A rare case of Riedel's thyroiditis, 6 years after retroperitoneal fibrosis: two diseases with one pathogenesis?

We describe a 70-yr-old female patient in whom both a retroperitoneal fibrosis and 6 years later a Riedel's thyroiditis were diagnosed. Both diseases belong to the group of fibrotic diseases called "multifocal fibrosis". Retroperitoneal fibrosis is now known to be an auto-allergic reaction to lipid components of the atherosclerotic process in the abdominal aorta, resulting in a fibrotic reaction around it. We hypothesize that similarly Riedel's thyroiditis is in fact a periarteritis of the carotid artery, resulting in cervical fibrosis, secondarily involving the thyroid. This hypothesis would account for the occurrence of these two rare diseases in one patient.