I have been one of those who has had really debilitating pain on Letrozole which I started taking in August 2018 - joints, muscles, tendons - the works. I keep injuring myself without knowing how. So far, my left shoulder has escaped any effects. It has also caused osteo-arthritis in my hands; something that would have probably happened 20 years down the track but I'm certainly not ready for it yet. I had bursitis in my right shoulder last year and no idea what I did to cause it. I was surprised when, at last visit, my oncologist said that seeing how badly it affected me, he didn't think I would last the first year on Letrozole. But I'm too pig-headed for my own good, I guess. For me, and I'm not saying this should be the case for anyone else, if I was going to take something and suffer side effects then I wanted to be taking the one with the best results for my sub-type (ILC) and that is Letrozole. So as long as I could endure it, that was my thinking. I am glad to say that a combination of regular pain-killers, some not so regular pain management, and a couple of goes on prednisolone when it got too bad, has seen me out the other side of the worst of the side effects. I still ache and hobble after sitting or sleeping. I am hyper-prone to injury and the arthritis in my hands has not gone away. But the constant high level pain has mostly subsided. I still need pain relief on some days but not every day.
But I do want to stress to anyone reading this who may have AIs in their future, it does not affect everyone this way. I was one of the unlucky ones.