DEAR DOCTOR K: My doctor thinks my arthritis and heart disease are connected to my psoriasis. Is this possible? I thought psoriasis was a skin condition.

DEAR READER: Psoriasis is named for an ancient Greek word meaning an itchy or scaly condition. It is classified as a skin disease, but psoriasis is the result of an immune system abnormality that can cause problems throughout the body.

With psoriasis, white blood cells of the immune system become overactive. They produce excess amounts of chemicals that trigger inflammation. The inflammation leads to abnormally rapid growth of cells in the skin’s outer layer. This causes plaques: raised, red patches covered with silvery scales on the elbows and knees – the classic sign of psoriasis.

But the effects of psoriasis are not always confined to the skin. The disease also can cause inflammation throughout the body. This probably is the reason that people with psoriasis have higher rates of various diseases that also are associated with a constant state of inflammation. These include diabetes, heart disease, high blood pressure and several types of cancer.

When psoriasis involves only the skin, it often can be treated just by medicines applied to the skin. Very mild cases of psoriasis may improve with moisturizers and some sunlight. But most people need other treatments.

Research in recent years has led to biologic agents that directly neutralize some of the body’s chemicals (called cytokines) that cause inflammation. They have proved very effective in severe psoriasis. Though they carry a risk of serious side effects, the benefits generally are greater than the risks.