Psoriasis is a common, chronic condition characterized by the presence of red, scaly patches of skin, most commonly found on the elbows, knees, and scalp. Psoriatic arthritis is a condition of joint inflammation, pain, and stiffness that sometimes occurs along with skin psoriasis.
Psoriasis and psoriatic arthritis are thought to be autoimmune conditions, in which the immune system mistakenly attacks the body’s own cells, causing inflammation and other problems. In particular, immune-system cells called T cells and various cytokines (proteins that act as messengers telling immune-system cells what to do) have been shown to play a role in both the start and continuation of inflammatory activity. In psoriasis, the immune system attack causes skin cells to grow and move to the surface of the skin very rapidly. These cells then accumulate and form lesions. In psoriatic arthritis, the immune system also attacks tissues in and around the joints. If left untreated, this attack can lead to joint damage.
We do not know the cause of either psoriasis or psoriatic arthritis, but genetic factors appear to play an important role. Researchers often investigate whether a condition may have a genetic component by looking at identical twins and determining how often both twins have the condition. In 70% of twins affected by psoriasis, both twins have the condition, suggesting that genes do play a role. A person whose parent, sibling, or child develops psoriatic arthritis is 50 times more likely to develop it than someone with no family history of the condition. This likelihood increases if the family member affected is the person’s father. Research has linked psoriatic arthritis with certain genes, but the presence of genes alone does not determine whether a person will develop the condition. It’s thought that genes set the stage, and environmental factors trigger the disordered immune system response.
A number of environmental factors have been implicated. Infection with streptococcal bacteria, such as strep throat, can lead to the development of a type of psoriasis called guttate psoriasis (more on this type below). Some people with human immunodeficiency virus (HIV) also have psoriasis or psoriatic arthritis, and HIV infection can worsen existing disease. In some cases, psoriasis or psoriatic arthritis develops after physical trauma to the skin or joint. This is referred to as the “Koebner phenomenon” in the case of psoriasis and the “deep Koebner phenomenon” in psoriatic arthritis.
Who gets psoriatic arthritis?
An estimated 5 million Americans are affected by psoriasis. It isn’t known how many people with psoriasis develop psoriatic arthritis; estimates from different studies range from 5% to 30%. Overall, men and women are affected with equal frequency.
Psoriasis and psoriatic arthritis can affect people of any age, but psoriatic arthritis usually begins between the ages of 30 and 60. Skin symptoms appear before joint symptoms in 70% of cases. In 15% of cases, skin symptoms appear after the onset of arthritis, and in the remaining 15%, skin and joint symptoms appear at about the same time.
People whose psoriatic arthritis tends to be more severe include those with extensive areas of skin affected, a strong family history of psoriasis, certain genes associated with psoriasis, and arthritis that affects many joints or causes joint damage. Being a woman or having received a diagnosis of psoriasis or psoriatic arthritis before age 20 also adds to the likelihood of a poor prognosis. People with the above risk factors may require more aggressive treatment earlier on in the course of their condition.
What are the signs and symptoms?
Psoriatic arthritis can affect the skin, the joints, and many other parts of the body.
Skin. The most common skin symptom is the development of plaques, or raised, red patches of skin covered by silvery scales. This type is commonly referred to as plaque psoriasis. Less common forms include guttate psoriasis, characterized by small, round, red lesions; pustular psoriasis, in which raised and scaling patches include pus-filled bumps; and inverse psoriasis, in which deep red patches of inflammation and scaling form in body folds such as the underarms. A rare but severe form of psoriasis is erythrodermic psoriasis, which involves large areas of intense redness and shedding of skin. Affected patches of skin may be itchy or painful. Any area of the body can be affected, but symptoms are commonly seen on the elbows, knees, scalp, palms, and soles of the feet; on the torso; behind the ears; in and around the navel; and in the crease between the buttock and the thigh. Skin symptoms may come or go, and periods of increased symptoms are known as flares.
Joints. Strictly defined, the term arthritis refers to joint (“arthr-”) inflammation (“-itis”). However, it is used more loosely to refer to more than 100 musculoskeletal diseases. These conditions may be divided into two major categories: “mechanical” and “inflammatory.” Osteoarthritis is the main form of mechanical arthritis, with pain and joint damage caused predominantly, but not exclusively, by physical stresses on the joint. Rheumatoid arthritis (RA) is the most common form of inflammatory arthritis, with pain and joint damage caused by inflammation. Psoriatic arthritis is a form of inflammatory arthritis. Joint inflammation leads not only to pain but also to stiffness, swelling, and redness. Inflamed joints can feel hot to the touch.
Any joint may be affected by psoriatic arthritis, but doctors have identified several common patterns of joint involvement. These categories can help doctors reach a diagnosis and decide which treatments to try first. An individual case of psoriatic arthritis can fall into more than one of the following categories, or move from one to another over time.
- In monoarticular or asymmetrical oligoarticular arthritis, just one joint or a few joints are affected. This form is typically milder than others and is more common, accounting for 30% to 50% of cases.
