My daughter, age 12 has an area on her lower back which began around first of May and about the size of a dime when we noticed it, and thought it was a bruise. The area kept getting bigger and is now approx 20mm x 40mm and is not a bruise. I took her to the pediatrician who said it was a skin issue and not spinal. The area does appear to be of different texture with no hair on this spot. The color is a brownish-grayish-bluish. She has some back ache, but the pediatrician said was just coincidental. Made an appointment w/dermatologist. Just worried about what it might be.
Hi... Thank you for consulting in Chat Doctor. Skin conditions are best diagnosed only after seeing directly. I suggest you to upload photographs of the same on this website, so that I can guide you scientifically.  Hope my answer was helpful for you.  I am happy to help any time. Further clarifications and consultations on Chat Doctor are welcome. If you do not have any clarifications, you can close the discussion and rate the answer. Wish your kid good health.