Riedel Thyroiditis
Bruce M. Wenig, MD
Key Facts
Terminology
Idiopathic fibrosing process and not per se an inflammatory (thyroiditis) thyroid disease
Etiology/Pathogenesis
Association between RT and Hashimoto thyroiditis supports autoimmune pathogenesis
Presence of thyroid dysfunction, bilateral ophthalmopathy, and thyrotropin receptor stimulating autoantibodies
RT may be part of systemic fibrosing disease (also known as inflammatory fibrosclerosis)
Recent evidence suggests RT part of IgG4-related systemic disease spectrum
Clinical Issues
Painless neck mass &/or goiter
Thyroid is enlarged, woody or stony hard on palpation and adherent or fixed to surrounding structures
Microscopic Pathology
Destruction and replacement of thyroid parenchyma by dense collagen (keloid-like)
Fibrosing process is not confined to thyroid but also involves extrathyroidal connective tissues
Vasculitis is present, primarily involving veins (phlebitis)
Remnant of thyroid follicles may be present (but may be difficult to identify)
 Virtually all of the thyroid tissue is replaced by dense keloid-like bands of fibrous tissue with an associated chronic inflammatory cell infiltrate. Colloid-filled follicles can be seen  . |
 There is keloid-like fibrosis with chronic inflammation predominantly composed of plasma cells and lymphocytes, but scattered eosinophils  are present. Note colloid-filled follicles  . |
TERMINOLOGY
Abbreviations
Riedel thyroiditis (RT)
Synonyms
Invasive fibrous thyroiditis
Ligneous thyroiditis
Definitions
Idiopathic fibrosing process
Not per se an inflammatory thyroid disease (thyroiditis) of thyroid gland
ETIOLOGY/PATHOGENESIS
Autoimmune Disease
Presence of mononuclear cells and detection of autoantibodies directed against thyroid-specific antigens favors autoimmune pathogenesis
Association between RT and Hashimoto thyroiditis furthers supports autoimmune pathogenesis
RT may evolve from antecedent Graves disease
May be associated with other autoimmune diseases including
Systemic lupus erythematosus, scleroderma, polyarteritis nodosa, multiple sclerosis
Systemic Fibrosing Disease/Igg4-Related Systemic Disease
RT may be part of systemic fibrosing disease (also known as inflammatory fibrosclerosis)
Recent evidence suggests RT part of IgG4-related systemic disease spectrum
Characterized by IgG4(+) plasma cell infiltration and fibrosis in many organs
Systemic disease may include
Retroperitoneum, mediastinum, retro-orbit, lung, sinonasal tract, parotid gland, lacrimal gland, hepatobiliary tract (sclerosing cholangitis)
RT may coexist with one or more of these other sites of involvement
Only retroperitoneal fibrosis linked to possible etiologic agent (i.e., methysergide)
CLINICAL ISSUES
Epidemiology
Incidence
Uncommon disease
Age
Primarily occurs in adults
Gender
Female > Male
Presentation
Painless neck mass &/or goiter
Pressure in anterior neck often associated with dysphagia, dyspnea, stridor
Rarely, vocal cord paralysis may occur due to recurrent laryngeal nerve involvement
Compression and encasement of internal jugular vein and carotid artery may occur
Thyroid is enlarged, woody or stony hard on palpation and adherent or fixed to surrounding structures in neck
Involvement of thyroid may be limited in extent so that 1 side is predominantly involved
Bilateral involvement of thyroid can also occur
Presence of hard and fixed thyroid mass clinically simulates a neoplastic lesion (i.e., carcinoma)
Impression of neoplasm further suspected in cases associated with cervical lymph node involvement
Clinically, patients present with stony hard goiter frequently associated with compressive symptoms
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