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Tips on diagnosing spondyloarthritis

Musculoskeletal GPSI Dr Louise Warburton offers her tips on diagnosing this closely related group of inflammatory diseases

Musculoskeletal GPSI Dr Louise Warburton offers her tips on diagnosing this closely related group of inflammatory diseases

1. The incidence of the spondyloarthritides (SpAs) is as high as 1-2% in Europe, making them as common as rheumatoid arthritis. They are made up of a group of illnesses: reactive arthritis, psoriatic arthritis (PsA), ankylosing spondylitis (AS), and arthritis associated with IBD.

2 About 80% of patients with AS develop back pain before age 30.

However, the early stages are often subtle and difficult to diagnose. There can be a delay of 10 years between the first signs and full-blown disease, which is classified using the 1984 Modified New York Criteria:

• low back pain and stiffness for longer than three months which improves with exercise but is not relieved by rest

• restriction of motion of the lumbar spine in both the sagittal and frontal planes (ask the patient to try to touch their toes and try side-bending)

• restriction of chest expansion relative to normal values correlated for age and sex.

Radiological criterion:

• sacroiliitis grade 2 bilaterally or grade 3 unilaterally.

Definite AS is present if the radiological criterion is present with at least one clinical criterion.

Men are two to three times more likely to be affected by AS than women and there is an association with the HLA-B27 genotype (see tip 4 below).

3 Inflammatory back pain (IBP) is the other key clinical symptom of AS.

This can also be present in other SpA subgroups with axial (spinal) involvement. Indicators of IBP are: insidious onset; age 40 or younger at onset; duration of back pain more than three months; morning stiffness; and improvement with exercise.

Important pointers in the history are:

• morning back stiffness of more than 30 minutes; ask the patient if they can get their socks on in the morning or reach up to a high shelf when they first get up

• back pain which improves with exercise and is made worse with rest

• waking because of back pain in the second half of the night, often when the patient tries to turn over

• alternating buttock pain because of sacroiliitis.

IBP is said to be present if at least two of the four parameters are fulfilled.

4 Testing for the HLA-B27 genotype is useful in patients with IBP.

The prevalence of HLA-B27 in European populations and the US is 5-14%. There is very strong association between HLA-B27 and AS of between 80-95% but there is no association with mechanical back pain.

Although positive HLA-B27 alone is not enough to diagnose AS in patients with chronic back pain – disease probability is 32% – HLA-B27 in combination with the other parameters of IBP, discussed above, is highly indicative of AS.

5 Acute-phase reactants such as C-reactive protein and ESR have limited value as diagnostic tests for AS.

A substantial proportion of AS patients will have normal values.

6 Plain X-rays have limited value in diagnosing sacroiliitis.

CT is more sensitive in detecting chronic changes such as sclerosis, erosions and ankylosis in the sacroiliac joints. MRI of the sacroiliac joints is a very sensitive imaging tool because both active and chronic changes associated with sacroiliitis can be visualised.

7 The skin and joint diseases in PsA do not necessarily present at the same time.

PsA is an inflammatory arthritis, which is generally associated with skin psoriasis. In fact, each manifestation may be seen separately in first-degree relatives in isolation, which can lead to difficulties in diagnosis. Therefore, always ask about a family history of psoriasis.

Historically it is classified according to the Moll and Wright criteria and these are important for picking up early presentations:

• distal interphalangeal (DIP) joint hand arthropathy

• symmetrical arthritis indistinguishable from RA but with negative rheumatoid factor.

• asymmetric, pauciarticular arthritis with small joint involvement

• AS pattern with or without peripheral arthritis.

Don't forget to examine the nails for the typical, and often difficult to spot, psoriatic pitting.

8 Patients with PsA will often have had swollen toes for months or even years before being diagnosed.

They will have often already seen a number of health professionals, such as podiatrists, who have failed to make a diagnosis. In terms of diagnostic features, it is important to realise that swollen digits (sausage digits) are common in PsA.

These are due to dactylitis – inflammation of the joints, tendon insertions (entheses) and the tendons in the digit causing global swelling.

Enthesis and osteitis are universal features of PsA-related disease at presentation. On MRI scanning it is possible to see inflammation in the entheses and bone inflammation (osteitis) adjacent to the entheses. These pathologies then cause synovitis and joint swelling.

9 Be aware of other features associated with PsA and SpAs:

• chest pain due to costochondritis – lots of patients present with this but the link to their arthritis is not made

• uveitis (iritis)

• fatigue or malaise – very prominent in SpAs

• aortitis

• pleuritis.

10 Remember this group of arthritides can overlap and a patient may present with symptoms of more than one subgroup.

It is now thought that in many patients with SpA the disease was actually unmasked by exposure to an infective agent, be this gut-related such as campylobacter or STD-associated such as chlamydia, causing the classical reactive arthritis.

Reactive arthritis presents with similar clinical features to PsA or AS and the incidence of HLA-B27 is much higher in these patients than in the normal population.

In these patients, the reactive arthritis is actually the early phase of their spondyloarthritis.

Dr Louise Warburton is a GP in Shropshire and a GPSI in musculoskeletal medicine

Competing interests: None declared

Psoriatic arthritis

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