Endocrinology

Importance: Hypothyroidism is a disease of thyroid hormone deficiency. The prevalence ranges from 0.3% to 12% worldwide, depending on iodine intake, and it is more common in women and older adults. Untreated hypothyroidism can cause serious health complications such as heart failure and myxedema coma.

Observations: Hashimoto thyroiditis (an autoimmune disease) is the cause of primary hypothyroidism in up to 85% of patients with hypothyroidism living in areas with adequate nutritional iodine levels. The risk of developing hypothyroidism is associated with genetic factors (having a first-degree relative with hypothyroidism), environmental factors (iodine deficiency), undergoing neck surgery or receiving radiation therapy, pregnancy in the setting of underlying autoimmune thyroid disease, and with the use of certain medications (eg, immune checkpoint inhibitors and amiodarone). Patients with hypothyroidism may have nonspecific symptoms due to metabolic slowing, including fatigue (68%-83%), weight gain (24%-59%), cognitive issues (45%-48%) such as memory loss and difficulty concentrating, and menstrual irregularities (approximately 23%) such as oligomenorrhea and menorrhagia. Hypothyroidism can cause insulin resistance and hyperglycemia in patients with diabetes, increase the risk for cardiovascular events, such as heart failure, and negatively affect female reproductive health, causing disrupted ovulation, infertility, and increased risk of miscarriage. Untreated hypothyroidism may progress to severe hypothyroidism with decompensation (myxedema coma), which is a condition associated with hypothermia, hypotension, and altered mental status that requires treatment in an intensive care unit and has a mortality rate of up to 30%. Hypothyroidism is diagnosed based on biochemical testing; a high thyrotropin (TSH) level and a low free thyroxine (T4) level indicate overt primary hypothyroidism. Screening for hypothyroidism is not recommended for asymptomatic individuals. Targeted testing is recommended for patients who are considered high risk (eg, patients with type 1 diabetes). First-line treatment for hypothyroidism is synthetic levothyroxine to normalize thyrotropin levels. Initial dosages should be tailored to patient-specific factors. Lower starting doses should be used for older patients or those with atrial fibrillation and coronary artery disease. Thyrotropin monitoring should be performed 6 to 8 weeks after initiating levothyroxine treatment, or when changing the dose, and then annually once the thyrotropin level is at goal to avoid overtreatment or undertreatment, both of which are associated with cardiovascular health risks.

Conclusions and relevance: Hypothyroidism may be associated with fatigue, weight gain, memory loss, difficulty concentrating, cardiovascular disease such as heart failure, menstrual irregularities, infertility, and increased risk of miscarriage. Levothyroxine is the first-line treatment to normalize the thyrotropin level and improve clinical manifestations due to hypothyroidism.

More than 30 million people in the US have diabetes, approximately 5% with type 1 and approximately 95% with type 2. About 5 million individuals in the US with type 2 diabetes use insulin and 7 million take sulfonylureas; both of these medications have a greater association with hypoglycemia than metformin, glucagon-like peptide 1 receptor agonists, dipeptidyl peptidase 4 inhibitors, or sodium-glucose cotransporter 2 inhibitors. Each month, 70% of people with type 1 diabetes experience some degree of hypoglycemia.1 Level 1 hypoglycemia is defined as blood glucose of 54 to 70 mg/dL; level 2 is less than 54 mg/dL; and severe hypoglycemia (level 3) occurs when low blood glucose levels cause neurologic or physical symptoms that require help from others. Furthermore, recurrent severe hypoglycemia increases risk of future dementia.2 Hypoglycemia occurs more often in people with lower education, lower income, and food insecurity.3 This synopsis focuses on outpatient management of diabetes with high risk of hypoglycemia; the guideline also addresses prevention of hypoglycemia in hospitalized patients.4