- Last edited on September 3, 2023
Hypothyroidism
Primer
Hypothyroidism is a disorder of the endocrine system where the thyroid gland does not produce enough thyroid hormone. Hypothyroidism can be due to various etiologies including Hashimoto thyroiditis, postpartum thyroiditis, and congenital hypothyroidism. Hypothyroidism can result in a spectrum of neuropsychiatric symptoms, and can also be caused by psychotropic medications such as lithium.
Thyroid Hormones
Remember that the thyroid produces tri-iodothyronine (T3) and thyroxine (T4), which are iodine-containing hormones that control the body’s metabolic rate. T3 binds nuclear receptors with greater affinity than T4, and thus is the “active” hormone.
Mnemonic
The mnemonic7 B's can be used to remember the main functions of thyroid hormone:Basal metabolic rateBlood sugar (increases glycogenolysis and gluconeogenesis)Break down lipids (increases lipolysis)Brain maturationBone growth (synergism with growth hormone)β-adrenergic effects in heart, which increases contractility (this is why β-blockers alleviate adrenergic symptoms in thyrotoxicosis)- Stimulates surfactant synthesis in
Babies
Etiologies
Hashimoto Thyroiditis
Hashimoto thyroiditis (also known as Hashimoto's Disease) is an autoimmune disorder with antithyroid peroxidase (antimicrosomal) and antithyroglobulin antibodies. It is the most common cause of hypothyroidism in iodine-sufficient regions (i.e. - most Western and affluent nations). On physical exam, individuals may have a moderately enlarged, nontender thyroid.
Postpartum Thyroiditis
Postpartum thyroiditis is a self-limiting thyroiditis that can last for up to 1 year after delivery. Individuals can go between transient hyperthyroidism or hypothyroidism. Following the self-limited phase, most individuals will return back to a euthyroid state. On physical exam, the thyroid is typically painless and normal in size.
Congenital Hypothyroidism
Congenital hypothyroidism in the fetus can occur due to antibody-mediated maternal hypothyroidism, and thyroid dysgenesis.
Subacute thyroiditis (de Quervain)
Self-limited disease often following a viral infection (e.g. - flu). Individuals may be hyperthyroid early in course of illness, followed by hypothyroidism. Hypothyroidism can remain permanent in about 15% of cases. On physical exam, individuals will have jaw pain, and tender thyroid. ESR may also be elevated.
Iodine deficiency
When an individual does not have adequate iodine, the thyroid will progressively enlarge as it tries to keep up with an increased demand for thyroid hormone production. This results in a prominent goiter that develops, and is seen on physical exam. Iodine deficiency is the most common cause of thyroid enlargement and goiter worldwide.
Lithium-induced
Lithium decreases production and release of thyroxine (T4) from the thyroid gland. It also interferes with de-iodination of T4 to T3 (tri-iodothyronine). T3 is the metabolically active form of thyroid hormone.[1]
Comparison
Hypothyroidism vs. Hyperthyroidism
| Hypothyroidism | Hyperthyroidism | |
|---|---|---|
| Neuropsychiatric | Hypo-activity, lethargy, fatigue, weakness, depressed mood, reflexes (delayed, diminished) | Hyperactivity, restlessness, anxiety, insomnia, fine tremors (due to increased β-adrenergic activity), reflexes (brisk) |
| Ocular | Periorbital edema | Ophthalmopathy in Graves disease (including periorbital edema, exophthalmos), lid lag/retraction |
| Metabolic | Cold intolerance, decreased sweating, weight gain (due to lowered basal metabolic rate), hyponatremia (due to decreased free water clearance) | Heat intolerance, sweating, weight loss |
| Cardiovascular | Bradycardia, dyspnea on exertion (cardiac output) | Tachycardia, palpitations, dyspnea, arrhythmias (e.g. - atrial fibrillation), chest pain, hypertension |
| Gastrointestinal | Constipation. decreased appetite | Diarrhea, increased appetite |
| Dermatologic | Dry cool skin, coarse brittle hair, diffuse alopecia, brittle nails; puffy facies and generalized nonpitting edema (myxedema) | Warm moist skin, fine hair, onycholysis, pretibial myxedema in Graves disease |
| Reproductive | Abnormal uterine bleeding, decreased libido, infertility | Abnormal uterine bleeding, gynecomastia, decreased libido, infertility |
| Laboratory Findings | • Elevated TSH • Decreased free T3 and T4 • Hypercholesterolemia (due to decreased LDL receptor expression) | • Decreased TSH • Elevated free T3 and T4 • Decreased LDL, HDL, and total cholesterol |
Neuropsychiatric Symptoms
Psychosis
- In patients with psychosis, hypothyroidism should be considered as a possible secondary cause of psychosis.[2]
- This is especially true for patients with a history of thyroid problems or thyroidectomy regardless of the presence of other signs and symptoms of hypothyroidism or the level of T3 and T4 in the thyroid function test.[3]
Treatment
- In the absence of symptoms, elevated TSH levels <10 should not be treated.
- Routine management is to repeat a TSH level in q3-6 months
- You should however, check an anti-TPO Ab to rule out Hashimoto‘s, as subclinical hypothyroid may be treated if Anti-TPO is high, because there is an increased risk of progression to overt hypothyroidism in the future.[4]