How Psoriasis and Psoriatic Arthritis Are Connected

About one in 20 people with psoriasis will also develop a condition called psoriatic arthritis. Arthritis is an inflammatory condition that affects the joints. Patients may experience pain, tenderness, stiffness and swelling at various joints.

Here we see the flaky skin patches typical of psoriasis forming on a patient’s hand, as well as signs of inflammation in the joints of the wrist and fingers, ankles and toes, and especially the lower spine. If left untreated, psoriatic arthritis can eventually lead to permanent joint damage.

For reasons that remain uncertain, people with psoriasis are victims of their own immune systems gone awry. Here we see a white blood cell, which would ordinarily protect the individual against foreign invaders, attacking the patient’s own skin cells. The white blood cell incorrectly identifies types of skin cells called keratinocytes as foreign. It releases chemicals known as cytokines to trigger an immune system attack on the targeted skin cells. This leads to the inflammation and abnormally rapid growth of keratinocytes that is associated with psoriasis.

The same process that causes skin cell damage may also trigger damage to joints in some people with psoriasis. Here we see circulating white blood cells passing through a blood vessel next to a joint. The mistakenly hostile white blood cells pass through the blood vessel wall, then through the synovial membrane of the joint and into the synovial fluid that bathes and lubricates the cartilage-encased bone of the joint.

Once in the synovial space, the white blood cells release inflammatory cytokines—immune system proteins that trigger the destruction of cartilage, and eventually bone. This inflammation may be experienced as stiffness, swelling, redness, and pain in the affected joint.

In this animation, at first we see the normal, rapid growth of the protective outer layers of skin cells (the epidermis). Circulating in blood vessels below, white blood cells begin to release inflammation-promoting proteins called cytokines. These compounds provoke inflammation, and cause the upper layers of skin cells to grow out of control. This results in the formation of the thick, raised, flaky, whitish-silver patches of inflamed skin that are typical of psoriasis.

By advancing the slider from left to right, it’s easy to see the progression of inflammation in the finger joints of a patient afflicted with psoriatic arthritis. As the inflammation progresses, joints become increasingly inflamed and begin to swell. You may experience experience tenderness, stiffness, and pain in the joints, and increasing difficulty using your fingers to accomplish the ordinary tasks of everyday living.