Pathology of thyroid 2 Dr: Salah Ahmed

Thyroiditis - inflammation of the thyroid gland, includes a group of disorders characterized by some form of thyroid inflammation and thyroid dysfunction 1- Chronic Lymphocytic (Hashimoto) Thyroiditis: - is the most common cause of hypothyroidism in areas with sufficient iodine - is characterized by gradual thyroid failure because of autoimmune destruction of the gland - common between 45 and 65 years of age and is more common in women than in men ( 10 : 1 to 20 : 1) Pathogenesis: - It is an autoimmune disease in which the immune system reacts against different thyroid antigens with progressive destruction of thyroid epithelial cells (thyrocytes), which are gradually replaced by mononuclear cell infiltration and fibrosis - sensitization of CD4+ T-helper cells to thyroid antigens (initiating event)

- thyrocytes destruction and death, by different mechanisms: 1-cytokine-mediated thyrocytes death: reaction of CD4+ T cells to thyroid antigens, producing cytokines (IFN-γ) which promote inflammation and activate macrophages - injury to the thyroid by the toxic products of inflammatory cells 2- CD8+ cytotoxic T-cell-mediated thyrocytes death: CD8+ cytotoxic T cells recognize antigens on thyrocytes and kill these cells 3- Binding of antithyroid antibodies followed by antibody-dependent cell-mediated cytotoxicity by natural killer (NK) cells - genetic predisposition: 1- it occurs with increased frequency in first-degree relatives, and unaffected family members often have circulating thyroid autoantibodies 2- Association studies have reported linkage between HLA-DR3 and HLA-DR5 alleles and Hashimoto thyroiditis, but the associations are generally weak

Morphology: - Grossly: the thyroid is usually diffusely and symmetrically enlarged -The cut surface is pale, gray-tan, firm (LN like) - Microscopic examination: 1- widespread infiltration of the parenchyma by a mononuclear cells containing small lymphocytes, plasma cells with well-developed germinal centers 2- The thyroid follicles are atrophic 3- Less commonly, the thyroid is small and atrophic as a result of more extensive fibrosis (fibrosing variant) Clinical Features: - painless enlargement of thyroid, usually with hypothyroidism manifestation - it may be preceded by transient thyrotoxicosis (disruption of thyroid follicles ("hashitoxicosis") - Lab: - TFT: T4 and T3 levels decreased with compensatory increase in TSH - the diagnosis based on histopathological examination of thyroid excisional biopsy

Symmetrical enlargement, pale or gray-tan cut surface

Mononuclear cell infiltration with germinal center

- patients with Hashimoto thyroiditis often have other autoimmune diseases and are at increased risk for the development of B-cell non-Hodgkin lymphomas 2- Subacute Granulomatous (de Quervain) Thyroiditis: - is much less common than is Hashimoto disease - most common between the ages of 30 and 50 years, more frequently in women Pathogenesis: - is believed to be caused by a viral infection or a postviral inflammatory process. - The majority of patients have a history of an upper respiratory infection just before the onset of thyroiditis Morphology: - grossly: the gland is firm, unilaterally or bilaterally enlarged

- microscopically: there is disruption of thyroid follicles, with extravasation of colloid leading to a neutrophils infiltration, which replaced over time by lymphocytes, plasma cells, and macrophages and also giant cells Clinical Features: - characterized by pain in the neck (particularly with swallowing), fever, malaise, and variable enlargement of the thyroid, hyperthyroidism manifestation - Thyroid function test: increase in T3, T4 (disruption of follicles and hormone release - The leukocyte count and ESR are elevated - The condition is typically self-limited, with most patients returning to a euthyroid state within 6 to 8 weeks.

Disruption of follicles with inflammatory cells infiltration

3- Subacute Lymphocytic Thyroiditis : - is also known as "silent" or "painless" thyroiditis - often occurs following pregnancy (postpartum thyroiditis) - It commonly affects middle-aged women Pathogenesis: The disease is most likely autoimmune in etiology, because circulating antithyroid antibodies are found in the majority of patients Morphology: - mild symmetric enlargement of thyroid - lymphocytic infiltration microscopically Clinical manifestation: - patients presented with painless neck mass or features of hyperthyroidism (secondary to thyroid tissue damage), followed by return to a euthyroid state within a few months - In a minority of affected individuals the condition eventually progresses to hypothyroidism

4- Riedel thyroiditis: - a rare disorder of unknown etiology - is characterized by extensive fibrosis involving the thyroid and contiguous neck structures. - patients presented with a hard and fixed thyroid mass clinically -The presence of circulating antithyroid antibodies in most patients suggests an autoimmune etiology 5- Palpation thyroiditis: - caused by vigorous clinical palpation of the thyroid gland, results in multifocal follicular disruption with chronic inflammatory cells infiltration and occasional giant- cell formation - the abnormalities of thyroid function are not present - usually an incidental finding in specimens resected for other reasons.

Riedel

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