What Is Psoriatic Arthritis?
Psoriatic arthritis is a type of arthritis that develops in some people who experience the skin condition psoriasis. The skin is in a constant process of regeneration, and completely replaces itself over the course of a month. New skin cells form underneath the outer layer of older skin, which then sloughs off to expose the newer skin.
Psoriasis develops when the regeneration process occurs too quickly- the new skin cells develop faster than they should and the old skin is not shed quick enough. This causes scaly red patches of skin to form, known as plaques, which can become very sore and itchy. These psoriasis plaques are usually found in localized patches on the knees, elbows, buttocks or head but can be found anywhere on the body and can occasionally cover a wider area.
Psoriatic arthritis generally only develops in psoriasis sufferers, although this does not mean that psoriasis sufferers will automatically develop the condition, nor does it mean that those with the most severe psoriasis symptoms will develop more severe forms of psoriatic arthritis. The condition occurs in around five to ten percent of people with psoriasis. In addition, around fifteen percent of people develop psoriatic arthritis before experiencing the symptoms of psoriasis.
Different Types of Psoriatic Arthritis and Their Symptoms
There are five different types of psoriatic arthritis, and each type has its own symptoms and treatment.
Symmetric arthritis; this affects the same joints in pairs, on each side of the body; for example both knee joints will be affected. The symptoms resemble a milder form of rheumatoid arthritis, although it can occur in more severe forms and cause deformity to the joints. Symmetrical arthritis is the second most common form of psoriatic arthritis and tends to cause more severe psoriasis symptoms.
Asymmetric arthritis; this tends to affect only a few joints, generally less than five, and joints are affected individually rather than in pairs. Although any joint can be affected, it is most common on the fingers and toes, and can cause a swelling in fingers known as 'sausage digits'. Asymmetrical arthritis is one of the most common forms of psoriatic arthritis, and is milder and less progressive than other types.
Digital Interphalangeal Predominant (DIP) arthritis; this affects the last joint in the toes and fingers, and can be mistaken for osteoarthritis.
Arthritis mutilans; this is a rare form of psoriatic arthritis, affecting fewer than 5% of sufferers, but can be severe. It can destroy cartilage and bone tissue, and can cause deformity to the hands, feet or spine. It generally occurs in flare ups and subsequent remissions, which are reflected in the symptoms of psoriasis.
Spondylitis; this is an inflammation of the spinal joints and discs, and can be very severe, resulting in spinal deformities if not treated. It can also affect the joints and ligaments in the arms and legs. The predominant symptoms include stiffness in the back and neck joints, tenderness and inflammation.
People with psoriatic arthritis may develop more than one of these types and can show symptoms of several at any one time, which can make diagnosis of one single type more difficult. There are also other types of arthritis that sufferers of psoriasis are at risk of developing; these are gout, which causes sudden inflammation in the toes, feet or hands, rheumatoid arthritis, osteoarthritis and Reiter's Syndrome, which causes arthritis as well as inflammation of the urethra and eyes.
Other Psoriatic Arthritis Symptoms
In addition to the above symptoms, there are several more which can indicate the presence of the condition;
- Swelling, throbbing, redness and stiffness in the affected joints, particularly first thing in the morning or after a period of rest
- Reduced range of movement in the affected joints of digits
- Swelling to the fingers or toes, as the joints and connective tissues become inflamed
- General tiredness
- Changes in finger and toe nails; nails may become thicker or become 'pitted' in appearance
These symptoms can be mild or more severe and can flare up and die down in a similar manner to the symptoms of psoriasis, and the two conditions can even mirror each other at times. Psoriatic arthritis occurs more frequently in the finger and toe joints, particularly the end joints, but can affect any joint in the body.
Although there is no cure for psoriatic arthritis, there are many treatments available to relieve the symptoms and avoid further damage to the joints.