@louise65 I wish I could tell you mine has resolved, because it hasn't. Like you I have no idea what caused it. My gut instinct tells me it is the way I sleep. Some mornings I wake up in severe pain and others it's not too bad. I have been going to physical therapy. Some of the exercises seem to aggravate it and others I don't seem to notice it getting any worse. I'm going to see a massage therapist who focuses on neuromuscular disorders. Since the muscles in my arm seem very tight, I'm hoping that by relaxing them it will relax the tendons and therefore the area of tendon attachment will have less pulling, so maybe that will allow it to settle down. My PT tells me this won't work, but my PT hasn't helped me thus far so I'm willing to try something different.