The aetiology of this condition is not clear, but hypotheses include the "metaplasia theory" (squamous metaplasia of underlying thyroid disease) and "embryonic-nest theory" (squamous cells originating from remnant ultimobranchial duct or thyroglossal duct) as a result of metaplasia of papillary or follicular cells of the thyroid or from the embryonic remnants with metaplasia of follicular epithelium (thyroglobulin positive variety) [Follicular variable]. This evidence concerns the gene TG and thyroiditis.