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Hashimoto thyroiditis, also termed chronic autoimmune thyroiditis or chronic lymphocytic thyroiditis, is an autoimmune disorder characterized by immune-mediated destruction of thyroid follicular cells. Autoantibodies directed against thyroid peroxidase and thyroglobulin, along with T-cell–driven cytotoxicity, contribute to progressive glandular inflammation, fibrosis, and loss of thyroid function. Hashimoto thyroiditis represents the most common cause of hypothyroidism in iodine-sufficient regions. Clinical expression is heterogeneous, ranging from euthyroidism to subclinical or overt hypothyroidism, with some individuals experiencing a transient hyperthyroid phase related to follicular cell destruction. Disease progression is influenced by genetic susceptibility, environmental factors, and immune dysregulation. Structural thyroid changes, including goiter or atrophy, may be present, and the condition is frequently associated with other autoimmune disorders, underscoring its systemic implications. This course strengthens clinician competence in the comprehensive evaluation and management of Hashimoto thyroiditis across the disease spectrum. Participants refine skills in interpreting thyroid function tests, antibody profiles, and imaging findings to support accurate diagnosis and monitoring. Evidence-based approaches to levothyroxine initiation, dose adjustment, and long-term follow-up are reviewed, alongside emerging data on nutritional considerations and patient-centered symptom management. Emphasis is placed on recognizing comorbid autoimmune conditions and addressing reproductive, cardiovascular, and metabolic implications. Collaboration within an interprofessional healthcare team—including clinicians, nurses, pharmacists, dietitians, and behavioral health specialists—enhances patient outcomes by promoting coordinated care, consistent education, adherence support, and shared decision-making. Effective communication across disciplines supports individualized treatment planning and improves long-term disease control and quality of life. Objectives: Identify coexisting autoimmune diseases, cardiovascular risk factors, pregnancy-related risks, and complications requiring additional evaluation or referral. Differentiate autoimmune-mediated thyroid destruction from central hypothyroidism, nonthyroidal illness, and transient thyroiditis to avoid inappropriate treatment.

Identify coexisting autoimmune diseases, cardiovascular risk factors, pregnancy-related risks, and complications requiring additional evaluation or referral. Differentiate autoimmune-mediated thyroid destruction from central hypothyroidism, nonthyroidal illness, and transient thyroiditis to avoid inappropriate treatment. Implement standardized follow-up and monitoring protocols to ensure safe dose adjustment and prevent iatrogenic hyperthyroidism or undertreatment. Develop clear, bidirectional communication strategies with the interprofessional healthcare team to coordinate diagnosis, treatment initiation, monitoring, referral, and patient education in the management of Hashimoto thyroiditis. Access free multiple choice questions on this topic.

Hashimoto thyroiditis is an autoimmune disease characterized by destruction of thyroid follicular cells via cell- and antibody-mediated mechanisms. This disease is also known as chronic autoimmune thyroiditis and chronic lymphocytic thyroiditis. Hashimoto thyroiditis is the most common cause of hypothyroidism in developed countries.[1] The pathophysiology of this disease involves the formation of antithyroid antibodies and T cell activation that target thyroid tissue, leading to progressive fibrosis. Together with Graves disease, this condition comes in the category of autoimmune thyroid disorders.[2] This condition was initially described by the Japanese physician Haruto Hashimoto in 1912 as "struma lymphomatosa" after he observed enlarged thyroids with lymphocytic infiltration.[3] Women are more commonly affected. The female-to-male ratio is at least 7:1 to 10:1.[4] The incidence of Hashimoto thyroiditis increases with age, with most cases occurring between ages 45 and 55.[5] The incidence tends to be higher in countries with lower iodine deficiency prevalence.[2] Hashimoto thyroiditis can occur alone or as part of autoimmune polyglandular syndrome.[6] Some individuals with Graves disease might transform into Hashimoto thyroiditis and vice versa. This could indicate a common pathogenesis for these disorders, but different clinical presentations.[7][8][9][10]

