Thyroid cancer and autoimmune connective tissue disorders

There are substantial data confirming the association between autoimmune disorders, including connective tissue diseases (CTDs), and an increased risk of thyroid malignancy. CTDs and thyroid cancer may co-exist as 2 separate diseases because of their relatively high incidence rates in the population. They can arise from each other due to the increased risk of thyroid cancer in patients with idiopathic inflammatory myositis, rheumatoid arthritis, systemic sclerosis, primary Sjögren's syndrome, and systemic lupus erythematosus. Moreover, in some scarce cases, CTDs may act as the paraneoplastic syndromes of thyroid cancer. The presence of CTDs may impact the diagnostic process, especially distorting the results of imaging tests or falsely indicating the increase of thyroglobulin or calcitonin. Finally, TSH suppression is a crucial element of the treatment of differentiated thyroid cancer, which may decrease bone mineral density and increase the risk of osteoporosis by accelerating bone turnover and shortening the bone remodeling cycle. The aim of this review is to emphasise the vital aspects of this interrelationship. The authors discuss this phenomenon aiming at the explanation of possible linking mechanisms. The impact of selected CTDs on thyroid cancer management is presented, as well as the possible effects of cancer therapy on skeletal health.