When Psoriasis Gets Under Your Skin and in Your Joints

Author:

Karen Barrow

Medically Reviewed On: May 11, 2005

More than 4.5 million adults suffer from psoriasis, a chronic condition that causes red, flaky patches of thickened skin. This uncontrollable overgrowth of skin cells can appear on the scalp, hands, feet and genitalia. But the lesions most commonly appear on the elbows, knees and lower back, which might give a hint as to why almost one third of psoriasis sufferers also have a compounding disease, psoriatic arthritis, which affects the joints and can be crippling.

Psoriatic arthritis, however, can be effectively treated in most patients if it is recognized early enough. Alan Menter, MD, chief of dermatology at Baylor Medical Center in Dallas, Texas outlines this potentially disabling disease and the treatments available for it.

What is psoriatic arthritis?
Psoriatic arthritis is an inflammatory joint disease that is almost always associated with a skin disease called psoriasis. There are five different subtypes of the joint disease: anything from just a few swollen fingers and toes to more severe involvement of large joints to very disabling involvement where the hands and feet and the spine get pretty inflamed and chronically destroyed, actually. [It is mainly associated with a decrease in the range of motion, more so than pain.] So, it's a whole range from very minor disease to very severe disease, which can be disabling in about 20 percent of patients.

What causes psoriatic arthritis?
As with a lot of other diseases, there's a genetic component, but there's an environmental component as well, possibly illnesses, infections, stress. There are eight different genes associated with the skin disease, and some of those are also associated with the joint disease.

Psoriasis an immune-mediated disease, whereby T cells, [normal immune cells] are increased in number. As these cells circulate into the skin and the joints, they produce a chemical by the name of TNFα. This chemical leads to the destruction of the skin and the destruction of the joints. But the exact trigger factors of psoriasis, outside of the genetic factors, all remain to be elucidated.

Does skin psoriasis always lead to psoriatic arthritis?
Psoriasis usually occurs five to ten years before the joint disease develops. One out of three patients with the skin disease will develop the joint disease. And the severity of the skin disease does not correlate with the development of psoriatic arthritis. In other words, you can get just a few small patches of skin disease but devastating joint disease, or you can get devastating skin disease with no joint disease. However, psoriatic arthritis is going to present as skin disease in nine out of ten cases before it ever occurs in the joints.