The underlying etiology of Hashimoto thyroiditis is still not fully understood, but the cause is thought to be a combination of genetic and environmental factors. Genetic Factors Hashimoto thyroiditis has been shown to have a strong familial predisposition, with disease clustering in families, including some members developing Graves disease. A Danish study reported 50% concordance for Hashimoto thyroiditis and 80% concordance for thyroid antibody positivity among monozygotic twins. Several genes, including those encoded by the human leukocyte antigen (HLA) complex, immune regulatory genes (CD40, FoxP3, CD25, CTLA-4, and PTPN22), and thyroid-specific genes (thyroid-stimulating hormone [TSH] receptor and thyroglobulin), are linked to the development of Hashimoto thyroiditis.[11][12] Furthermore, Hashimoto thyroiditis is more common in individuals with Turner syndrome and Down syndrome.[13][14] Environmental Factors Since only 50% of monozygotic twins in a Danish study showed concordance for Hashimoto thyroiditis, environmental factors appear to play an essential role in its development.[15] Hygiene hypothesis As with many allergic and autoimmune conditions, individuals living in more hygienic environments with reduced exposure to microbial agents appear to have a higher incidence of Hashimoto thyroiditis.[16] Iodine status Mild iodine deficiency has been associated with a lower prevalence of Hashimoto thyroiditis, whereas chronic exposure to excess iodine intake has been associated with a higher prevalence of Hashimoto thyroiditis. This is partly because highly iodinated thyroglobulin creates a more immunogenic intrathyroid environment.[17][18][19] Significant iodine deficiency also increases thyroid autoimmunity.[20][19][17] Selenium status

Mild iodine deficiency has been associated with a lower prevalence of Hashimoto thyroiditis, whereas chronic exposure to excess iodine intake has been associated with a higher prevalence of Hashimoto thyroiditis. This is partly because highly iodinated thyroglobulin creates a more immunogenic intrathyroid environment.[17][18][19] Significant iodine deficiency also increases thyroid autoimmunity.[20][19][17] Selenium status Selenoproteins are essential for thyroid function and protection.[21][22] The important thyroidal selenoproteins are the iodothyronine deiodinases, glutathione peroxidases, and thioredoxin reductases. These enzymes are involved in thyroid hormone metabolism, maintenance of cellular metabolism, regulation of the redox state, and protection against oxidative damage from reactive oxygen species.[23][24] Deficiency in this mineral has been associated with a higher risk of Hashimoto thyroiditis. A systematic review and meta-analysis published in 2024 found that thyroid antibody levels decreased with selenium supplementation, independent of underlying selenium deficiency and thyroid hormone replacement. Thyroid-stimulating hormone levels also reduce with selenium supplementation, independent of thyroid hormone replacement. The certainty of this evidence was moderate.[25] Iron status Thyroid peroxidase is an enzyme that contains heme (iron). Hence, iron deficiency can impair thyroid function and increase thyroid autoimmunity.[17][26] Individuals with Hashimoto thyroiditis are at higher risk for comorbid conditions like celiac disease and autoimmune gastritis, which are often associated with iron deficiency.[27][28] Women of reproductive age are also at high risk for developing iron deficiency due to blood loss during menstruation.[29] Vitamin D status Vitamin D has been established as an important immunomodulator.[30] Individuals with vitamin D deficiency have higher thyroid antibody levels, possibly contributing to the development and progression of Hashimoto thyroiditis.[31][32] The association between vitamin D receptor polymorphisms and thyroid autoimmunity has yielded conflicting results.[33] Role of gut microbiome

Vitamin D has been established as an important immunomodulator.[30] Individuals with vitamin D deficiency have higher thyroid antibody levels, possibly contributing to the development and progression of Hashimoto thyroiditis.[31][32] The association between vitamin D receptor polymorphisms and thyroid autoimmunity has yielded conflicting results.[33] Role of gut microbiome The gut microbiota regulates the immune system and contributes significantly to thyroid hormone metabolism. Hence, alterations in the gut microbiome can increase the risk of thyroid autoimmunity.[34][35][36][37] Whether alterations in the gut microbiome occur before or after the development of Hashimoto thyroiditis is unclear. A cross-sectional study of euthyroid individuals found no robust differences in gut microbiome alpha- or beta-diversity between individuals with or without thyroid peroxidase antibodies.[38]

