Hi I have welsh cob sec D mare she is 5 coming 6, she has always been sensitive around her mane area but becomes very twitchy if you accidently touch her wither area when you are riding. She had a good month off in the autumn as I was training babies, i decided that when i bought back into work this time i would take her back to walk excercise for 3 weeks, to encourage her to stretch through her topline and encourage her to track up, amazingly we had no twitching at all, but as soon as i started short bursts of working trot as time went on the twitching reapeared. She is mainly out in the day and in at night with ad lib hay fed low down, we take part in showing classes and dressage and a small amount of jumping only about 2ft 3 as i'm not the bravest! I use a very experienced farrier that is very aware of a well balanced foot, i also use a chiropractor as and when she is needed, she has treated this mare and did work on the wither area but found only niggles rather than a huge problem, she massaged the area and encouraged me to do the same. I'm not sure what you may think, I know its difficutl without seeing the horse,but i'm pretty sure she has a trapped nerve, what do you think?
This definitely sounds like a nerve issue, your feelings may well be correct. I've learned gut feelings should be followed. She needs some in depth diagnostic work, an x-ray would tell you a great deal. It's something that is aggravated by being asked to track up, collect herself. So bending her neck sets this off. I am really wondering if she at some point damaged her neck, possibly broke it, causing a malformation of a vertebrae, that is fine as long as she doesn't try to bend her neck past a certain point. You are doing everything right as far as hoof care and chiro care but this I think, feel, is more than that will address.
Keep me apprised of how this turns out if you get her x-rayed. She has something going on and you just have to figure it out.