- Symmetrical polyarticular arthritis affects pairs of joints on both sides of the body, such as both knees or both elbows. This form is also common, affecting 30% to 50% of people with psoriatic arthritis, and it is clinically similar to RA.
- Axial arthritis, sometimes called psoriatic spondylitis, affects joints in the spine. It may also affect the sacroiliac joints, where the spine meets the pelvis. An estimated 30% to 35% of people with psoriatic arthritis have axial arthritis.
- Distal interphalangeal prominent arthritis affects the joints at the ends of the fingers and toes. It occurs in about one-fourth of people with psoriatic arthritis and is nearly always associated with changes in the fingernails or toenails.
- Arthritis mutilans is characterized by damage to the small bones of the fingers. It is a severe form of psoriatic arthritis thought to affect about 5% of people with the condition.
Fingers and toes. Psoriasis and psoriatic arthritis can cause changes to the fingernails and toenails, such as pitting, separation from the nail bed, or a yellow-orange discoloration (doctors refer to this as the “oil drop” sign). Fingers and toes may also develop dactylitis, also called “sausage digit,” a condition of inflammation and swelling of the entire digit.
Tendons and ligaments. Psoriatic arthritis can cause enthesitis, or inflammation where the tendons and ligaments attach to bone. Enthesitis commonly affects the plantar fascia in the foot, the Achilles tendon near the ankle, and tendons near the knee, shoulder, and pelvis.
Other parts of the body. Rarely, psoriatic arthritis can lead to inflammation in other parts of the body, including the eyes, lungs, and heart.
How is psoriatic arthritis diagnosed?
There are no specific criteria for the diagnosis of psoriatic arthritis. Rather, doctors make the diagnosis after considering the person’s symptoms and ordering certain tests. In a person with psoriasis, joint symptoms aren’t necessarily due to psoriatic arthritis — it’s possible to have psoriasis and RA, osteoarthritis (OA), gout, or another type of arthritis or arthritis-related condition. To make a diagnosis of psoriatic arthritis, the doctor must rule other conditions out.
If a person has signs and symptoms of inflammatory arthritis, the doctor needs to consider RA, especially if several joints are affected on both sides of the body. The doctor will test the blood for rheumatoid factor, an antibody that is often found in people with RA but not usually in people with psoriatic arthritis. If rheumatoid factor is present at a significant level, the person is likely to have both psoriasis and RA.
Gout is also a possibility, particularly if just one joint or a few joints are affected. Gout is caused by a buildup in the blood of uric acid, a condition called hyperuricemia. The built-up acid can form crystals that become lodged in joints, causing severe pain and inflammation. Hyperuricemia can result from increased cell turnover, which is the underlying problem in psoriasis. To check for gout, the doctor draws by needle a sample of joint fluid, which is examined under a microscope for the presence of uric acid crystals.
When the distal interphalangeal joints of the fingers are affected, the doctor must consider gout as well as OA. OA doesn’t necessarily cause a lot of inflammation, so if the joint is red and swollen, psoriatic arthritis is more likely.
As noted earlier, joint symptoms can appear before skin symptoms in an estimated 15% of people with psoriatic arthritis. In these cases, it can be difficult for the doctor to make a diagnosis. Whenever a person’s symptoms suggest psoriatic arthritis as a possibility, the doctor should look for signs of psoriasis in the nails, scalp, and navel, behind the ears, and in the crease between the buttock and thigh.
A doctor may order x-rays to aid in the diagnosis. On x-rays, a joint with psoriatic arthritis usually shows a unique blend of bone destruction and new bone formation, and this and other signs can point the doctor in the right direction. There are no laboratory tests that can specifically point to psoriatic arthritis, but laboratory tests that measure levels of inflammation may be used to track how active the condition is.
How is psoriatic arthritis treated?
There is no cure for psoriatic arthritis, but a number of different treatments can help to reduce pain and improve quality of life.
Medicines. To treat joint symptoms, doctors generally begin with nonsteroidal anti-inflammatory drugs (NSAIDs). Some NSAIDs, such as ibuprofen (brand names Advil, Motrin IB) and naproxen sodium (Aleve), are available over the counter; others are available only by prescription. These drugs can help to relieve pain and swelling, but they don’t address the underlying activity of psoriatic arthritis.
People with aggressive and potentially destructive psoriatic arthritis should start on disease-modifying antirheumatic drugs (DMARDs) as early as possible. As the name suggests, DMARDs act to interrupt the disease process and can therefore help to prevent joint damage. Several different types of DMARDs are used:
- Methotrexate (Rheumatrex, Trexall) can help to treat both skin and joint symptoms of psoriatic arthritis. It is generally the first choice of DMARD, given that doctors have observed it to be effective and that people who take it tend to tolerate it well. Methotrexate can cause liver problems, among other side effects, so doctors give periodic liver function tests to people who take it.
- If methotrexate isn’t effective, a doctor may prescribe a biologic drug in addition to or instead of methotrexate. Anti-TNF drugs are the specific type of biologic typically used. These drugs block an immune system protein called tumor necrosis factor–alpha. The anti-TNF drugs adalimumab (Humira), etanercept (Enbrel), golimumab (Simponi), and infliximab (Remicade) have all received Food and Drug Administration (FDA) approval for use in psoriatic arthritis. Enbrel, Humira, and Simponi are injected under the skin, and Remicade is given by intravenous infusion. Because biologic drugs powerfully suppress the immune system, the side effect of most concern is infection.
