I Have A Question. My Son For No Reason At

I have a question. My son for no reason at all started getting rash like bruises under the skin on his feet, ankles and calves.

We have taken him to the doctor and they have done blood work and all is test done are normal. His platlet counts our normal as well.

We had them check for leukemia as well and came back negative. We are dumbfounded.

Do you have any idea