriatic arthritis, reactive arthritis, enteropathic arthritis and undifferentiated arthritis. These conditions affect both the axial and peripheral skeleton and have various extra-articular features.
Diagnosis of spondyloarthropathy is a complex process and must be given by a specialist (i.e. a rheumatologist). However, because of the complexities in identifying these conditions, diagnosis is often delayed. For instance, axial spondyloarthritis often goes undiagnosed for five to ten years from symptom onset. This is significant because early diagnosis of axial spondyloarthritis results in better outcomes in terms of disease activity, function, spinal mobility and radiographic damage, as well as a better response to treatment.
Significantly for physiotherapists, a prior diagnosis of mechanical back pain has been found to be an independent factor related to delays in diagnosis. It is, therefore, necessary to be able to differentiate between mechanical and inflammatory back pain. For more information on differentiating these types of pain, please click here.
Various classification systems exist to improve early detection of spondyloarthropathy. This page will explore, in particular, the ASAS classification for axial spondyloarthritis, which classifies spondyloarthritis as either axial (radiographic or non-radiographic) or peripheral, as well as the CASPAR criteria for psoriatic arthritis.
The following video provides insight from patients on the impact of delayed diagnosis of axial spondyloarthritis.
The next video discusses the diagnosis of inflammatory back pain from a medical perspective.
Axial spondyloarthritis is the prototypic form of spondyloarthropathy. The modified New York Classification Criteria (mNYCC) was previously used to diagnose axial spondyloarthritis. The mNYCC includes clinical and radiological criteria:
|The appearance of the sacroiliac joints on x-ray are given a grade of 0 to 4:
||To meet the radiological criteria for axial spondyloarthritis, a patient has:
Grade 2, 3 or 4 sacroiliitis on both sides
Grade 3 or 4 sacroiliitis on one side
As well as meeting the radiological criteria, the patient must fulfil at least one of the following clinical criteria:
However, structural damage is estimated to take between six and ten years to develop from symptom onset and in some cases, it may not develop at all. Thus, the mNYCC is unable to detect patients with early signs of axial inflammation. This has added to the delay in diagnosis of axial spondyloarthritis.
The creation of the Assessment of Spondyloarthritis International Society Axial Spondyloarthritis (ASAS) classification criteria in 2009 has been considered a positive step forwards for research on spondyloarthropathy. This classification criteria have, for the first time, enabled earlier identification of axial spondyloarthritis through magnetic resonance imaging (MRI).
The ASAS also created another subgroup of axial spondyloarthritis, labelled non-radiographic spondyloarthritis (nrAxSpA). A diagnosis of nrAxSpA can be given patients who fulfil certain criteria, but who do not have radiographic sacroiliitis.
It is, however, important to note that these criteria are not diagnostic in themselves. The clinician still needs to consider the whole picture.
The 2009 ASAS criteria essentially incorporate two arms, an imagining arm and a clinical arm. The criteria are as follows:
|Patients who have had back pain for more than 3 months, with an age of onset less than 45 years, as well as:|
|Imaging Arm||OR||Clinical Arm|
|Sacroiliitis on imaging (i.e. active (acute) inflammation on MRI that is highly suggestive of sacroiliitis or definite radiographic sacroiliitis according to mNYCC)
1 or more feature of spondyloarthropathy
2 or more features of spondyloarthropathy
ASAS features of spondyloarthropathy are:
- Inflammatory back pain
- Enthesitis (heel) (i.e. inflammation of the site where tendons / ligaments insert into bone)
- Uveitis (inflammation of the uvea)
- Dactylitis (whole digit swelling)
- Crohn’s / colitis
- Good response to NSAIDs
- Family history of spondyloarthropathy
- HLA-B27 positive
- Elevated CRP
In 2011, the ASAS criteria were extended to better include peripheral manifestations of the disease. Psoriatic arthritis, reactive arthritis, and enteropathic arthritis are largely considered peripheral conditions, although there may be some features that overlap with axial spondyloarthritis (radiographic and non-radiographic) and vice versa. To be classified as having peripheral spondyloarthritis, a patient must have either:
|Arthritis OR enthesitis OR dactylitis, and fulfil one of the two following categories:|
|One or more of the following:||OR||Two or more of the following:|
These criteria were found to have a sensitivity of 77.8 percent and a specificity of 82.9 percent.
Like axial spondyloarthritis, diagnosing psoriatic arthritis is challenging. This is significant as even a six-month delay from initial symptoms to the first rheumatology appointment can contribute to peripheral joint erosions and poorer long-term physical function. While various classification systems have been used to identify psoriatic arthritis, the 2006 Criteria of the Classification of Psoriatic Arthritis (CASPAR) has helped to increase recognition of this condition by medical practitioners. The CASPAR tool has been found to have a specificity of 98.7 percent and sensitivity of 91.4 percent. The criteria is defined as follows:
|A patient must have an inflammatory articular disease (joint, spine or entheseal) PLUS fulfil 3 or more of the following 5 categories:|
|2. Typical psoriatic nail dystrophy including, onycholysis, pitting and hyperkeratosis, which can be observed on physical examination|
|3. A negative test for rheumatoid factor|
|4. Either current dactylitis or a history of dactylitis|
|5. Radiographic evidence of juxta-articular new bone formation, which appears as poorly defined ossification near joint margins (excluding osteophyte formation) on hand or foot x-rays|
NB: The presence of current psoriasis is assigned two points, while all other clinical features are assigned one point.
Recognition and Referral of Spondyloarthropathy
Diagnosis of spondyloarthropathy is made by a specialist, but it is important for physiotherapists to be able to detect and refer patients who may present with concerning features to the appropriate services. The "NICE Guidelines on Spondyloarthritis in over 16s" remind clinicians in cases of suspected spondyloarthropathy that:
- Symptoms of spondyloarthritis can be diverse and difficult to identify
- Signs and symptoms may be musculoskeletal (i.e. inflammatory back pain, enthesitis, dactylitis) or extra-articular (i.e. uveitis, psoriasis)
- Risk factors include recent genitourinary infection and a family history of spondyloarthritis or psoriasis
- Axial spondyloarthritis affects a similar number of women as men
- It can occur in individuals who are not HLA-B27 positive
- It may be present even if there is no evidence of x-ray
These guidelines recommend referral to a rheumatologist for suspected axial spondyloarthritis if a patient has had low back pain for more than three months that started before the age of 45 years as well as FOUR or more of the following criteria:
- low back pain that started before the age of 35 years - this increases the likelihood that the patient's back pain is due to spondyloarthritis when compared to low back pain that started between the age of 35 and 44 years
- pain / symptoms that wake the patient during the second half of the night
- buttock pain
- pain that improves with movement
- pain that improves within 48 hours of taking non-steroidal anti-inflammatory drugs (NSAIDs)
- patients who have a first-degree relative with spondyloarthritis
- patients who have current or past arthritis
- patients who have current or past enthesitis
- patients who have current or past psoriasis
If three of the additional criteria are present, NICE Guidelines recommend that an HLA‑B27 test is performed. If this test is positive, the patient would need to be referred to a rheumatologist for assessment.
The full NICE Guidelines on when to refer patients with suspected spondyloarthropathy are available here.
While classification systems exist to aid the identification of spondyloarthropathy, there is no gold standard for diagnosis of this family of conditions. Because of the complexities and variety of symptoms, diagnosis of these conditions can be lengthy and delayed.
Diagnosis is made based on the patient’s history, clinical examination, laboratory tests, imaging, and an index of suspicion around spondyloarthropathy.
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