Hashimoto thyroiditis is the most common cause of hypothyroidism in the United States (US) and in those areas of the world where dietary iodine intake is adequate.[39] A systematic review and meta-analysis, including studies from multiple countries, found the global prevalence of Hashimoto thyroiditis to be 7.5%, with a higher prevalence of 11.4% in low- and middle-income areas.[40] Additionally, the prevalence in women was 4 times that in men.[40] Approximately 10% of the US population has thyroid antibody positivity. Results from various studies have also shown that the prevalence of thyroid antibody positivity in the general population ranges from 5% to 20%.[41][42][43][44][45] Thyroid peroxidase antibodies are present in 5% to 14% of pregnant individuals, whereas thyroglobulin antibodies are present in 3% to 18% of pregnant individuals.[46]

The presence of lymphocytic infiltration and thyroid follicular fibrosis is characteristic of Hashimoto thyroiditis. Both cellular (T cell-mediated) and humoral (B cell-mediated) immune responses play essential roles in the pathogenesis of this disorder.[47] Role of B Cells Individuals with Hashimoto thyroiditis have the following polyclonal antibodies specific to thyroid antigens: Thyroid peroxidase antibody: The most common antibody in Hashimoto thyroiditis. These are found in over 90% of individuals with Hashimoto thyroiditis.[48][49] Thyroglobulin antibody: Present in 50% to 80% of individuals with Hashimoto thyroiditis.[48][50] TSH receptor antibody, TSHR Ab: Various types have been identified. These can be stimulating, blocking, or neutral.[51][52][53] The vast majority of TSHR Abs in Hashimoto thyroiditis are blocking. Rarely, individuals with Hashimoto thyroiditis may have TSHR-stimulating antibodies, which can also cause thyroid eye disease. This might also explain why few individuals with Hashimoto thyroiditis switch to Graves disease.[54][55] Role of T Cells CD8+ T cells are a central part of the immune dysfunction underlying the pathogenesis of Hashimoto thyroiditis. These cytotoxic cells infiltrate thyroid tissue, causing inflammation and the destruction of follicular cells.[56] CD4+ T cells activate other immune cells, particularly macrophages and B cells, thereby promoting the production of autoantibodies.[47] Different subsets of CD4+ T cells, including Th1, Th2, Th17, and Tregs (regulatory T cells), have various functions, and their imbalance contributes to the pathogenesis of Hashimoto thyroiditis.[57] Th1 cells are upregulated in Hashimoto thyroiditis, promoting inflammation in thyroid tissue. Tregs are critical in promoting immune tolerance and avoiding excessive immune responses. Tregs are downregulated in Hashimoto thyroiditis.[58]

The most commonly described histopathological abnormality in Hashimoto thyroiditis is lymphocytic infiltration and destruction of follicular cells (see Image. Hashimoto Thyroiditis).[59][60] Immune cells commonly include lymphocytes and plasma cells, while others include macrophages and, occasionally, giant cells.[60] Fibrotic tissue is typically noted. Lymphoid follicles containing Hurtle cells and large follicular-derived cells, also called Askanazy cells, with eosinophilic granules, are often present.[61][62] Histopathological variants of Hashimoto thyroiditis have been described, including: Atrophic and fibrotic variants [63] Riedel thyroiditis [64][65] Immunoglobulin G4-related thyroiditis [66][67][68]

Individuals with Hashimoto thyroiditis have varying presentations. Hyperthyroidism or Hashitoxicosis A small proportion of individuals with Hashimoto thyroiditis present with hyperthyroidism. This condition is known as Hashitoxicosis. This likely occurs because follicular cells are destroyed, thereby causing leakage of stored thyroid hormones into the bloodstream. This hyperthyroidism is usually transient. This presentation is similar to subacute thyroiditis. These individuals could be at risk of developing permanent hypothyroidism.[69][70][71] A small percentage of individuals with Hashimoto thyroiditis might switch to Graves disease and present with hyperthyroidism after being hypothyroid for years before the switch.[72][73][74] Euthyroid State Most individuals with Hashimoto thyroiditis are euthyroid with normal thyroid function tests. About 20% to 30% of individuals with Hashimoto thyroiditis develop hypothyroidism.[75] Subclinical Hypothyroidism These individuals have elevated TSH, usually less than 10 mIU/L, with normal T4 and T3 levels.[76] Overt Hypothyroidism These individuals present with symptoms of hypothyroidism, a TSH of more than 10 mIU/L, or low T4 and rarely T3 levels. Usual symptoms include fatigue, unintentional weight gain, cold intolerance, constipation, changes in menstrual cycles (typically heavy menstruation), hair loss, brittle nails, depression, confusion, and brain fog. Individuals may notice periorbital puffiness, ankle swelling, voice changes, muscle aches/weakness, neuropathy, and joint pain.[77][78][79] Thyroiditis Thyroiditis can manifest as a painless or painful condition. Thyroid inflammation results in transient thyrotoxicosis, a rare manifestation of Hashimoto thyroiditis. Most cases are painless. A few may be accompanied by throat pain. These cases are resolved within a few months.[80] Rare reports on prolonged or recurrent painful thyroiditis have been published, with some individuals even needing thyroidectomy.[81][82][83] Reproductive Effects in Women Women may be found to have Hashimoto thyroiditis if they experience recurrent miscarriages or an inability to conceive. Hashimoto thyroiditis can also impair assisted conception.[84][85][86] The effects of hypothyroidism on fertility and pregnancy are not discussed in this article. Postpartum Thyroiditis

