Hashimoto's thyroiditis classification

On the basis of the etiology, Hashimoto’s thyroiditis can be classified as primary or secondary types. Rarely, Hashimoto’s thyroiditis can be categorized under the polyglandular syndromes.

Hashimoto’s thyroiditis (HT) can be classified on the basis of the etiology to the primary and secondary types as follows:^[1]

Primary HT is the most common form of thyroiditis and comprises the cases that do not currently have identifiable causes. Primary HT encompasses a spectrum of the following main types:

• Classic form
• Fibrous variant
• IgG4-related variant
• Juvenile form
• Hashitoxicosis

Two forms of painless thyroiditis, sporadic and postpartum thyroiditis were considered the form of Hashimoto’s thyroiditis. These are now regarded as different from Hashimoto’s thyroiditis.

Secondary HT is of more recent description. It includes the forms where an etiologic agent can be clearly identified. It is more commonly iatrogenic and induced by the administration of:

• Immunomodulatory drugs (e.g, interferon-alpha)
• Monoclonal antibodies that block CTLA-4
• Cancer vaccines

In rare cases, Hashimoto’s thyroiditis may be associated with other endocrine disorders caused by the immune system. On the basis of the involvement of other endocrine disease involvements, Hashimoto’s thyroiditis may be classified under the polyglandular autoimmune syndromes. ^[2]

• Type 2 polyglandular autoimmune syndrome (PGA II):
  • Hashimoto’s thyroiditis/hypothyroidism
  • Adrenal insufficiency
  • Type 1 diabetes
• Type 1 polyglandular autoimmune syndrome (PGA I):
  • Hashimoto’s disease/hypothyroidism
  • Adrenal insufficiency
  • Fungal infections of the mouth and nails
  • Hypoparathyroidism

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