Features - Psoriatic Arthritis

The Facts

About 3% of the population is afflicted with the chronic skin disease known as psoriasis. Seven percent of these people also suffer from inflammation, pain or disability in the joints, or arthritis. When this is the case, they have psoriatic arthritis, a joint disease caused by psoriasis.

Psoriasis typically appears when people are in their 20s, 30s, or early 40s, and is equally common in men and women. People with black skin are very rarely affected. If joint problems develop, they first appear some months or years after the first skin symptoms in 75% of sufferers. About 15% of people with psoriatic arthritis get skin and joint symptoms at about the same time, while in the remaining 10%, it's the arthritis that appears first. About a quarter of psoriasis sufferers have changes in the toenails or fingernails; these people are most likely to develop symptoms of arthritis.

Causes

Psoriasis and psoriatic arthritis are inflammatory disorders of the seronegative type. That means that a certain marker - rheumatoid factor - can't be found in blood tests. Nevertheless, psoriasis belongs to the same basic class of diseases as rheumatoid arthritis, which is a seropositive disease.

While not conclusively proven, it seems almost certain that psoriatic disease is autoimmune in nature. The process is not really understood, but in these diseases the body's immune system mistakenly attacks human tissue. Most experts believe this event is probably triggered by an infection. Each new infection prompts the body to create new types of immune cells - it is not known which infections could be promoting the growth of the rogue immune cells that cause the skin and joint symptoms of psoriasis and psoriatic arthritis.

Infection alone probably isn't enough of a trigger in most cases. Some people are clearly genetically predisposed to these diseases. While psoriatic arthritis sometimes appears in children with no family history of the disease, the number of sufferers whose relatives have also been afflicted is too large to be explained by coincidence.

Symptoms and Complications

Joint inflammation in psoriatic arthritis can appear almost anywhere on the body, but the parts most likely to be affected are the fingers. Few people, however, are completely free of symptoms elsewhere in the body, and the wrists, knees and ankles are also likely targets.

The most common pattern of inflammation is the asymmetrical type. Basically, this term is used to distinguish psoriatic arthritis from rheumatoid arthritis, in which inflammation in one joint is often mirrored on the other side of the body. Asymmetrical arthritis affects joints in an apparently random fashion. Someone might have pain in the left shoulder and right knee, for example. On the other hand, it may be that the left shoulder and left knee are affected. There's no set pattern. Even so, about 25% of people with psoriatic arthritis have symmetrical inflammation.

Most people will have arthritis in their fingers and sometimes the toes, which may cause swelling of the digits into a sausage shape. This 'fattening' is usually concentrated around the knuckle joints, and is different from club fingers (fattening of the last phalange - segment - around the nail), which can be a sign of lung disease.

Most people with psoriatic arthritis do not have back pain. Those who do suffer back pain usually find it's worse at night and in the morning, and eases with activity during the day.

In very severe psoriatic arthritis, the shape of the joint and the surrounding bone and flesh can be profoundly altered. When severe arthritis causes disfiguration it's called arthritis mutilans. Rheumatoid arthritis is more likely than psoriatic arthritis to cause such severe damage.

Psoriatic arthritis tends to rise and fall in severity. As a rule, the remissions (symptom-free periods) are more complete than in rheumatoid arthritis; the arthritis may disappear totally during these periods. In some people, joint pain tends to rise and fall with the degree of skin inflammation; in others, the two processes seem to occur entirely independent of one another.

A common complication of psoriatic arthritis is tendinitis. Achilles tendinitis and tennis elbow, which can also affect the wrist, are two forms of tendinitis likely to occur in psoriasis. Bursitis (inflammation of a bursa, a fluid-filled sac found in a variety of tissues where friction would otherwise occur, such as the knee) is also a possibility.

Making the Diagnosis

Normally, it's fairly easy to diagnose psoriatic arthritis, because the skin symptoms of psoriasis (present or past) are clear indicators. Pitting of the fingernails is an almost certain sign that joint pain is caused by psoriatic arthritis and not some other form of arthritis.

The first step in diagnosing any arthritic disease is to X-ray the joints to see what changes are taking place. Next, a doctor may do a blood test for rheumatoid factor to eliminate the possibility of rheumatoid arthritis. Tests of fluid in the joints can also rule out gout, which may have arthritic symptoms very similar to psoriatic arthritis. This process of elimination is necessary because there's no test that confirms a diagnosis of psoriasis or psoriatic arthritis. That's why diagnosis of psoriatic arthritis is usually based on the characteristic presence of both skin and joint symptoms.

Treatment and Prevention

The drugs used to treat joint inflammation in psoriatic arthritis are similar to those used for rheumatoid arthritis.

Most people are started on acetylsalicylic acid (ASA)* or another non-steroidal anti-inflammatory drug (NSAID) such as ibuprofen or naproxen. These drugs are sometimes given with another drug to protect the stomach lining from the NSAID. Some newer NSAIDs, such as celecoxib may also be used. For many people, using these medications is enough to control pain and inflammation. Some people may be able to take a "drug holiday" during periods of remission.

For people with severe arthritis, and sometimes those with severe skin symptoms, the doctor may choose to use a "second-line" agent right away. These drugs affect immune processes, and often stop joint damage that wasn't responding to NSAIDs. Also used in rheumatoid arthritis, they are collectively called disease-modifying anti-rheumatic drugs (DMARDs). Intramuscular gold and sulfasalazine are two common types.

Recent studies suggest the immunosuppressive drug methotrexate may be most effective for severe psoriatic arthritis, but it carries a risk of serious side effects and requires regular monitoring.

Corticosteroids in tablet (e.g., prednisone) or injection form can also be used to control inflammation. Corticosteroid injections are injected directly into the affected joints and can help relieve severe symptoms of both arthritis and tendinitis. There are long-term effects with corticosteroids that require regular monitoring.

Many doctors favour the technique known as PUVA, in which ultraviolet (type A) light is directed on the affected skin and joints after a drug is given that increases the light sensitivity of the skin. This technique may help both skin symptoms and arthritis.

Various types of splints can be used to ease the load on affected joints and keep them aligned. Many people find these extremely helpful. In cases of irreparable joint damage, surgery can substitute artificial joints - these are improving all the time.

Exercise and strength training is usually beneficial for arthritis, but it is possible to overdo it. A doctor should be consulted about appropriate exercise programs.

*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For more information on brand names, speak with your doctor or pharmacist.


For more information on psoriatic arthritis see "All About Psoriatic Arthritis"

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Page created: 22 April 2005