Reproductive Effects in Women Women may be found to have Hashimoto thyroiditis if they experience recurrent miscarriages or an inability to conceive. Hashimoto thyroiditis can also impair assisted conception.[84][85][86] The effects of hypothyroidism on fertility and pregnancy are not discussed in this article. Postpartum Thyroiditis Postpartum thyroiditis is a condition in postpartum women that usually develops around 6 months after childbirth, but it can occur anytime within a year in the postpartum phase. This condition is mostly seen in women who have underlying Hashimoto thyroiditis, most likely due to the rebound of the immune response after pregnancy, which can result in an exaggerated autoimmune response destroying thyroid follicular cells. Postpartum thyroiditis is usually transient, but a few women might develop permanent hypothyroidism.[87][88] Thyroid Nodularity Ongoing inflammation in the thyroid gland in Hashimoto thyroiditis leads to the development of thyroid nodules. Around 20% to 30% of individuals with Hashimoto thyroiditis have thyroid nodules, and the incidence increases with age.[87] Some individuals may have compressive neck symptoms (eg, dysphagia, dyspnea, dysphonia, chronic cough, and pressure) due to the development of thyromegaly with or without thyroid nodularity. Eye Involvement Up to 6% of individuals with Hashimoto thyroiditis can be affected by thyroid eye disease.[54] About 15% of individuals with Hashimoto thyroiditis have TSHR Ab. Most of these are the blocking type. A small proportion of individuals may have TSHR-stimulating antibodies, which can lead to ocular involvement.[54][89][90]

Laboratory Studies The following laboratory studies may be used for diagnostic evaluation of thyroid function and identification of comorbid conditions: Thyroid function tests: TSH and T4 levels should be tested to assess thyroid function. Thyroid antibodies: Thyroid peroxidase antibody is positive in over 90% of cases, whereas thyroglobulin antibody is positive in 50% to 80% of cases. Elevated thyroid antibodies correlated with disease activity.[91] Individuals with thyroid antibody positivity have a high probability of developing overt hypothyroidism, whereas individuals with negative antibody levels are more likely to present with subclinical hypothyroidism. A positive family history is also more likely when thyroid antibodies are elevated. These individuals are also more likely to have a larger thyroid gland size.[92][50] If a patient presents with thyroid eye disease, TSH receptor antibody levels should be assessed. Iron studies: Serum iron levels should be checked in individuals with clinical symptoms of iron deficiency and gastrointestinal symptoms, given the higher prevalence of celiac disease and atrophic gastritis in individuals with Hashimoto thyroiditis. Vitamin D level: Vitamin D status should be assessed, given the increased incidence of vitamin D deficiency in individuals with thyroid disorders.[93] Other Biochemical Abnormalities: A fasting lipid panel may reveal elevated LDL cholesterol, and, rarely, hypothyroidism can cause unexplained elevations in creatine kinase levels. Imaging Studies: A thyroid ultrasound can be performed if thyroid enlargement or nodularity is noted on physical examination or if the patient has compressive symptoms.

