These conditions can happen after long term illness such as RA or can be triggered by emotional or physical trauma. They are incompletely understood and frustrating as, by definition, they are associated with negative test results and normal X rays and scans.
These are very real conditions and need sensitive management with a combination of medication, graded exercises and sometimes talking therapies such as CBT. It is important to recognise these conditions and realise that they are real and need real treatments whilst their actual cause remains obscure. They are more common than people recognise and can cause lots of personal and family upset