hello, my mother (59 years old) has pain in his left arm for the last 2 months. She reports that the pain is on the lateral upper third arm, not the shoulder . When she raises her left arm the pain increases and precludes her from making another move for a moment. She took analgesics, muscle relaxants and physical therapy and has been no relief. No history of trauma, her work does not require any kind of effort that has caused the pain. What could it be? Does she need some kind of exams like MRI?