Hypothyroidism – Causes, Symptoms, Diagnosis, Treatment

Hypothyroidism also called underactive thyroid or low thyroid is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone It can cause a number of symptoms, such as poor ability to tolerate cold, a feeling of tiredness, constipation, depression, and weight gain. Occasionally there may be swelling of the front part of the neck due to goitre. Untreated hypothyroidism during pregnancy can lead to delays in growth and intellectual development in the baby or cretinism

Thyroid Storm 

Thyroid storm refers to an increasingly rare but still highly dangerous form of thyrotoxicosis that, in addition to the other complaints of hyperthyroidism, is marked by extreme temperature elevation and/or change in mental status, ranging from extreme agitation to coma. Hypothyroid crisis refers to advanced thyroid hormone deficiency manifested by hypothermia and obtundation.

Essentially an exaggeration of thyrotoxicosis featuring marked hyperthermia (104-106°F), tachycardia (HR > 140bpm), and altered mental status (agitation, delirium, coma).

Precipitants

• Medical: Sepsis, MI, CVA, CHF, PE, visceral ischemia
• Trauma: Surgery, blunt, penetrating
• Endocrine: DKA, HHS, hypoglycemia
• Drugs: Iodine, amiodarone, inhaled anesthetics
• Pregnancy: post-partum, hyperemesis gravidarum

Scoring (Burch, Wartofsky)

Management Supportive measures

• Benzodiazepines for agitation Volume resuscitation (with VMI, Thiamine) and cooling Beta-blockade
• Propranolol 60-80mg PO q4h
• Propranolol 0.5-1.0mg IV, repeat q15min then 1-2mg q3h
• Esmolol continuous infusion
• MTZ/PTU 1-hour prior to iodine
• Methimazole 20mg (except pregnancy)
• Propylthiouracil 600mg (hepatotoxic)
• Steroids: dexamethasone
• Iodine
• Endocrinology consultation

Causes of Hypothyroidism

• Hashimoto: auto-antiboids
• Thyroidectomy
• Radiation, radioactive iodine ablation

In consumptive hypothyroidism, high levels of type 3 deiodinase inactivate thyroid hormones and thus leads to hypothyroidism. High levels of type 3 deiodinase generally occur as the result of a hemangioma. The condition is very rare.

Symptoms of Hypothyroidism 

Treatments of Hypothyroidism

Myxedema Coma

Precipitants

• Critical illness: sepsis (especially PNA), CVA, MI, CHF, trauma, burns
• Endocrine: DKA, hypoglycemia
• Drugs: amiodarone, lithium, phenytoin, rifampin, medication non-adherence
• Environmental: cold exposure

Recognition

• History: hypothyroidism, thyroidectomy scar, and acute precipitating illness
• Hypothermia: temp <95.9°F (or normal in presence of infection)
• AMS: lethargy, confusion, coma, agitation, psychosis, seizures
• Hypotension: refractory to volume resuscitation and pressors
• Bradypnea: with hypercapnia and hypoxia
• Skin: non-pitting edema of face and hands
• Hyponatremia

Management

• Airway protection
• Fluid resuscitation
• Thyroid hormone replacement
• Young, otherwise healthy patients: T3 10ug IV q4h
• Elderly, cardiac compromise: 300ug IV x1
• Steroids: dexamethasone 1h prior to thyroid hormone
• Treat precipitating illness

Hormone Replacement

Most people with hypothyroidism symptoms and confirmed thyroxine deficiency are treated with a synthetic long-acting form of thyroxine, known as levothyroxine (L-thyroxine). In young and otherwise healthy people with overt hypothyroidism, a full replacement dose (adjusted by weight) can be started immediately; in the elderly and people with heart disease, a lower starting dose is recommended to prevent over supplementation and risk of complications. Lower doses may be sufficient in those with subclinical hypothyroidism, while people with central hypothyroidism may require a higher than average dose

Liothyronine

Adding liothyronine (synthetic T₃) to levothyroxine has been suggested as a measure to provide better symptom control, but this has not been confirmed by studies. In 2007, the British Thyroid Association stated that combined T₄ and T₃ therapy carried a higher rate of side effects and no benefit over T₄ alone. Similarly, American guidelines discourage combination therapy due to a lack of evidence, although they acknowledge that some people feel better when receiving combination treatment.^[rx] Treatment with liothyronine alone has not received enough study to make a recommendation as to its use; due to its shorter half-life it needs to be taken more often

Subclinical hypothyroidism

There is little evidence whether there is a benefit from treating subclinical hypothyroidism, and whether this offsets the risks of overtreatment. Untreated subclinical hypothyroidism may be associated with a modest increase in the risk of coronary artery disease. A 2007 review found no benefit of thyroid hormone replacement except for “some parameters of lipid profiles and left ventricular function”. There is no association between subclinical hypothyroidism and an increased risk of bone fractures, nor is there a link with cognitive decline.

Since 2008, consensus American and British opinion have been that in general people with TSH under 10 mIU/l do not require treatment. American guidelines recommend that treatment should be considered in people with symptoms of hypothyroidism, detectable antibodies against thyroid peroxidase, a history of heart disease or are at an increased risk for heart disease if the TSH is elevated but below 10 mIU/l.

Desiccated animal thyroid

Desiccated thyroid extract is an animal-based thyroid gland extract, most commonly from pigs. It is combination therapy, containing forms of T₄ and T₃. It also contains calcitonin (a hormone produced in the thyroid gland involved in the regulation of calcium levels), T₁ and T₂; these are not present in synthetic hormone medication. This extract was once a mainstream hypothyroidism treatment, but its use today is unsupported by evidence; British Thyroid Association and American professional guidelines discourage its use

Interpretation of Thyroid Function Tests