From the Guidelines
Hashimoto's thyroiditis and Graves' disease are two distinct autoimmune conditions that affect the thyroid gland, and it is rare for a patient to progress directly from hypothyroidism caused by Hashimoto's to hyperthyroidism caused by Graves' disease. However, some patients with Hashimoto's can experience temporary periods of hyperthyroidism, known as "Hashitoxicosis," during the inflammatory destruction of thyroid tissue, which releases stored thyroid hormones into the bloodstream 1. Additionally, about 15-20% of patients with autoimmune thyroid disease may have antibodies associated with both conditions simultaneously. The underlying mechanism involves different antibodies: Hashimoto's features antibodies that attack thyroid tissue (anti-TPO and anti-thyroglobulin), while Graves' disease involves antibodies (TSI) that stimulate the thyroid to overproduce hormones. Though rare, some patients can transition between these conditions over time due to shifts in their autoimmune response.
Key Points to Consider
- The most common cause of hypothyroidism in the United States is chronic autoimmune (Hashimoto) thyroiditis, while common causes of hyperthyroidism include Graves disease, Hashimoto thyroiditis, and functional thyroid nodules 1.
- Risk factors for an elevated TSH level include female sex, advancing age, white race, type 1 diabetes, Down syndrome, family history of thyroid disease, goiter, previous hyperthyroidism, and external-beam radiation in the head and neck area 1.
- The serum TSH test is the primary screening test for thyroid dysfunction, and multiple tests should be done over a 3- to 6-month interval to confirm or rule out abnormal findings 1.
- Regular monitoring of thyroid function through blood tests is important for patients with autoimmune thyroid disorders to detect any changes in thyroid status that might require adjustment in treatment approach.
Treatment Approaches
- The principal treatment for hypothyroidism is oral T4 monotherapy (levothyroxine sodium) 1.
- Hyperthyroidism is treated with antithyroid medications (such as methimazole) or nonreversible thyroid ablation therapy (for example, radioactive iodine or surgery) 1.
From the Research
Hypothyroidism and Hashimoto's Thyroiditis
- Hypothyroidism is a condition where the thyroid gland is underactive, leading to a decrease in the production of thyroid hormones 2.
- Hashimoto's thyroiditis is an autoimmune disease that is the leading cause of hypothyroidism in iodine-sufficient areas 3.
- It is characterized by lymphocytic infiltration and follicular destruction, leading to gradual atrophy and fibrosis of the thyroid tissue 3.
Relationship between Hashimoto's Thyroiditis and Hyperthyroidism
- There is no direct evidence to suggest that hypothyroidism from Hashimoto's thyroiditis can progress to hyperthyroidism from Graves' disease [no relevant studies].
- However, Hashimoto's thyroiditis can present with thyrotoxicosis, which is a condition where stored thyroid hormones are released into the circulation from destroyed thyroid follicles 4.
- This is different from hyperthyroidism caused by Graves' disease, which is an autoimmune disease that stimulates the thyroid gland to produce excess thyroid hormones.
Clinical Presentation and Treatment
- The clinical presentation of Hashimoto's thyroiditis can vary, including thyrotoxicosis, euthyroidism, and hypothyroidism 4.
- Treatment for hypothyroidism caused by Hashimoto's thyroiditis typically involves thyroid hormone replacement therapy with synthetic levothyroxine 2, 3, 4.
- The management of thyrotoxicosis in Hashimoto's thyroiditis is based on symptoms control, usually with β-blockers 4.