Similar to RA, psoriatic arthritis is a form of inflammatory arthritis. It affects an estimated 520,000 persons in the US.1
Symptoms and signs of psoriatic arthritis
Major signs and symptoms of psoriatic arthritis include2:
- Joint pain, with swelling and stiffness (affecting one or more joints)
- Sausage-like swelling (called dactylitis) affecting fingers or toes
- Pain in the vicinity of the feet and ankles: in some cases, tendinitis in the Achilles tendon or plantar fasciitis affecting the sole of the foot.
- Symptoms that affect the nails, including pitting and a pulling away (or separation) of the nail from the underlying nail bed
- Pain in the lower back (sacrum) above the tailbone.
In many patients with psoriatic arthritis, the arthritis component (joint pain and swelling) may follow symptoms affecting the skin and nails.
Major forms of psoriatic arthritis
There are five major forms of psoriatic arthritis.2
- 1. Distal arthritis: characterized by pain and swelling mainly affecting distal interphalangeal (DIP) joints (outermost joints of the fingers), with nail involvement (pitting, pulling away from nail bed).
- 2. Spondyloarthritis: characterized by spine involvement (resembles ankylosing spondylitis). Patients will typically test positive for the HLA-B27 antigen (determined by blood tested).
- 3. Oligoarthritis: characterized by involvement of only a few joints, with asymmetrical distribution (more on one side of body than the other). In this form of psoriatic arthritis, there is a risk for joint destruction if the disease remains active.
- 4. Symmetric polyarthritis: characterized by symmetrical joint involvement (similar to RA) and typically rheumatoid factor (RF) positive. (This may be a co-occurrence of psoriatic arthritis and RA.)
- 5. Arthritis mutilans: characterized by destructive and deforming arthritis. May result in severe deformity of hands (and sometimes feet).
How is psoriatic arthritis diagnosed?
Typically diagnosis of psoriatic arthritis is made on the basis of clinical evaluation (assessment of patient symptoms and medical history), radiographic observations, and laboratory tests, such as rheumatoid factor (RF), erythrocyte sedimentation rate (ESR), antibodies including antinuclear antibodies (ANA) and anti-cyclic citrullinated peptide (anti-CCP) antibodies. If you have both inflammatory arthritis and symptoms of psoriasis, the diagnosis of psoriatic arthritis is likely. However, a patient may have both psoriasis and arthritis and not have psoriatic arthritis, but some combination of psoriasis and osteoarthritis, or RA, gout, or inflammatory bowel disease.2
Clinical assessment plays a key role in diagnosis of psoriatic arthritis. A patient with psoriatic arthritis will often complain of joint stiffness (worse in the morning) and pain. Physical examination will reveal tenderness and pain when the joint is placed under stress. Typically, joint effusion is present. About half of patients will experience joint pain in DIP and spine.2
There are no laboratory tests that can be used to diagnose psoriatic arthritis. However, certain results may be useful in the context of clinical and radiographic (x-ray) evidence. For instance, RF factor is positive in 2% to 10% of patients with psoriatic arthritis. Additionally, the presence of certain antibodies may be suggestive of psoriatic arthritis. These include ANA and anti-CCP antibodies.2
What causes psoriatic arthritis?
We do not understand the exact cause of psoriatic arthritis, but it is thought that the disease occurs due to a combination of genetic, environmental, and other factors. Genes play a significant role in the development of psoriatic arthritis. Studies have found that heredity (what genes you inherit from your family) may account for about 40% of the risk of developing psoriatic arthritis. For instance, if you have a close family member with psoriatic arthritis, you are 50% more likely to get the disease than someone without any family member with the disease.3
Other factors such as abnormalities in your immune system or exposure to certain bacteria or viruses may also play a role in increasing risk. Results from studies suggest that exposure to streptococcal infection may be linked to development of both psoriasis and psoriatic arthritis.3
How is psoriatic arthritis treated?
Psoriatic arthritis is typically treated with a variety of medications that control inflammation and other symptoms. Exercise and physical therapy may also provide relief of joint pain and stiffness.3
Many of the same medications that are used to treat RA are also used for psoriatic arthritis. Non-steroidal anti-inflammatory drugs (NSAIDs), both over-the-counter (aspirin, ibuprofen, naproxen) and prescription, are used for pain relief and control of inflammation. The selective NSAID (also called a Cox-2 inhibitor) Celebrex (celecoxib) is less likely to cause side effects, including gastrointestinal effects, than less selective NSAIDs (ibuprofen, aspirin).3
Glucocorticoids given by injection directly into affected joints may also be useful in controlling inflammation. Oral glucocorticoids are generally not used in patients with psoriatic arthritis due to the potential for exacerbation of psoriasis.3
Disease-modifying anti-rheumatic drugs (DMARDs), including methotrexate, may be useful in patients affected by swelling of joints. These drugs have been shown to be effective in slowing or preventing joint damage.3
Newer biologic treatments (also considered DMARDs), including TNF-inhibitors such as etanercept (Enbrel) or adalimumab (Humira), have been shown to be effective in controlling symptoms of psoriatic arthritis and are often used in patients who do not respond to treatment with traditional DMARDs. These agents can also be used together with DMARDs and glucocorticoids to control inflammation and prevent joint damage associated with the disease.3