Thyroid disease in Sjögren's syndrome.

From 1960 to 2007, an important number of patients with primary Sjögren's syndrome (pSS) along with thyroid disease diagnosed by laboratory data and clinical presentation were reported. The most common thyroid disorder found was autoimmune thyroiditis and the most common hormonal pattern was subclinical hypothyroidism. The coexistence of SS and thyroiditis is frequent and suggests a common genetic or environmental factor predisposition with similar pathogenic mechanisms. pSS was ten times more frequent in patients with autoimmune thyroid disease and autoimmune thyroiditis was nine times more frequent in pSS. Therefore, SS should be studied in patients with thyroid disease and vice versa. Antigens are shared by both thyroid and salivary glands, which could be responsible for the association between both diseases. Immunogenetic studies had suggested that both diseases have a common genetic predisposition. pSS and thyroid disease patients were mostly women with positive antithyroglobulin, antiparietal cell and antithyroid peroxidase antibodies. Thyroid dysfunction is frequent in pSS patients and those prone to develop thyroid disorders are identified by thyroid-related autoantibodies or by rheumatoid factor and anti-Ro/SSA activity. Patients with pSS have an increased tendency to develop other autoimmune diseases. Hypothyroidism was the most common autoimmune disease developed in pSS patients during follow-up of 10.5 years. Lymphomas are also associated with SS and thyroiditis and a 67-fold increased risk for thyroid mucosa-associated lymphoid tissue (MALT) lymphoma and a 44-fold increased risk for parotid lymphoma is being attributed to autoimmune thyroiditis and pSS. It is suggested that immune mechanism deficiency is a causal factor for B cell lymphoma in pSS and autoimmune thyroid disease. Other studies are necessary to clarify the shared pathogenesis mechanism in SS and autoimmune thyroid disease and to understand this fascinating autoimmune association.