Skin disorders and thyroid diseases

Thyroid disorders have a high prevalence in medical practice; they are associated with a wide range of diseases with which they may or may not share etiological factors. One of the organs which best show this wide range of clinical signs is the skin. This review is an attempt to approach most of the dermopathies reflecting several degrees of harmfulness, coming directly or indirectly from thyroid abnormalities, as well as to update current knowledge on the relationship between the thyroid and skin. We have proposed a primary classification of skin disorders, regarding thyroid involvement, into two main groups: 1) dermopathies associated with thyroid abnormalities, mainly with autoimmune thyroid diseases, like melasma, vitiligo, Sjogren's syndrome, alopecia, idiopathic hirsutism, pre-menstrual acne, bullous diseases, connective tissue diseases, hamartoma syndrome, atopy, leprosy and DiGeorge anomaly; and 2) dermopathies depending on the nature of the thyroid disorder, in which the evolution and outcome of the skin disorder depend on the thyroidal treatment in most cases, such as trophism and skin blood flow, myxedema, alopecia, onychodystrophy, hypo- and hyperhidrosis, xanthomas, intraepidermal bullae, carotenodermia, pruritus, flushing, pyodermitis, palmoplantar keratoderma, ecchymosis, etc. In some other cases, the skin disease which developed as a consequence of the thyroid abnormality can remain unaltered despite functional treatment of the thyroid problem, such as pretibial myxedema, thyroid acropachy and some cutaneous manifestations of multiple endocrine neoplasia types 2A and 2B.