Psoriatic arthritis is an inflammatory joint disease closely associated with
psoriasis, which affects the joints and tendons. ‘Inflammatory arthritis’ means
that there is inflammation present in the affected joints, rather than just wear
and tear. It can be difficult to diagnose, as symptoms can be similar to other
types of arthritis, and a patient does not necessarily have to have psoriasis to
develop it. It is also possible for people with psoriasis to develop a different
type of arthritis (such as rheumatoid arthritis or osteoarthritis); the fact
that they have psoriasis does not alone mean their arthritis is psoriatic.
How is it diagnosed?
At present there are no definitive guidelines for diagnosing psoriatic
arthritis; a doctor will make a diagnosis based on symptoms and medical history,
and by ruling out other conditions. Usually, a blood test will be carried out to
test for rheumatoid factor (the antibody found in rheumatoid arthritis). This is
usually negative in people with psoriatic arthritis, although a positive result
can be due to causes other than rheumatoid arthritis. A doctor may also use X
Rays, ultrasounds or other scans, such as an MRI to look at the patient’s
joints. These scans often show inflammation or areas of new bone growth with
poorly-defined edges in people with psoriatic arthritis.
Traditionally, the Moll and Wright (1973) criteria have been used to diagnose
psoriatic arthritis. The criteria are: an inflammatory arthritis, the presence
of psoriasis, and a blood test negative for rheumatoid factor. Although this
criteria set is still used, it does have limitations, for example, psoriatic
arthritis can occur without there being current psoriasis on the skin.
CASPAR Criteria
More recently, the ClASsification of Psoriatic ARthritis (CASPAR) study group
has compiled a more sensitive and specific criteria set. This consists of the
presence of an inflammatory condition in a joint, the spine, or entheses (the
point where tendons or ligaments join to bone), plus at least three points from
the following:
Current psoriasis (2 points)
A personal or family history of psoriasis (in the absence of current
psoriasis) (1 point)
Dactylitis (swelling of digits) (1 point)
Nail dystrophy (pitting or ridging of nails) (1 point)
Negative rheumatoid factor (1 point)
Radiographic evidence of new bone formation (1 point)
Misdiagnosis of symptoms
Due to the similarity of symptoms, psoriatic arthritis could be mistaken for
another type of arthritis, causing confusion when blood tests are negative for
rheumatoid factor. Those who are young or fairly active may have tenderness or
swelling put down to sports injuries, similarly, back pain is often dismissed in
people of all ages as a part of general wear and tear. Nail changes such as
pitting, discolouration or the formation of ridges is particularly common in
people with psoriatic arthritis, and can occur even when there is no psoriasis
on the skin. Without psoriasis of the skin, nail changes could be misdiagnosed
as fungal infections or vitamin deficiencies. Pain or swelling in the feet,
heels and toes could be misdiagnosed as gout.
Anybody with current psoriasis or a family history of the condition should
request to see a Rheumatologist if they experience a swollen finger or toe with
no explanation, pain or tenderness in the joints (especially of the hands and
feet), recurring injuries or pain where tendons join to bone (such as tennis
elbow or Achilles tendonitis), uveitis or iritis (inflammatory eye conditions).
Pain or stiffness in the neck, back or lower back that improves with movement
and is not relieved by rest can also be a sign of psoriatic arthritis.
