Psoriatic arthritis (PsA) is an autoimmune disease that includes both psoriasis and a related form of arthritis. It is a form of inflammatory arthritis that causes pain, swelling and sometimes damage to any joint in the body.
Psoriatic arthritis occurs mostly in people who are suffering from psoriasis, a chronic skin disease characterized by scaly, reddish skin rashes on the elbows, knees and scalp.
A healthy immune system acts as natural defense, releasing antibodies against injury and disease, but in autoimmune diseases such as psoriatic arthritis, the body turns against its own tissues by releasing white blood cells and causing inflammation of the synovium. The synovium lines the joint capsule and produces synovial fluid for lubrication and smooth motion of the joints.
This inflammation thickens the synovium lining resulting in turgid, swollen joints. Over time the synovium invades cartilage, the covering at the end of bones in a joint, and this erosion causes the rubbing of bone on bone in a joint (Osteoarthritis). The inflammatory response weakens the joints and its surrounding structures such as muscles, ligaments and tendons occur.
Based on the location of the affected body joints and their specific symptoms, psoriatic arthritis is divided in five classes as:
- Symmetric arthritis is similar to rheumatoid arthritis and characterized by pain, swelling and stiffness in the joint, but with mild deformities. This condition usually affects the same joint on both sides of the body, hence it is called symmetric.
- Asymmetric arthritis is characterized by fluctuating pain and tenderness of joints anywhere in the body, such as knee, hip, ankle or wrist. In some cases, painful swelling of fingers or toes called dactylitis also develops. This form is generally mild and usually responds to medical therapy.
- Distal interphalangeal predominant (DIP) is a rare type of PsA and usually affects the distal joints of fingers and toes. It can be confused with osteoarthritis, due to similar symptoms, but nail changes, such as pitting, discoloration, crumbling or detachment are specific visible characteristic features of this form.
- Spondylitis is less common and is characterized by inflammation of the spinal column resulting in stiffness of the neck, lower back, sacroiliac or spinal vertebrae making movement painful and difficult.
- Arthritis mutilans is a severe, deforming and damaging condition affecting small joints of the hands and feet. Some people also experience neck or lower back pain.
The exact cause of developing psoriatic arthritis is not known. There are several factors found to be responsible for developing psoriatic arthritis such as genetic, environmental, and immune factors. In 40 percent of the cases, genes are responsible, having family history of either psoriasis or psoriatic arthritis. Some doctors also believe that environmental factors such as trauma or an infection such as strep throat may trigger the immune system into developing PsA.
PsA occurs equally in both sexes at any time, but the peak age of onset is between 30 and 55 years.
Many symptoms of PsA are common with other form of arthritis, which makes the disease difficult to diagnose. The most common symptoms are:
- Painful, swollen joints generally affecting ankle, knees, fingers, toes, and lower back
- Dactylitis, a balloon like swelling along the entire length of fingers or toes
- Enthesitis, development of pain and tenderness in the area where tendons or ligaments attach the bones and is commonly seen at the heel or bottom of the foot.
- Low back pain due to the effect on sacroiliac joint
- Nail changes including pitting, discoloration, white areas, crumbling or detachment of nails
- Stiffness of joints either in the morning or after rest
- Reduced range of motion of joints and limbs
- Conjunctivitis, redness and pain in the tissues surrounding the eyes
The diagnosis of PsA is a difficult and time-consuming process because most of its symptoms mimic other forms of arthritis such as rheumatoid arthritis, osteoarthritis, and gout. The diagnostic process starts with a physical examination by a rheumatologist, a type of doctor specialist in arthritis and musculoskeletal diseases. Physical examination includes looking for swelling and inflammation of the joints, signs of psoriasis on skin or changes in the fingernails and toenails.
For detecting changes of the bones or joints, X-rays are ordered and certain blood tests are also included for examining factors such as C-reactive protein and rheumatoid factor, indicators of inflammation.
In some cases, joint fluid is also examined for detail analysis.
There is no cure for psoriatic arthritis and the objective of treatment is to reduce pain and swelling of the joints, prevent joint damage, preserve joint function and control psoriasis of the skin.
Different classes of medications are available for managing symptoms of PsA such as NSAIDs and corticosteroids for reducing pain and swelling. Other classes such as disease-modifying anti-rheumatic drugs (DMARDs) and biological response modifiers are also frequently prescribed.
Participating in regular exercise is the best way to treat joint stiffness and promote muscle strength. Getting adequate rest also helps in reducing tiredness due to PsA. Applying heat or ice packs on joints can also help in reducing pain and swelling. Splints may also be recommended to support joints and reduce inflammation.