**Question:** All are true about Hashimoto's thyroiditis except ?

A. Hashimoto's thyroiditis is a cause of hypothyroidism.
B. Hashimoto's thyroiditis is a cause of hyperthyroidism.
C. Hashimoto's thyroiditis is a cause of goiter formation.
D. Hashimoto's thyroiditis is a viral infection.

**Correct Answer:** B. Hashimoto's thyroiditis is a cause of hyperthyroidism.

**Core Concept:**
Hashimoto's thyroiditis is a common immune-mediated disorder that results in the destruction of thyroid follicular cells, leading to hypothyroidism. Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormones (triiodothyronine and thyroxine) due to the inflammation and damage in the thyroid gland. This results in lower than normal hormone levels in the bloodstream.

**Why the Correct Answer is Right:**
Hashimoto's thyroiditis is a cause of hypothyroidism as it results in the destruction of thyroid follicular cells. Hypothyroidism is a condition characterized by low levels of thyroid hormones in the bloodstream, which leads to a range of clinical symptoms and signs. Hypothyroidism is typically treated with thyroid hormone replacement therapy.

**Why Each Wrong Option is Incorrect:**

A. Hashimoto's thyroiditis is a cause of hypothyroidism, not hyperthyroidism. Hypothyroidism is caused by an underactive thyroid gland, while hyperthyroidism is caused by an overactive thyroid gland.

B. Hashimoto's thyroiditis is an autoimmune disorder leading to hypothyroidism, not hyperthyroidism. Hypothyroidism is the primary outcome of Hashimoto's thyroiditis, not hyperthyroidism, which is usually associated with Graves' disease.

C. Hashimoto's thyroiditis is an autoimmune disorder leading to hypothyroidism, not hyperthyroidism. Hypothyroidism is the primary outcome of Hashimoto's thyroiditis, not hyperthyroidism. In contrast, hyperthyroidism is usually associated with Graves' disease or toxic multinodular goiter.

D. Hashimoto's thyroiditis is an autoimmune disorder, not a viral infection. It is characterized by the production of antibodies against thyroid antigens, leading to inflammation and destruction of thyroid follicular cells, resulting in hypothyroidism. Viral infections typically cause acute illnesses and resolve, unlike Hashimoto's thyroiditis, which is a chronic condition.

**Clinical Pearl:**
Hashimoto's thyroiditis is an important autoimmune disorder to know about, as understanding its pathophysiology and management can help in the diagnosis and treatment of hypothyroidism. Although autoimmune thyroid disorders are more common in women, they can also affect men and are often associated with a family history of thyroid disease.