Psoriatic arthritis (PsA) is thought to result from an overactive immune system, which mistakenly attacks healthy tissue. However, it is not yet clear why some people with psoriasis develop PsA while others do not.
Diagnosing psoriatic arthritis
Joint inflammation and swelling is common in the early stages of psoriatic arthritis.
There is no definitive test for PsA. Diagnosis involves taking a detailed patient history, having a physical exam, and some further imaging tests.
Imaging is used to look for inflammation in at least one joint. Doctors then use this information to make a diagnosis by ruling out other causes.
People with suspected PsA should be referred to a rheumatologist, a specialist in joint conditions, for an assessment. A rheumatologist will try to rule out other types of arthritis, such as rheumatoid arthritis, osteoarthritis, and gout.
They will often order the following tests to help confirm a diagnosis:
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level. These are blood tests that 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 will detect any wearing down and inflammation in joints earlier than X-rays.
- Rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP) antibodies. The presence of these antibodies is used to confirm a diagnosis of rheumatoid arthritis rather than PsA.
- Anti-nuclear antibodies (ANA).These antibodies are often present in people with PsA.
Patterns of psoriatic arthritis
There are five specific patterns of inflammation that help rheumatologists tell PsA apart from other forms of inflammatory arthritis. The patterns are:
- Asymmetrical oligoarticular arthritis: four or fewer joints are affected, and feet and other large joints are usually involved. It does not necessarily occur on both sides of the body.
- Symmetrical polyarthritis: five or more joints are affected. 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, the corresponding joint on the left side is also often affected. It has symptoms similar to those of rheumatoid arthritis.
- Distal arthritis: affects the small joints closest to the nails in the fingers and toes.
- Arthritis mutilans: the most severe, destructive form of PsA. It causes a shortening of the affected fingers and toes.
- Spondyloarthritis: affects the joints of the spine. Back pain is the main symptom.
Diagnosis using the CASPAR criteria
PsA may appear if someone has psoriasis that is currently active.
Diagnosis of PsA should follow the recently developed CASPAR criteria. A diagnosis of inflammatory articular disease will often be made if a person presents with:
- 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 of the following features:
- current active psoriasis
- personal history of psoriasis, unless current psoriasis is present
- family history of psoriasis, unless current psoriasis is present or there is a personal history of psoriasis
- current or previous dactylitis, also known as "sausage fingers," where the fingers or toes are swollen
- new bone growth near a joint
- rheumatoid factor (RF) negativity
- certain nail problems, such as nail pitting and separation from the nail bed
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. On a good day, symptoms may be barely noticeable, while a flare-up of arthritis can be extremely painful.
Usually, one or more of the following symptoms appears:
- 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 straightaway. People with PsA often go undiagnosed, leaving them at risk for progressive joint damage and disability.
However, the long-term outlook for the management of PsA is good. This is especially true if it is diagnosed early and correctly, and an appropriate treatment plan is followed.
What happens after a diagnosis?
General tiredness may be a symptom of PsA.
There are many different treatment options available for PsA depending on the severity of the condition. The current goals for treatment aim to:
- reduce symptoms
- allow the joints to work as best as they can
- improve quality of life
- prevent or minimize further complications related to the disease or treatment
Recently, two groups of experts, the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) and European League Against Rheumatism (EULAR), have made recommendations to help rheumatologists decide upon the best course of action for managing PsA.
In general, their treatment recommendations are as follows:NSAIDs
Non-steroidal anti-inflammatory drugs (NSAIDs) are the first-line therapy for joints that are painful, but not yet at risk of being damaged. They work by blocking the production of prostaglandins, which signal the body's immune system to trigger an inflammatory response.
The most common over-the-counter NSAIDs are ibuprofen and naproxen sodium.Intra-articular injection
A local corticosteroid injection may be administered into affected joints to provide temporary relief from inflammation.Synthetic DMARDs
Disease-modifying antirheumatic drugs (DMARDs) may be introduced in addition to NSAIDs if needed to help to slow disease progression. They are often prescribed to people who are diagnosed in the early stages of PsA.
A new DMARD, called apremilast (Otezla), may also be prescribed. It works by blocking an enzyme that manages immune and inflammatory processes.Biologic DMARDs
Finally, a special subclass of DMARDs called tumor necrosis factor (TNF) inhibitors are typically offered if the patient does not respond effectively to other DMARDs.
TNF inhibitors work by blocking a specific protein, which is produced by immune cells that 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) and ixekizumab (Taltz) target a different protein.
Psoriatic arthritis is a progressive disease. If left untreated, it will lead to loss of function in the affected joints. Although there is no cure for PsA at present, early diagnosis and targeted treatment plans may slow, or even halt its progress.