Spokane Valley Ear, Nose and Throat and Facial Plastics
          

 
 Thyroid surgery (or thyroid disease)

The thyroid is one of the largest endocrine glands in the body. This gland is found in the neck inferior to (below) the thyroid cartilage (also known as the Adam's apple in men) and at approximately the same level as the cricoid cartilage. The thyroid controls how quickly the body burns energy, makes proteins, and how sensitive the body should be to other hormones.

The thyroid participates in these processes by producing thyroid hormones, principally thyroxine (T4) and triiodothyronine (T3). These hormones regulate the rate of metabolism and affect the growth and rate of function of many other systems in the body. Iodine is an essential component of both T3 and T4. The thyroid also produces the hormone calcitonin, which plays a role in calcium homeostasis.

The thyroid is controlled by the hypothalamus and pituitary. The gland gets its name from the Greek word for "shield", after the shape of the related thyroid cartilage. Hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) are the most common problems of the thyroid gland.

Anatomy

The thyroid gland is butterfly-shaped organ and is composed of two cone-like lobes or wings: lobus dexter (right lobe) and lobus sinister (left lobe), connected with the isthmus. The organ is situated on the anterior side of the neck, lying against and around the larynx and trachea, reaching posteriorly the oesophagus and carotid sheath. It starts cranially at the oblique line on the thyroid cartilage (just below the laryngeal prominence or Adam's apple) and extends inferiorly to the fourth to sixth tracheal ring. It is difficult to demarcate the gland's upper and lower border with vertebral levels as it moves position in relation to these during swallowing.

The thyroid gland is covered by a fibrous sheath, the capsula glandulae thyroidea, composed of an internal and external layer. The external layer is anteriorly continuous with the lamina pretrachealis fasciae cervicalis and posteriorolaterally continuous with the carotid sheath. The gland is covered anteriorly with infrahyoid muscles and laterally with the sternocleidomastoid muscle. Posteriorly, the gland is fixed to the cricoid and tracheal cartilage and cricopharyngeus muscle by a thickening of the fascia to form the posterior suspensory ligament of Berry. In variable extent, Lalouette's Pyramid, a pyramidal extension of the thyroid lobe, is present at the most anterior side of the lobe. In this region the recurrent laryngeal nerve and the inferior thyroid artery pass next to or in the ligament and tubercle. Between the two layers of the capsule and on the posterior side of the lobes there are on each side two parathyroid glands.

The thyroid isthmus is variable in presence and size, and can encompass a cranially extending pyramid lobe (lobus pyramidalis or processus pyramidalis), remnant of the thyroglossal duct. The thyroid is one of the larger endocrine glands, weighing 2-3 grams in neonates and 18-60 grams in adults, and is increased in pregnancy.

The thyroid is supplied with arterial blood from the superior thyroid artery, a branch of the external carotid artery, and the inferior thyroid artery, a branch of the thyrocervical trunk, and sometimes by the thyroid ima artery, branching directly from the aortic arch. The venous blood is drained via superior thyroid veins, draining in the internal jugular vein, and via inferior thyroid veins, draining via the plexus thyroideus impar in the left brachiocephalic vein. Lymphatic drainage passes frequently the lateral deep cervical lymph nodes and the pre- and parathracheal lymph nodes. The gland is supplied by sympathetic nerve input from the superior cervical ganglion and the cervicothoracic ganglion of the sympathetic trunk, and by parasympathetic nerve input from the superior laryngeal nerve and the recurrent laryngeal nerve.

Diseases

Hypothyroidism (underactivity)
Hypothyroidism is the disease state in humans and in animals caused by insufficient production of thyroid hormone by the thyroid gland. Cretinism is a form of hypothyroidism found in infants.

Causes

About three percent of the general population is hypothyroid. Factors such as iodine deficiency or exposure to Iodine-131  can increase that risk. There are a number of causes for hypothyroidism. Historically, and still in many developing countries, iodine deficiency is the most common cause of hypothyroidism worldwide. In iodine-replete individuals, hypothyroidism is mostly caused by Hashimoto's thyroiditis, or by a lack of the thyroid gland or a deficiency of hormones from either the hypothalamus or the pituitary.

