This is why I'm confused - the only MS with a chronic bone disease connection I can find is a condition called Musculoskeletal Sarcoid,and I'm sure this isn't a recognised acronym. I suspect the inclusion of 'bone' therefore may be an error, unless someone can shed further light on it.
More likely a boo-boo on Azed's part - he freely admits to having a bit of difficulty sometimes with the scientific stuff. Look out for an apology in next month's Azed slip, if you're a subscriber.