Eosinophilic fasciitis is a very rare syndrome in which muscle tissue underneath the skin, called fascia, becomes swollen and thick. Rapid swelling can occur in the hands, arms, legs, and feet.
The disease is similar in appearance to scleroderma but is not related.
The cause of eosinophilic fasciitis is unknown. Fewer than 300 cases have been reported in the past 35 years.
People with this condition have a buildup of eosinophils, a type of white blood cell, in the affected fascia and muscles. Eosinophils are related to allergic reactions, but their exact function is unknown.
The syndrome affects people of any age, but is more common in people ages 30 to 60.