Hypothyroidism can result from postpartum thyroiditis, a condition that affects about 5% of all women within a year after giving birth. The first phase is typically hyperthyroidism. Then, the thyroid either returns to normal or a woman develops hypothyroidism. Of those women who experience hypothyroidism associated with postpartum thyroiditis, one in five will develop permanent hypothyroidism requiring life-long treatment.

Hypothyroidism can also result from sporadic inheritance, sometimes autosomal recessive.

Hypothyroidism is also a relatively common hormone disease in domestic dogs, with some specific breeds having a definite predisposition.

Temporary hypothyroidism can be due to the Wolff-Chaikoff effect. A very high intake of iodine can be used to temporarily treat hyperthyroidism, especially in an emergency situation. Although iodine is substrate for thyroid hormones, high levels prompt the thyroid gland to take in less of the iodine that is eaten, reducing hormone production.

Hypothyroidism is often classified by the organ of origin:

General psychological associations

Hypothyroidism can be caused by lithium-based mood stabilizers, usually used to treat bipolar disorder (previously known as manic depression).

In addition, patients with hypothyroidism and psychiatric symptoms may be diagnosed with:

  • atypical depression (which may present as dysthymia)
  • bipolar spectrum syndrome (including bipolar I or bipolar II disorder, cyclothymia, or premenstrual syndrome)
  • inattentive ADHD or sluggish cognitive tempo

Symptoms

In adults, hypothyroidism is associated with the following symptoms:

Early symptoms

  • Poor muscle tone (muscle hypotonia)
  • Fatigue
  • Cold intolerance, increased sensitivity to cold
  • Depression
  • Muscle cramps and joint pain
  • Goiter
  • Thin, brittle fingernails
  • Thin, brittle hair
  • Paleness
  • Dry, itchy skin
  • Weight gain and water retention.
  • Bradycardia (low heart rate: less than sixty beats per minute)
  • Constipation

Late symptoms

  • slow speech and a hoarse, breaking voice. Deepening of the voice can also be noticed.
  • Dry puffy skin, especially on the face
  • Thinning of the outer third of the eyebrows.
  • Abnormal menstrual cycles
  • Low basal body temperature

Less common symptoms

  • Impaired memory
  • Impaired cognitive function (brain fog) and inattentiveness
  • A slow heart rate with ECG changes including low voltage signals. Diminished cardiac output and decreased contractility.
  • Reactive (or post-prandial) hypoglycemia
  • Sluggish reflexes
  • Hair loss
  • Anemia caused by impaired hemoglobin synthesis (decreased EPO levels), impaired intestinal iron and folate absorption or B12 deficiency from pernicious anemia
  • Difficulty swallowing
  • Shortness of breath with a shallow and slow respiratory pattern.
  • Increased need for sleep
  • Irritability and mood instability
  • Yellowing of the skin due to impaired conversion of beta-carotene to vitamin A
  • Impaired renal function with decreased GFR.
  • Elevated serum cholesterol
  • Acute psychosis (myxedema madness) is a rare presentation of hypothyroidism
  • Decreased libido
  • Decreased sense of taste and smell (late, less common symptoms)
  • Puffy face, hands and feet (late, less common symptoms)

Diagnostic testing

To diagnose primary hypothyroidism, many doctors simply measure the amount of Thyroid-stimulating hormone (TSH) being produced by the pituitary gland. High levels of TSH indicate that the thyroid is not producing sufficient levels of Thyroid hormone (mainly as thyroxine (T4) and smaller amounts of triiodothyronine (T3)). However, measuring just TSH fails to diagnose secondary and tertiary forms of hypothyroidism, thus leading to the following suggested blood testing if the TSH is normal and hypothyroidism is still suspected:

  • free triiodothyronine (fT3)
  • free levothyroxine (fT4)
  • total T3
  • total T4

Additionally, the following measurements may be needed:

  • 24 hour urine free T3;
  • antithyroid antibodies — for evidence of autoimmune diseases that may be damaging the thyroid gland
  • serum cholesterol — which may be elevated in hypothyroidism
  • prolactin — as a widely available test of pituitary function
  • testing for anemia, including ferritin
  • basal body temperature

