Exploring the "thyroid-skin connection": concepts, questions, and clinical relevance.
The "thyroid-skin connection" has become a hot frontier in dermatoendocrinology. In this context, the pituitary hormone that controls thyroid hormone production, thyrotropin (TSH), caught the attention of skin researchers only after it was reported that the receptor for TSH (TSH-R) is transcribed and translated by selected cultured human skin cell populations and in normal human scalp skin in situ, introducing skin as a nonconventional, peripheral target organ for regulation by TSH. In this issue, Cianfarani et al. present corroborating evidence and raise the old question of whether intracutaneous TSH-R stimulation by autoantibodies contributes to the skin changes seen in autoimmune thyroid disease. This provides a good opportunity to define the questions to be addressed when exploring the thyroid-skin connection.