There are a few possibilities which need to be ruled out. The important possibilities are erythema nodosum, lichen simplex chronicus and subacute nodular migratory panniculitis. Subacute nodular migratory panniculitis mostly effects women and presents as unilateral, single, erythematous nodule or plaque on the shins. In addition, pretibial myxedema needs to be ruled out.
I would suggest a dermatologist’s/physician/s evaluation and getting biopsy skin and blood tests done to rule out these conditions.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how the young girl is doing.
i have the same thing & it is such a pain . noone knows how to handle it ,
i have tried everything .
We found something that got rid of the rash for my daughter; using a prescription ointment called Triamcinolone Acetonide Ointment 0.1% twice a day on the rash got rid of it in about a week. At the same time we bought Nike chin guard sleeves at ****'s and use them all the time so the sweaty chin guard isn't directly touching the skin. The rash never came back after this. Good luck