Author: Dr Amy Stanway MBChB, Dermatology Registrar, 2005.
Psoriatic arthritis is a painful, inflammatory condition of the joints that usually (but not always) occurs in association with psoriasis of the skin.
Up to 40% of people with psoriatic skin disease have some signs of psoriatic arthritis. It can also affect people without psoriasis.
Symptoms of psoriatic arthritis come and go but it is a lifelong condition.
Psoriatic arthritis belongs to a group of arthritic conditions called the spondyloarthropathies. Spondyloarthropathies include:
Common features of the above four conditions include:
The main contributing factors to the development of psoriatic arthritis are genetic predisposition, immune factors and the environment.
As in psoriasis of the skin, many patients with psoriatic arthritis may have a familial tendency toward the condition. However, a twin study found that arthritis was as common in dizygotic (fraternal) twins as in monzygotic (identical) twins so unknown environmental factors may also be important. First-degree relatives of patients with psoriatic arthritis have a 50-fold increased risk of developing psoriatic arthritis compared with the general population. It is unclear whether this is due to a genetic basis of psoriasis alone, or whether there is a special genetic predisposition to arthritis as well.
There is evidence to support the theory that psoriatic arthritis occurs as a result of an abnormal interaction between the immune system and the joints. People with psoriatic arthritis seem to have an overactive immune system as is evidenced by raised inflammatory markers, in particular tumour necrosis factor (TNF), and increased antibodies and T-lymphocytes (infection-fighting cells).
Presumably some environmental factor tips the balance in favour of the development of psoriatic arthritis in an individual who is genetically predisposed to the condition. As yet no reliable environmental factor has been identified.
Psoriatic arthritis causes pain and swelling of joints, and stiffness, particularly in the morning. This may result in reduced mobility and function.
Specific problems include difficulties with using the hands, standing for long periods, and walking. Many patients with psoriatic arthritis have to discontinue or change their work because of the disease. Psoriatic arthritis may result in severe damage to the joints and can be as severe as rheumatoid arthritis.
Other signs and symptoms of psoriatic arthritis include:
Systemic features associated with psoriatic arthritis include:
Psoriatic arthritis usually affects joints in an asymmetrical pattern (that is, different joints are affected on each side of the body). Approximately one third of patients will have spinal and/or sacroiliac (hip) joint involvement and two-thirds will have arthritis affecting the limb joints without spinal disease. The following are common ways in which psoriatic arthritis can present:
People with severe psoriatic arthritis have been reported to have a shorter lifespan than average.
People with psoriatic arthritis usually have some skin signs eventually.
Psoriatic arthritis develops after skin psoriasis in approximately 70% of patients. Remaining patients have either a simultaneous onset of skin and joint psoriasis, or joint symptoms precede any skin problem. The severity of the skin diseases does not predict the severity of the joint disease.
Plaque psoriasis is the most common form of skin psoriasis seen with psoriatic arthritis. Joint symptoms may flare with a flare in skin psoriasis but quite commonly the skin symptoms behave independently of joint symptoms. Most people with psoriatic arthritis have mild psoriasis.
The diagnosis of psoriatic arthritis is based on symptoms, examination of skin and joints and compatible X-ray findings.
X-ray findings that are characteristic of psoriatic arthritis include:
Other conditions with similar clinical and X-ray findings to psoriatic arthritis include:
There are no diagnostic blood tests for psoriatic arthritis but tests may be done to help confirm the diagnosis and rule out other causes.
Some treatments for joint psoriasis are also effective for skin psoriasis, so treatment plans may take both skin and joint disease into account.
Traditionally, psoriatic arthritis has been treated with the safest medication first, using more aggressive treatment only if the first failed. It is now thought that treating the condition more aggressively from the outset may limit the eventual joint damage and disability. At this time it is not known what factors predict whether a person will have progressive joint disease.
If arthritis is mild and limited to a few joints and the skin disease is not severe, the skin is treated with topical therapies or ultraviolet light and the joint disease is managed with pain relief (non-steroidal anti-inflammatory drugs, heat and ice), physical therapy, and possibly corticosteroid injections into the joint.
If arthritis involves several joints or is moderate to severe, more aggressive therapy is likely to be needed, such as:
These medications improve symptoms of pain and stiffness but none have been shown to prevent progressive joint damage and all have potential for serious side effects. Methotrexate, ciclosporin, apremilast and leflunomide have a beneficial effect on both joint and skin disease.
Biologic response modifiers are drugs made from monoclonal antibodies that target inflammatory mediators and aim to modify specific inflammatory pathways to prevent joint inflammation. Those licensed for use in psoriatic arthritis are:
Most people with psoriatic arthritis will have ongoing problems with arthritis throughout the rest of their life. Remissions are uncommon; occurring in les than 20% of patients with less than 10% of patients having a complete remission off all medication with no signs of joint damage on X-rays.
Features associated with a relatively good prognosis are:
Features associated with a poor prognosis include:
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