Current clinical guidelines emphasize disease management rather than prevention or cure. Thyroid Hormone Replacement The mainstay of treatment for hypothyroidism that develops due to Hashimoto thyroiditis is thyroid hormone replacement. The drug of choice is titrated levothyroxine sodium administered orally, which has a half-life of 7 days and can be given daily. Levothyroxine sodium, which is best taken early in the morning on an empty stomach for optimum absorption, should not be taken with iron or calcium supplements, aluminum hydroxide, or proton pump inhibitors to avoid suboptimal absorption. The standard dosage is 1.4-1.8 µg/kg/day, but this may vary among patients. Individuals younger than 60 should be commenced on a standard full dose if TSH is greater than 20 mIU/L; however, lower doses should be used in patients with cardiovascular diseases and older adults. In patients aged 60 or older, the recommended starting dose is 25 µg/day, with reevaluation in 6 to 8 weeks. In contrast, during pregnancy, the thyroxine dose needs to be increased by 30%. In patients with short-bowel syndrome and malabsorption, increased doses of levothyroxine are required to maintain a euthyroid state.[94] Treatment in Euthyroid Women Some experts will recommend initiating levothyroxine in women with a TSH greater than 2.5 with or without a history of pregnancy loss and in women using assisted reproductive measures.[76] The new guidelines from the American Society of Reproductive Medicine recommend against the treatment of women with TSH levels less than 4 with levothyroxine due to a lack of evidence for reduced miscarriages, improved fertility, reduced adverse obstetric outcomes, or improved developmental outcomes in children.[95] These decisions should be individualized on a case-by-case basis. Role of Selenium Supplementation

Some experts will recommend initiating levothyroxine in women with a TSH greater than 2.5 with or without a history of pregnancy loss and in women using assisted reproductive measures.[76] The new guidelines from the American Society of Reproductive Medicine recommend against the treatment of women with TSH levels less than 4 with levothyroxine due to a lack of evidence for reduced miscarriages, improved fertility, reduced adverse obstetric outcomes, or improved developmental outcomes in children.[95] These decisions should be individualized on a case-by-case basis. Role of Selenium Supplementation Recent systematic reviews and meta-analyses have shown modest benefits for managing Hashimoto thyroiditis in individuals without thyroid hormone replacement, with improved thyroid function parameters and reduced thyroid antibodies.[25][96] More research is needed to establish clear benefits. Selenium supplementation at 50 to 100 µg daily may be beneficial and safe, particularly in areas with selenium deficiency.[97] A study of 412 individuals with hypothyroidism due to Hashimoto thyroiditis who received selenium supplementation (200 µg/day) showed improvements in quality-of-life parameters.[98] Iron Deficiency Treatment Each unit increase in iron level has been shown to reduce the risk of Hashimoto thyroiditis by 43% in women of reproductive age.[99] Vitamin D Deficiency Treatment

Recent systematic reviews and meta-analyses have shown modest benefits for managing Hashimoto thyroiditis in individuals without thyroid hormone replacement, with improved thyroid function parameters and reduced thyroid antibodies.[25][96] More research is needed to establish clear benefits. Selenium supplementation at 50 to 100 µg daily may be beneficial and safe, particularly in areas with selenium deficiency.[97] A study of 412 individuals with hypothyroidism due to Hashimoto thyroiditis who received selenium supplementation (200 µg/day) showed improvements in quality-of-life parameters.[98] Iron Deficiency Treatment Each unit increase in iron level has been shown to reduce the risk of Hashimoto thyroiditis by 43% in women of reproductive age.[99] Vitamin D Deficiency Treatment Correction of vitamin D deficiency may be beneficial, although larger-scale studies are needed to establish clear benefits. Two small randomized controlled clinical trials have shown reduced thyroid antibody levels and improved TSH levels. Individuals with vitamin D deficiency were included in these trials. One trial conducted in India administered a high dose of cholecalciferol (60,000 IU) to individuals in the intervention group for 8 weeks.[100] The other trial, conducted in China, compared a group treated with cholecalciferol 800 IU daily with a group treated with cholecalciferol 800 IU daily plus levothyroxine 25 to 50 µg/day for 6 months.[101] Furthermore, in another study in Greece, 186 vitamin D-deficient individuals received 1200 to 400 IU of cholecalciferol daily for 4 months, during which thyroid peroxidase antibody levels decreased.[102] A systematic review and meta-analysis of 862 individuals also showed a positive effect of vitamin D supplementation on thyroid function and a reduction in antibody levels.[103] Dietary Modifications

