About 1% to 3% of the Canadian population suffers from the chronic skin condition called psoriasis. This condition is more common among Caucasian people than among those of African descent.10% to 30% of Canadians with psoriasis will also suffer from inflammation, pain, or disability in the joints. When this is the case, they have a condition called psoriatic arthritis (PsA), a joint disease related to psoriasis.
Psoriatic arthritis typically appears when people are between the ages of 20 and 50, and it is equally common in men and women, and can occur at any age. Most people with psoriatic arthritis develop joint problems some months or years after the first skin symptoms appear. But in about 15% of the cases, the arthritis appears before the psoriasis. Over 80% of psoriasis sufferers notice changes in the toenails or fingernails.
Psoriatic arthritis is part of a type of arthritis called spondylopathies, a category of arthritis that also includes ankylosing spondylitis and reactive spondylitis. These diseases tend to be asymmetrical (both sides of the body are not affected equally). Spondylopathies also affect the spine in characteristic ways.
Psoriasis and psoriatic arthritis are inflammatory conditions of the seronegative type. That means that blood autoantibodies (a type of antibody made by the immune system, which attacks a person's own cells and tissues) which are found in other autoimmune diseases are usually not found. Nevertheless, psoriasis belongs to the same basic class of diseases as rheumatoid arthritis, which is usually a seropositive disease.
Researchers don't know exactly what causes psoriatic arthritis, but they believe it is autoimmune in nature. In these conditions the body's immune system mistakenly attacks its own tissue. Most experts believe this is probably triggered by an infection or changes in the environment, though the exact mechanism as to how and why this occurs is still not known.
Genetics and a family history of psoriasis and psoriatic arthritis play a role in the condition. 40% of people with psoriasis have a first-degree relative with the same disease. Despite the strong genetic role, psoriatic arthritis sometimes appears in children with no family history of the disease. About 30% of people with psoriasis develop psoriatic arthritis as well. This prevalence is higher in patients who also have AIDS.
Symptoms and Complications
Symptoms of psoriatic arthritis involve both skin and joint symptoms.
Skin symptoms include:
- scaly and silvery skin on the scalp, elbows, knees, or lower back that itch or burn
- fingernails or toenails that lift away from the skin or that are pitted with small holes (the nails can look similar to nails infected with the common nail fungus)
For more detailed information about skin symptoms, see the condition article on psoriasis.
Joint symptoms of psoriatic arthritis include pain, swelling, redness, and stiffness. About half of patients with psoriatic arthritis have morning stiffness, lasting more than 30 minutes, that is alleviated with physical activity. Inflammation can occur in almost any joint but typically affects the joints of the fingers and toes, which may cause the fingers to swell and become sausage-shaped. Pain and swelling is also common where tendons and ligaments attach to bone (i.e., at the elbow or back of the heel) called enthesitis. Large joints are less commonly affected.
The patterns of joint involvement in psoriatic arthritis include:
- asymmetric with few joints involved
- symmetric rheumatoid-like pattern
- involvement of only the distal joints (finger and toe joints near the nails), which is very characteristic of psoriatic arthritis and uncommon in other conditions
- enthesitis (inflammation of the tendons and ligaments that attach to bone), which is common in psoriatic arthritis and can be very disabling; when severe, it can cause dactylitis
- dactylitis (the finger or toe looks sausage-like due to joint and tendon swelling), which is very characteristic of spondylopathies and more common in psoriasis
- back and sacroiliac joint predominantly involved
- a very rare joint-mutilating form
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.
Most people with psoriatic arthritis do not have back pain, but if they do have inflammation in the spine, usually find that it is 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 tissue can change greatly. 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 inflammation tends to rise and fall in severity. The remissions (symptom-free periods) tend to be more complete than in rheumatoid arthritis; the arthritis may totally disappear during these periods. In some people, joint pain tends to rise and fall with the degree of skin inflammation; in others, the two symptoms seem to occur entirely independent of one another.
Making the Diagnosis
A doctor is able to diagnose psoriatic arthritis and eliminate other possible conditions using your medical history, a physical exam, X-rays, or tracking your symptoms over time. Often, the skin symptoms of psoriasis (present or past) are clear indicators, though occasionally these plaques are hidden on the scalp or in other non-obvious areas. Pitting of the fingernails is one sign that joint pain is probably caused by psoriatic arthritis and not some other form of arthritis.
The first step is to take an X-ray of the joints to see what changes are taking place. Next, a doctor may do blood tests and other evaluations to look for other possible causes. 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 history and the characteristic presence of both skin and joint symptoms.
Blood tests are not helpful in diagnosis, but in 40% of cases the erythrocyte sedimentation rate (a measure of inflammation) is elevated and can be used to help determine how the disease is progressing.
Treatment and Prevention
Currently, there is no cure for psoriatic arthritis, but treatment can relieve pain, reduce swelling, and improve skin symptoms. The medications used to treat joint inflammation in psoriatic arthritis are similar to those used for rheumatoid arthritis.
Most people are started on a nonsteroidal anti-inflammatory drug (NSAID) such as ibuprofen* or naproxen. In some cases, these medications are given with another medication to protect the stomach lining from the NSAID. For many people, these medications will control pain and inflammation but they will not stop the joint damage that can occur in psoriatic arthritis. Occasionally, they cause a flare-up in skin symptoms.
Local treatment of skin lesions with corticosteroid creams, phototherapy, and other skin treatments is very important.
Medications may be necessary to control symptoms and attempt to slow or stop joint damage. All medications have their own risks and side effects. You should discuss the benefits and risks of each medication with your doctor. Rheumatologists are doctors that specialize in the diagnosis and treatment of arthritis and other diseases that affect the joints, muscles, and bones. They have the most expert experience with medications that are used to treat psoriatic arthritis.
For many people with psoriatic arthritis, medications called disease-modifying antirheumatic drugs (DMARDs) are recommended. These medications affect the immune system, and can help slow down joint damage. Methotrexate is most often used.
Apremilast is a medication which blocks the activity of an enzyme in the body called phosphodiesterase 4. It is thought to work by decreasing inflammation.
Some people use a medication in the group called biologics or biologic response modifiers. These include agents like adalimumab, etanercept, golimumab, and infliximab, secukinumab, and ustekinumab. These medications help relieve the symptoms of psoriatic arthritis, improve physical function, and can help slow the progression of joint damage. There are significant risks of very serious side effects associated with biologics.
Corticosteroids in tablet (e.g., prednisone) or injection (e.g., trimacinolone) 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 serious side effects and risks with long-term use of oral corticosteroids that require careful consideration before use and regular monitoring.
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 damaged joints with artificial joints – these are improving all the time.
Exercise and strength training is usually beneficial for people with arthritis to reduce pain and increase their range of movement. A doctor should be consulted about appropriate exercise programs. People with this condition must also protect their joints. Through stretching, exercise and the use of devices to simplify tasks, daily chores will cause less stress on joints and the body in general.
For skin symptoms, some people may try therapy known as PUVA, in which ultraviolet (type A) light is directed on the affected skin after a medication is given that increases the light sensitivity of the skin. Topical medications (such as creams, ointments, and gels) applied directly to the skin can help with the skin symptoms.
For more information about the treatment of skin symptoms, see the psoriasis condition article.