Hi
I have coeliac disease too, which is another auto immune disease. It manifests itself in many different ways, causing diarrhoea, constipation, fatigue, mouth ulcers, headaches, etc, different symptoms for different people, so sometimes hard for doctors to diagnose. There is a specific coeliac blood test that you can request, and if that is positive then a endoscopy of the GI tract is a definitive diagnosis. It is important to keep eating gluten until a biopsy is done to avoid a false negative result.
I think that there are other bowel diseases that are auto immune also...is Crohns?? I don't know about Anti Synthetase causing bowel problems, unless the passage of food through the gut is slower because of muscle weakness perhaps?
Be interesting to know what you find out!
Alison