Correction of vitamin D deficiency may be beneficial, although larger-scale studies are needed to establish clear benefits. Two small randomized controlled clinical trials have shown reduced thyroid antibody levels and improved TSH levels. Individuals with vitamin D deficiency were included in these trials. One trial conducted in India administered a high dose of cholecalciferol (60,000 IU) to individuals in the intervention group for 8 weeks.[100] The other trial, conducted in China, compared a group treated with cholecalciferol 800 IU daily with a group treated with cholecalciferol 800 IU daily plus levothyroxine 25 to 50 µg/day for 6 months.[101] Furthermore, in another study in Greece, 186 vitamin D-deficient individuals received 1200 to 400 IU of cholecalciferol daily for 4 months, during which thyroid peroxidase antibody levels decreased.[102] A systematic review and meta-analysis of 862 individuals also showed a positive effect of vitamin D supplementation on thyroid function and a reduction in antibody levels.[103] Dietary Modifications Limited evidence supports the benefits of an autoimmune or anti-inflammatory diet in the management of thyroid disorders. The theory of inflammation involves leaky gut syndrome, in which an insult to the gut mucosa allows the passage of proteins that normally do not enter the bloodstream via transporters in the gut mucosa. Experts have theorized that a response similar to molecular mimicry occurs, leading to the production of antibodies against the antigens. Unfortunately, the antigen may be structurally similar to thyroid peroxidase, leading to antibody formation against this enzyme. The concept of an autoimmune diet is based on promoting gut health and reducing the severity of the autoimmune response.[104] Further research is required on this topic before it can be incorporated into established guidelines. A small study including 40 female subjects showed improvements in thyroid function and lower thyroid peroxidase and thyroglobulin antibody levels after following a Mediterranean, gluten-free diet.[105]

Differential diagnoses that should be considered when evaluating Hashimoto thyroiditis include: Euthyroid sick syndrome Goiter Graves disease (diffuse toxic goiter) Hypopituitarism (panhypopituitarism) Lithium-induced goiter Nontoxic goiter Polyglandular autoimmune syndrome type 1 Polyglandular autoimmune syndrome type 2 Thyroid cancer (lymphoma) Toxic nodular goiter

Many individuals with Hashimoto thyroiditis are euthyroid, but they are at a higher risk for developing overt hypothyroidism in the future. The risk of developing hypothyroidism increases by 5% every year.[106] Individuals with Hashimoto thyroiditis should undergo annual thyroid function testing.

Hashimoto thyroiditis can lead to several complications, primarily related to long-term thyroid dysfunction and autoimmune activity. Chronic hypothyroidism may result in fatigue, weight gain, cold intolerance, constipation, hair loss, brittle nails, depression, cognitive changes, and menstrual irregularities. A small proportion of individuals may experience transient hyperthyroidism, known as Hashitoxicosis, or develop thyroid eye disease. Persistent thyroid inflammation can lead to thyroid nodules and, rarely, to primary thyroid lymphoma. Women of reproductive age may face fertility challenges, recurrent miscarriages, or postpartum thyroiditis. Improperly managed thyroid hormone replacement can result in hormone toxicity, underscoring the importance of individualized dosing, ongoing monitoring, and interprofessional care to prevent adverse outcomes. The association between Hashimoto thyroiditis and an increased risk of papillary thyroid carcinoma remains unclear, and studies offer conflicting evidence regarding how the presence of Hashimoto thyroiditis affects papillary thyroid carcinoma outcomes.[107][108][109] Individuals with Hashimoto thyroiditis face an elevated risk for the rare malignancy of primary thyroid lymphoma, which accounts for 0.5% to 5% of all thyroid cancers.[110][111][112][113]

Managing Hashimoto thyroiditis often involves consultations with multiple healthcare professionals to ensure comprehensive care. Endocrinologists provide specialized guidance on thyroid hormone replacement, dose adjustments, and monitoring for complications, eg, thyroid nodules or lymphoma. Primary care clinicians and internists coordinate ongoing care, manage comorbid conditions, and monitor overall patient health. Pharmacists provide expertise in medication interactions, appropriate administration of levothyroxine, and adherence strategies. In cases of reproductive concerns, fertility specialists or obstetricians may be consulted, while ophthalmologists may evaluate patients with thyroid eye disease, ensuring an integrated, patient-centered approach.

