Distinguishing autoimmune thyroid disease is difficult in early stages. Both may have low TSH initially. Graves' disease is overactive thyroid,while Hashimoto's may have low TSH due to Hashitoxicosis. Thyroid abs & radioactive iodine uptake assist dx
Determining the pathophysiology of autoimmune thyroid disease can be challenging, especially in the early stages.
Both disorders may initially present with low TSH. In Grave’s disease, an overactive thyroid and overabundance of thyroid hormones signal the pituitary to produce less TSH (Taylor 2018). However, in early Hashimoto’s, the TSH may be low due to thyrotoxicosis or “Hashitoxicosis.” In this case, damage to thyroid cells causes a release of preformed thyroid hormone, which signals the pituitary to produce less TSH (Shahbaz 2018).
Additional studies, including thyroid antibody testing, can help evaluate the clinical picture (Pagana 2021, Ross 2016, Frohlich 2017):
- Hashimoto's disease is characterized by elevated anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) antibodies
- Graves' disease is characterized by elevated thyroid-stimulating immunoglobulins (TSI) and TSH receptor antibodies (TRAb) but may also have elevated anti-Tg antibodies in some individuals.
- Radioactive iodine uptake will often be high in Graves’ disease but low or normal in Hashitoxicosis
References
Fröhlich, Eleonore, and Richard Wahl. “Thyroid Autoimmunity: Role of Anti-thyroid Antibodies in Thyroid and Extra-Thyroidal Diseases.” Frontiers in immunology vol. 8 521. 9 May. 2017, doi:10.3389/fimmu.2017.00521
Iqbal, Aqsa. and Anis Rehman. “Thyroid Uptake and Scan.” StatPearls, StatPearls Publishing, 3 October 2022.
Pagana, Kathleen Deska, et al. Mosby's Diagnostic and Laboratory Test Reference. 15th ed., Mosby, 2021.
Ross, Douglas S et al. “2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis.” Thyroid : official journal of the American Thyroid Association vol. 26,10 (2016): 1343-1421. doi:10.1089/thy.2016.0229
Shahbaz, Amir et al. “Prolonged Duration of Hashitoxicosis in a Patient with Hashimoto's Thyroiditis: A Case Report and Review of Literature.” Cureus vol. 10,6 e2804. 14 Jun. 2018, doi:10.7759/cureus.2804
Taylor, Peter N et al. “Global epidemiology of hyperthyroidism and hypothyroidism.” Nature reviews. Endocrinology vol. 14,5 (2018): 301-316. doi:10.1038/nrendo.2018.18