- Sulfasalazine (Azulfidine) may help with joint symptoms, but it has no significant impact on the activity of skin disease.
- The immunosuppressant drug cyclosporine (Neoral, Sandimmune) may be effective for both skin and joint disease, but it may lead to high blood pressure or kidney problems. People who take cyclosporine may need to be monitored for these conditions.
- Antimalarial drugs such as chloroquine (Aralen) have been used to treat psoriatic arthritis, but doctors don’t often prescribe them because they are associated with flares of skin symptoms in some people.
To treat skin symptoms, synthetic forms of vitamin A called retinoids, such as acitretin (Soriatane) and isotretinoin (Claravis and others), may be taken orally or used as a topical gel or cream. Topical corticosteroids are also used to treat skin symptoms. In addition, corticosteroid injections or low-dose oral corticosteroids may be used as a “bridge therapy” at the start of treatment with a DMARD. It can take several weeks for a DMARD to have an effect, and a corticosteroid can help to control joint and skin symptoms in the meantime. One potential concern with oral corticosteroids is that tapering the dose can provoke a flare of skin symptoms.
Exercise and physical therapy. Physical measures are also helpful. Strength-training exercises can help to strengthen the muscles surrounding an affected joint, allowing them to better support the joint. Stretching exercises can help to preserve or improve joints’ range of motion, and low-impact aerobic exercise, such as walking, bicycling, or swimming, can help to improve cardiovascular health, control weight, and improve mood and sleep. Joints should be rested during flares of inflammatory activity, and wearing splints can help to keep joints at rest. A physical and occupational therapist can help you find ways to protect painful joints and maintain function.
Light therapy. Artificial sources of ultraviolet light can help to relieve skin symptoms. Sometimes ultraviolet A light is used with a type of drug called a psoralen, which makes the skin more sensitive to light.
Top 10 self-management tips
Although psoriatic arthritis is a chronic condition, there are many things you can do to manage your symptoms and stay active.
- Know your condition. Learn as much as you can about psoriatic arthritis so that you can understand how the condition progresses, factors that make symptoms better or worse, and the pros and cons of available treatments. The more you know, the better able you will be to work with your health-care providers in making treatment decisions, as well as to identify flares of disease activity or adverse effects of medicines. The resources listed here are good places to seek further information.
- Stick to your treatment regimen. For many people, receiving a diagnosis of a chronic illness such as arthritis involves some grieving — it can be difficult to come to terms with loss of function, the need to take medicines on a daily basis, and other changes the condition can bring. One possible response to these emotions is denial, which some people express by not taking the medicines prescribed to them. Drug side effects and costs may also make you want to stop treatment. However, the result of discontinuing treatment is likely to be worsened symptoms and further loss of function.
- Communicate with your health-care providers. Keep your primary-care physician, rheumatologist, and other members of your health-care team up to speed on any symptoms, medicine side effects, or loss of function you are experiencing, as well as any other concerns that arise. This will allow your health-care team to help you solve problems well before they become major issues.
- Establish a regular program of exercise. Work with your doctor or a physical therapist to develop an exercise plan that helps you build or maintain strength, flexibility, function, and endurance and that includes activities you enjoy.
- Aim to reach and maintain a healthy weight. Although your weight has no direct impact upon the activity of psoriatic arthritis, excess weight can place extra stress on inflamed and painful joints. In addition to getting regular exercise, eat a diet that focuses on vegetables, fruits, whole grains, and lean meats, fish, and dairy products in moderate portions. Consider consulting a registered dietitian for help in planning a healthful diet.
- Monitor and address cardiovascular risk factors. People with chronic inflammatory arthritis are at increased risk for cardiovascular disease. While treating the underlying inflammation is important, so is addressing any abnormalities in blood pressure, blood sugar, and cholesterol levels. Your primary-care physician or rheumatologist will be able to assist you in achieving this goal.
- Treat and control skin symptoms. Seek a referral to a dermatologist to treat your skin symptoms. In addition to taking the oral medicines or topical treatments prescribed to you, take good care of your skin. Keep it moist with creams or ointments recommended by your dermatologist, and avoid products and habits (such as scratching) that irritate the skin.
- See your doctor to evaluate flares of joint symptoms. If your arthritis affects more than one joint but one joint is “acting up” more than others, talk to your primary-care physician or rheumatologist. An unusually active joint may be infected, or you may be experiencing a flare of gout.
- If you work, discuss your condition with your employer. Educate your employer about psoriatic arthritis and how it affects (and does not affect) your ability to do your job. You and your employer can then work together to modify your workstation and responsibilities as necessary and as feasible and practical. This will maximize your ability to maintain productive employment.
- Seek support. Educate family and friends about your psoriatic arthritis so they understand how it affects you and know how they can help. Consider participating in a support group, where you can share your experiences and learn from others dealing with similar issues. To find a support group, consult the resources listed on page here.