my daughter has a small purple line the size and thickness of the tip of a fingernail on her back. it is slightly indented and has had it for a few years now. it sometimes is painful to the tocuh or arm movement then will go away for several weeks before bothering her again. its more if a nuisance paid like a scratch or bruise and does not interefere with her active lifestyle. She is 15 and in a dance company so she is active. SHe has seen a doc in the past, ha blood taken, seen another doc, nothing resulted other than keep an eye on it for growth which it never has changed. Any idea what this could be and if I should be concerned its something serious? She would have never notived it if it had not been tender, it is that small of a mark only visible when you know what your looking for.