Forearm Pain and Stiffness in a 34-Year-Old Woman

A 34-year-old woman had progressive skin tightening over her right elbow and forearm, bilateral forearm pain, difficulty extending her fingers and elbows, and elevated eosinophil count and C-reactive protein level; examination showed a linear depression along a superficial vein when the right forearm was raised. What is the diagnosis and what would you do next?