Sometimes symptoms of Crohn's disease can develop outside the digestive tract in other parts of the body (systemic symptoms), including the eyes, liver, blood, and bones. These systemic symptoms suggest that the immune system is involved in Crohn's disease. Systemic symptoms can include:1
Skin conditions, which happen in about 10% to 20% of people who have Crohn's disease. Examples include mouth ulcers and pyoderma gangrenosum, which is an eruption of painful, spreading ulcers that usually occur on the legs. The ulcers may be blue in the center with red edges. Mouth ulcers are more common than pyoderma gangrenosum, which is fairly rare.
Low bone mass. This happens in 3% to 30% of people who have Crohn's disease. The risk is greater for people who take corticosteroid medicines. It can lead to osteoporosis and, later, broken bones. More than half of people who take steroids for the long term get osteoporosis.