Infectious thyroiditis

Introduction Acute suppurative thyroiditis (AST) is a rare but potentially life-threatening infection. AST is usually bacterial in etiology, although fungal, parasitic, and mycobacterial organisms have also been documented causes. The routes of infection are predominantly hematogenous or lymphatic; however, thyroid infections may also be the result of direct spread from an adjacent deep fascial space infection, an infected thyroglossal fistula, or anterior perforation of the esophagus. Thus, infectious thyroiditis may occur either as a local infection or as part of a disseminated systemic infection. Because prognosis is dependent on prompt diagnosis and treatment, it is important to differentiate AST from the noninfectious inflammatory conditions of the thyroid and other inflammations in the neck that it may closely resemble. Pathogenesis The thyroid gland is rarely infected, and several protective factors have been postulated to explain why the gland is relatively resistant to infection. First, there is a rich blood supply to and extensive lymphatic drainage from the thyroid. Second, the high iodine content of the gland may be bactericidal; however, there are no data to show that the concentration of iodine present in the thyroid would be enough to inhibit the growth of microorganisms. Third, in addition to being surrounded by a complete fibrous capsule, the thyroid is separated from the other structures of the neck by fascial planes.