What Does Fluid On Both Ankle Joints In X-ray Indicate?

My son who is 7 was complaining of sore ankles for a long time... Mentioned it to my gp and he said it was probably growing pains. I eventually got him xrayed and it showed he has fluid on both ankle joints. He is being referred toa paediatrician now... I m so afraid it s rheumatoid arthritis.... I have my suspicions also that he is coeliac... Are there other things that might be causing this apart from RA?