Hashimoto thyroiditis is an autoimmune disorder involving the thyroid gland that can result in thyroid dysfunction and the development of hypothyroidism. This disorder has a high familial predisposition. Individuals with Hashimoto thyroiditis are at twice the risk of developing an underactive thyroid compared to those without it. Thyroid hormone replacement is only recommended in individuals with overt hypothyroidism. Treatment of subclinical hypothyroidism can be considered in select cases with significant symptoms of hypothyroidism affecting the quality of life of women of reproductive age, especially if they are trying to conceive. Many individuals living in iodine-sufficient areas may take iodine supplements for thyroid health. Excess iodine supplementation tends to worsen Hashimoto thyroiditis. Maintaining normal iron and vitamin D levels may improve thyroid function and reduce thyroid autoantibodies in Hashimoto thyroiditis. Selenium supplementation may be considered for individuals with autoimmune thyroiditis living in areas with selenium-deficient soil.

Hashimoto thyroiditis is one of the most frequent autoimmune diseases and has been reported to be associated with gastric disorders in 10% to 40% of patients. According to research by Cellini et al, about 40% of patients with autoimmune gastritis also present with Hashimoto thyroiditis. Chronic autoimmune gastritis is characterized by partial or complete loss of parietal cells, resulting in impaired hydrochloric acid and intrinsic factor production. The patients go on to develop hypochlorhydria-dependent iron-deficient anemia, which leads to pernicious anemia and severe gastric atrophy. Thyrogastric syndrome was first described in the 1960s when thyroid autoantibodies were found in a subset of patients with pernicious anemia and atrophic gastritis. The latest guidelines have incorporated the 2 aforementioned autoimmune disorders into a syndrome now known as polyglandular autoimmune syndrome. This is characterized by 2 or more endocrine and nonendocrine disorders. The thyroid gland develops from the primitive gut; therefore, the thyroid follicular cells share similar characteristics with parietal cells of the same endodermal origin. For example, both are polarized, possess apical microvilli with enzymatic activity, and can concentrate and transport iodine across the cell membrane via the sodium/iodide symporter. Iodine not only plays an essential role in the production of thyroid hormone but also regulates gastric mucosal cell proliferation, acts as an electron donor in the presence of gastric peroxidase, and helps remove free oxygen radicals. Notably, due to the global production of thyroxine, patients with gastric mucosal disorders may experience impaired absorption. Most levothyroxine is obtained by salification with sodium hydroxide, making sodium levothyroxine. T4 absorption occurs throughout the small intestine, ranging from 62% to 84% of the ingested dose. Decreased gastric acid secretion can disrupt this percentage and may reduce the absorption of most pharmaceutical-grade levothyroxine formulations, except liquid-based or soft-gel formulations. Clinicians should note the association between thyroid and gastric autoimmune diseases. Iron deficiency anemia and thyroid hormone absorption issues should prompt further diagnostic evaluation.

Effective management of Hashimoto thyroiditis requires a collaborative, interprofessional approach to ensure patient-centered care, improve outcomes, and enhance patient safety. Clinicians, including endocrinologists, primary care providers, and internists, play a crucial role in diagnosing and monitoring the disease, adjusting levothyroxine therapy based on individual needs, and screening for complications such as lymphoma. Advanced practitioners and nurses provide ongoing patient education, reinforcing the importance of treatment adherence, recognizing symptoms of hormone imbalance, and scheduling regular follow-ups for thyroid function testing. Pharmacists contribute by reviewing medication interactions, counseling patients on proper levothyroxine administration, and ensuring safe and effective dosing to prevent hormone toxicity. Interprofessional communication and care coordination are essential to optimizing team performance and patient outcomes. Clear communication among clinicians allows for timely dose adjustments, identification of potential complications, and coordination of care across specialties. Nurses and advanced clinicians serve as a bridge between patients and physicians, addressing patient concerns, managing symptoms, and facilitating referrals when needed. By fostering teamwork and prioritizing comprehensive, patient-centered care, the healthcare team can effectively manage Hashimoto thyroiditis as a lifelong condition, ensuring patients receive the support needed to maintain thyroid function and overall well-being.