Eosinophilic fasciitis is a very rare syndrome in which muscle tissue under the skin, called fascia, becomes swollen and thick. The hands, arms, legs, and feet can swell quickly. The disease may look similar to scleroderma but is not related. The cause of eosinophilic fasciitis is unknown. In people with this condition, white blood cells called eosinophils, build up in the muscles and tissues. Eosinophils are linked to allergic reactions. The syndrome is more common in people ages 30 to 60. Symptoms can include: bone pain or tenderness, carpal tunnel syndrome, muscle weakness, tenderness and swelling of the arms, legs and sometimes the joints, and thickened skin that looks puckered. In most cases, the condition goes away within 3 to 5 years. However, symptoms may last longer or come back.