THYROID GLAND

The energy organ

The thyroid gland makes T3 and T4, which supercharge our body’s overall activity levels by (1) increasing Na/K Pumps and (2) increasing beta-receptors. The gland is located in the anterior neck below the laryngeal cartilage.

HYPO VS. HYPERTHYROIDISM

Thyroid hormones “speed up” all of the organs in your body. Everything “goes fast” with hyperthyroidism, and it all “slows down” with hypothyroidism. Hashimoto’s is the prototypical hypo disease, while Graves is the classic hyper disease. They are both autoimmune, and particularly common in young adult women. Learn these classic presentations!

THYROID HISTOLOGY

Mmm scallops

HYPOTHYROIDISM

Sloth-like

Hypothyroidism means low T3 / T4 and high TSH.

IODINE DEFICIENCY causes hypothyroidism because iodine is a critical component of T3 and T4. This is the most common cause of hypothyroidism worldwide. Iodine is scarce in certain landlocked countries like Russia, Ukraine, Mongolia, parts of China and parts of Africa. In the US, we cleverly spike our table salt with iodine. The thyroid gland is the only part of the human body that uses iodine. Most thyroid conditions can cause a goiter (neck swelling), but iodine deficiency causes the largest goiters of all. Treat by giving iodine supplements. When they first get the iodine, their thyroid will explode with activity, leading to a brief mild state of hyperthyroidism. This is called the Jod-Basedow phenomenon. Don’t confuse it with the Wolff-Chaikoff effect, where giving huge doses of iodine to a person with normal or overactive thyroid function will temporarily stun the production of Thyroid hormone.

There are a few iatrogenic causes of Hypothyroidism. Surgery - thyroidectomies treat hyperthyroidism, but always result in hypothyroidism.  Radioiodine Ablation - this is a treatment for Graves. You intentionally give the patient radioactive iodine, which destroys the thyroid gland after a few months! Sounds barbaric right?! It is actually a safer alternative to standard thyroidectomy surgery. Avoid in kids and pregnant women. Weirdly it worsens the ocular symptoms of Graves (exophthalmos). Drugs - Amiodarone and Lithium are two drugs that can damage the thyroid. Amiodarone is 40% Iodine (am-IOD-arone). 

CONGENITAL HYPOTHYROIDISM (Cretinism) is when a baby is born without a working thyroid gland. Worldwide, iodine deficiency is the most common cause. Since those moms lack thyroid hormones as well, the child will be born symptomatic. In the US, it’s usually associated with thyroid dysgenesis or a problem with the thyroid’s enzymes. Since mom usually has a normal thyroid in those cases, and since T3 and T4 can cross the placenta, the child is often normal at birth but degenerates in the following weeks. Symptoms are the 6 Ps: Pot-belly, Puffy-face, Protruding umbilicus, Protuberant tongue, Pale and Poor brain development. The last P is perhaps the most important. Without treatment, these children will suffer from lifelong intellectual disability. But cretinism is one of the few *treatable* causes of mental retardation. If you start Levothyroxine within the first 6 months of life, the child will have a normal intellect!

HYPERTHYROIDISM

Spazzy

Hyperthyroidism means high T3 / T4 and low TSH. 

GRAVE’S DISEASE is the classic chronic hyperthyroid condition. It’s an autoimmune attack on TSH Receptors, but interestingly, the autoimmune IgG antibodies happen to activate the TSH receptors that they bind to! The best screening test is the TSH. The most accurate test is the presence of anti-TSH receptor antibodies. The first line treatment is Methimazole, which inhibits the TPO enzyme. However, you must use Propylthiouracil during the 1st trimester of pregnancy -- high yield! Propylthiouracil is pretty hepatotoxic, so it isn’t routinely used outside of that window. Both of these drugs can rarely cause the neutrophil population to spontaneously collapse, which is called agranulocytosis. Another adjunctive treatment that can be added is Propranolol, which can help to stymie the sympathetic tone. The definitive treatment is a thyroidectomy (antiquated) or Radioiodine Ablation (a single oral dose that kills the thyroid over a few months). There are two symptoms that are pathognomonic for Graves. Exophthalmos (bulging eyeballs) and pretibial myxedema (nonpitting shin edema) are symptoms of Graves that are not found in other thyroid conditions. The pathophysiology of this swelling is incompletely understood, but likely involves the glycosylation of connective tissue in the orbit and leg, respectively. Fibroblasts are believed to be overactivated. They respond best to steroids, while radioiodine ablation worsens them. 

THYROID STORM is the most severe manifestation of hyperthyroidism. It’s a rare but dangerous occurrence, and it’s fatal if left untreated. It tends to flare up with stress (infection, trauma, surgery, burns, seizures, childbirth, emotion) in people with untreated hyperthyroidism. Patients present confused, with wildly abnormal vital signs like a high fever, tachycardia and rapid afib (cause of death). The rapid afib reduces diastolic filling time, leading to acute high output heart failure. Treat with the 4 Ps: Propranolol, Propylthiouracil, Prednisone and Potassium Iodide (which induces the Wolff-Chaikoff effect). 

TOXIC MULTINODULAR GOITER is when the thyroid develops several pockets of increased activity (often due to a TSH receptor mutation). The key diagnostic test is the Radioactive Iodine Uptake Scan (see next page). Though the symptoms are similar to Graves, the uptake scan will show multiple dark (hot) nodules. Treat acutely with Propranolol. But the definitive treatment is Radioiodine Ablation or a partial thyroidectomy. 

THYROID ADENOMA is a tumor that secretes T3 and T4. The Uptake Scan will show a single large dark spot. Noncancerous. All thyroid cancers are non-secretory. 

LEVOTHYROXINE ABUSE is a thing because it helps you lose weight. The uptake scan will show decreased activity of the thyroid. They will lack a goiter. Suspect it in someone with access to Levothyroxine, like a caretaker, nurse or pharmacy tech. And although it’s rare, be sure to consider Struma Ovarii in the differential because it also has an empty uptake scan.

PAPILLARY THYROID CANCER