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Inflammatory Disorders of Thyroid Gland

April 13th, 2022

Introduction:

Inflammatory disorders of thyroid gland are a mixture of various disorders characterized by variable clinical presentations, etiologies and treatment modalities. These disorders cause the thyroid gland to be diffusely enlarged, nodular. Functionally speaking these patients may be euthyroid, hypothyroid or hyperthyroid. These patients may not suffer from pain except in cases of post viral and suppurative thyroiditis.

Inflammatory thyroiditis are often associated with certain characteristic triggering factors:

1. Parturition

2. Viral infections

3. Medications

Classification of inflammatory thyroid disorders:

This takes into account the subjective history (painful or painless), its temporal course (acute, subacute or chronic), histopathologic features (hyperplastic, lymphocytic, granulomatous, or fibrous), and the name of the physician who first described them (Graves, Hashimoto, DeQuervain, and Riedel). These parameters cause a lot of confusion when classifying this disorder.

A simple classification of inflammatory thyroiditis has been evolved. It divides the various disorders into four main groups:

1. Autoimmune

2. Amiodarone induced

3. Infectious

4. Idiopathic

Autoimmune thyroid disease:

This is the commonest of inflammatory thyroid disorders. Disorders under this group include:

a. Hashimoto’s thyroiditis (Chronic lymphocytic thyroiditis)

b. Subacute lymphocytic thyroiditis

c. Postpartum thyroiditis

d. Grave’s disease

This group of disorders is characterized by immune reaction against thyroid autoantigens. There are three serologic markers for disorders belonging to this group. They are:

1. Antibodies against thyroid globulin (the large protein on which T3 and T4are synthesized and subsequently cleaved)

2. Thyroid microsomal antigen (also known as thyroid peroxidase)

3. Thyrotropin receptor

The presence of thyroid antibodies facilitates lymphocytic infiltration of the thyroid gland which is a feature of autoimmune thyroiditis. If thyroid receptor stimulating antibody is present, it can cause hypertrophy of the gland with minimal lymphocytic infiltration. This picture is seen in Graves disease.

Autoimmunity also can induce a thyrotropin receptor antibody which blocks normal thyrotropin from activating it causes hypothyroidism without lymphocytic infiltration.

Autoimmune thyroid disease may present either with thyroiditis or as a hyperplastic disorder i.e. Graves disease. When a clear precipitating factor could be associated with this disorder then it could be used to name the subtype of the disorder i.e. (Postpartum thyroiditis, interferon induced thyroiditis) etc. Sometimes these various subtypes of autoimmune thyroiditis could be seen in the same patient.

Hashimoto’s thyroiditis: is the most common inflammatory disorder of thyroid gland. Patients present typically with goitre, nodules, with hypothyroidism. High titres of circulating thyroid antibodies is a feature of this disorder.

Histologically, the gland shows follicular degeneration with a diffuse lymphocytic infiltration. There may also be associated fibrosis. These features are identifiable in FNAC. If there is palpable cervical node associated with Hashimotos thyroiditis then FNAC of thyroid should be performed to rule out malignancy.

Subacute lymphocytic thyroiditis: This disorder comprises of three subtypes. They are Postpartum thyroiditis, silent thyroiditis and interferon induced thyroiditis. All these three subtypes have positive microsomal antibodies.

Postpartum thyroiditis: affects 5% of females. Women with positive thyroid antibodies during the first trimester of pregnancy have roughly 50% chance of developing postpartum thyroiditis. Hyperthyroidism usually develops during the first three months following delivery. It is usually mild and may last for a few months. The patient may then become euthyroid and later hypothyroid. These patients commonly have a mild to moderately enlarged thyroid gland. TSH levels may be raised. Antithyroid drugs are not indicated in these patients on the other hand steroids may have a role to play.