I have the same thing, bone pain. That was one of my first symptoms to show its ugly little self to me 6 years ago. I have Triple Negative ET. I had constant bone pain but also constant pain throughout my body. When I spoke to my now Hem/Onco about this I would explain the pain as bone deep. He told me it is the MPN that does cause it. When the Besremi is working I don't have nearly the pain that I use to. I still have bad days when I can barely move because of the bone pain but it isn't every day. I have my good days and my bad days.