Treatment

Hypothyroidism is treated with the levorotatory forms of thyroxine (L-T4) and triiodothyronine (L-T3). Both synthetic and animal-derived thyroid tablets are available and can be prescribed for patients in need of additional thyroid hormone. Thyroid hormone is taken daily, and doctors can monitor blood levels to help assure proper dosing. There are several different treatment protocols in thyroid replacement therapy:

T4 Only
This treatment involves supplementation of levothyroxine alone, in a synthetic form. It is currently the standard treatment in mainstream medicine.
T4 and T3 in Combination
This treatment protocol involves administering both synthetic L-T4 and L-T3 simultaneously in combination.
Desiccated Thyroid Extract
Desiccated thyroid extract is an animal based thyroid extract, most commonly from a porcine source. It is also a combination therapy, containing natural forms of L-T4 and L-T3

Treatment controversy

The current standard treatment in thyroid therapy is levothyroxine only, and the American Association of Clinical Endocrinologists (AACE) states that desiccated thyroid hormone, combinations of thyroid hormone, or triiodothyronine should not generally be used for replacement therapy. Nevertheless, there exists some controversy about whether this treatment protocol is optimal, and recent studies have given conflicting results.

Two recent studies comparing synthetic T4 versus synthetic T4 + T3 have shown "clear improvements in both cognition and mood" from combination therapy. Another study comparing synthetic T4 and desiccated thyroid extract showed marked improvements in virtually all symptom categories when certain patients were switched from synthetic T4 to desiccated thyroid extract.

However, other studies have shown no improvement in mood or mental abilities for those on combination therapy, and possibly impaired well-being from subclinical hyperthyroidism. Also, a 2007 metaanalysis of the nine controlled studies so far published found no significant difference in the effect on psychiatric symptoms.

There is also concern among some practitioners about the use of T3 due to its short half life. T3 when used on its own as a treatment results in wide fluctuations across the course of a day in the thyroid hormone levels, and with combined T3/T4 therapy there continues to be wide variation throughout each day.

Subclinical hypothyroidism

Subclinical hypothyroidism occurs when thyrotropin (TSH) levels are elevated but thyroxine (T4) and triiodothyronine (T3) levels are normal. In primary hypothyroidism, TSH levels are high and T4 and T3 levels are low. Endocrinologists are puzzled because TSH usually increases when T4 and T3 levels drop. TSH prompts the thyroid gland to make more hormone. Endocrinologists are unsure how subclinical hypothyroidism affects cellular metabolic rates (and ultimately the body's organs) because the levels of the active hormones are adequate. Some have proposed treating subclinical hypothyroidism with levothyroxine, the typical treatment for overt hypothyroidism, but the benefits and the risks are unclear. Reference ranges have been debated as well. The American Association of Clinical Endocrinologists (ACEE) supports a narrower TSH range, especially when the person has clinical signs of thyroid disease. This reference range may reduce the risks of goiter, thyroid nodules, thyroid cancer, and overt hypothyroidism, but remains controversial. There is always the risk of overtreatment and hyperthyroidism. Some studies have suggested that subclinical hypothyroidism does not need to be treated. A meta-analysis by the Cochrane Collaboration found no benefit of thyroid hormone replacement except "some parameters of lipid profiles and left ventricular function".  A more recent metanalysis looking into whether subclinical hypothyroidism may increase the risk of cardiovascular disease, as has been previously suggested, found a possible modest increase and suggested further studies be undertaken with coronary heart disease as a end point "before current recommendations are updated".

 

Sub-laboratory hypothyroidism

"Sub-laboratory" hypothyroidism occurs when blood levels of thyroid hormones and thyrotropin (TSH) are within reference ranges, yet hypothyroid symptoms are present and resolve with thyroid therapy. This type of hypothyroidism is thought not to be another form of the disease, but instead simply illuminates the failure of blood tests to fully reflect the health of the hypothalamic-pituitary-thyroid axis. The lack of correlation between hypothyroid symptoms and serum thyrotropin (TSH) and T4, has been pointed out by several researchers.