Psoriatic arthritis (PsA) appears to happen when an overactive immune system mistakenly attacks healthy tissue. However, it is not yet clear why some people with psoriasis develop PsA while others do not.
Diagnosing psoriatic arthritis
Psoriatic arthritis can affect the joints of the hands and feet.
There is no definitive test for PsA.
To diagnose the condition, a doctor will:
- take a detailed medical history
- carry out a physical exam
- do some further imaging tests
This information can help a doctor to make a diagnosis and rule out other possible causes.
If a doctor believes a person may have PsA, they will refer them to a rheumatologist, a specialist in joint conditions, for an assessment.
They will often order the following tests to help make a diagnosis:
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels: These blood tests measure inflammation in the body.
- Full blood count, kidney function and electrolytes, and liver function tests.
- MRIs and X-rays of the affected joints: MRI and ultrasound can detect any wearing down and inflammation in joints earlier than X-rays.
- Rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP) antibodies: If a person has these antibodies, a doctor may consider a diagnosis of rheumatoid arthritis rather than PsA.
- Anti-nuclear antibodies (ANA): These antibodies can be present in people with PsA.
Patterns of psoriatic arthritis
Five specific patterns of inflammation can help rheumatologists to manage PsA.
The patterns are:
- Asymmetrical oligoarticular arthritis: This affects four or fewer joints, and symptoms usually affect the feet and other large joints. It does not occur on both sides of the body.
- Symmetrical polyarthritis: This affects five or more joints. These are often the small joints of hands and feet and larger, weight-bearing joints. If it occurs in one joint on the right side of the body, it will also affect the corresponding joint on the left side. It can occasionally look like rheumatoid arthritis.
- Distal arthritis: This affects the small joints closest to the nails in the fingers and toes.
- Arthritis mutilans: This is the most severe, destructive form of PsA. It can result in a shortening of the affected fingers and toes, due to severe bone destruction.
- Spondyloarthritis: This affects the joints of the low back and the pelvis. Back pain and morning stiffness are the main symptoms.
The CASPAR criteria for diagnosis
Diagnosis of PsA should follow the CASPAR criteria.
A person will often have a diagnosis of inflammatory articular disease if their symptoms include:
- tender and swollen joints
- acute stiffness that limits motion, particularly in the morning
For a diagnosis of PsA using the CASPAR criteria, a person must also have at least three points of the following features:
- current active psoriasis (2 points)
- personal history of psoriasis, unless current psoriasis is present (1 point)
- family history of psoriasis, unless current psoriasis is present or there is a personal history of psoriasis (1 point)
- current or previous dactylitis, also known as "sausage fingers," where the fingers or toes are swollen (1 point)
- new bone growth near a joint that is visible on an X-ray (1 point)
- rheumatoid factor (RF) negativity (1 point)
- certain nail problems, such as nail pitting and separation from the nail bed (1 point)
These CASPAR criteria have a specificity of 98.7 percent and sensitivity of 91.4 percent for diagnosing PsA.
When to see a doctor
Symptoms of PsA vary from mild to severe. Generally, people have good and bad days.
Apart from joint pain, tiredness is a common symptom of psoriatic arthritis.
On a good day, symptoms may be barely noticeable. A flare-up, on the other hand, can be extremely painful.
Usually, one or more of the following symptoms will appear:
- general tiredness
- tenderness, pain, and swelling over tendons
- swollen fingers and toes
- joint pain with swelling and stiffness
- reduced range of movement
- stiffness in joints in the morning
- nail changes, including pitting of nails and separation of nails from the nail bed
People with psoriasis who experience persistent pain, swelling, or stiffness in their joints should see a doctor.
It can often take some time to get a diagnosis of PsA. During this time, the person is at risk of progressive joint damage and disability.
However, the long-term outlook for the management of PsA is good, especially if diagnosis is early and the person follows an appropriate treatment plan.
One aim of treatment is to relieve inflammation and swelling.
There are many different treatment options available for PsA, depending on how severe the condition is.
Treatment will aim to:
- reduce symptoms
- slow the progression of the disease
- allow the joints to work as well as possible
- improve the person's quality of life
- prevent or minimize complications
In 2015, two groups of experts, the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) and European League Against Rheumatism (EULAR), made recommendations to help rheumatologists decide on the best course of action for managing PsA.
In general, their recommendations were as follows:
The GRAPPA guidelines recommended using non-steroidal anti-inflammatory drugs (NSAIDs) as a first-line therapy for joints that are painful but not yet at risk of damage.
NSAIDs block the production of prostaglandins, which signal the body's immune system to trigger an inflammatory response.
Common over-the-counter NSAIDs are ibuprofen and naproxen sodium.
Injecting a local corticosteroid injection into affected joints can provide temporary relief from inflammation.
A doctor may introduce a disease-modifying antirheumatic drug (DMARD) to help to slow disease progression. Oral small molecule (OSM) drugs are a type of non-biologic disease-modifying therapy.
Apremilast (Otezla) is one type of OSM drug. Apremilast works by blocking an enzyme that manages immune and inflammatory processes.
Finally, the 2015 guidelines recommended offering a special subclass of DMARDs called tumor necrosis factor inhibitors (TNFIs) if the symptoms did not respond effectively to other DMARDs.
TNFIs work by blocking a specific protein that immune cells produce. This protein signals other cells to start the inflammatory process.
Newer biologics, such as ustekinumab (Stelara), work by blocking two proteins that cause inflammation.
Others, such assecukinumab (Cosentyx), ixekizumab (Taltz), and siliq (Brodalumab) target a different protein.
New treatment guidelines in 2018
In 2018, the American College of Rheumatology and the National Psoriasis Foundation issued new guidelines for the treatment of psoriatic arthritis.
The guidelines recommend a treat-to-target approach for all patients. This means that a treatment option will focus on a specific target.
Doctors may also discuss with the individual the option to use TNFI biologics as a first-line treatment option. They might decide to prescribe these drugs in preference to OSM drugs.
Doctors will continue to prescribe OSM drugs—for example, tofacitinib (Xeljanz)—for people who cannot use TNFI therapy for some reason.
People who should not use TNFI treatment include those with:
- congestive heart failure
- previous serious infections or recurrent infections
- demyelinating disease, or another autoimmune disease, such as lupus
The new guidelines also make a strong recommendation for avoiding or quitting smoking. This is very important, as smoking can trigger psoriasis, PsA, and rheumatoid arthritis.
They also recommend:
- physical therapy
- occupational therapy
- weight loss, where appropriate
A number of other lifestyle choices, dietary factors, and complementary therapies may help to ease the symptoms of PsA. Find out more here.
Psoriatic arthritis is a progressive disease. If left untreated, it will lead to loss of function in the affected joints. However, treatment can relieve symptoms and may slow the progression of the disease.