Thyroid

Hypothyroidism 

The thyroid gland plays an important role in tissue metabolism and development. It secretes thyroxine, which is abbreviated as T4, and small amounts of 3,5,3'-triiodothyronine, abbreviated T3. Both have systemic effects.

Abnormal thyroid hormone levels lead to hypothyroid and hyperthyroid states.

This is how T3 and T4 looks like:

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     For many reason, the level of thyroid hormones could be low. This is called hypothyroidism and it comes with multiple associated symptoms that you need to understand. It usually is a primary process in which the thyroid gland produces insufficient amounts of thyroid hormone. It can also be secondary, that is lack of thyroid hormone secretion due to the failure of either  thyrotropin (ie, thyroid-stimulating hormone [TSH]) secretion from the pituitary gland or thyrotropin-releasing hormone (TRH) from the hypothalamus a part of the brain.

     Hashimoto’s disease an autoimmune disease is the most common cause of hypothyroidism in North America.The term myxedema refers to the thickened, nonpitting edematous changes to the soft tissues of patients in a markedly hypothyroid state. Myxedema coma, a rare, life-threatening condition, occurs late in the progression of hypothyroidism. 

   Inadequate thyroid hormone during development leads to congenital hypothyroidism (also known as cretinism) with associated irreversible brain damage.

   4.6 % of the population is affected by hypothyroidism. It is more common in women with small body size at birth and low body mass index during childhood. Disorder is nearly 10 times more common in females than in males. Although not common in North America, Iodine deficiency is more common in the other parts of the world, with a prevalence of 2.5% in early ages and up to 15% when reaching age 75. Hypothyroidism is less rare in white people (prevalence = 5.1%) than in Hispanic people (4.1%) or African Americans (1.7%).

     The frequency of hypothyroidism, goiters, and thyroid nodules increases with age. Hypothyroidism is most prevalent in elderly populations, with 2% to as much as 20% of older age groups having some form of hypothyroidism Mortality due to hypothyroidism is uncommon.  

Primary hypothyroidism 

     Chronic autoimmune (Hashimoto's) thyroiditis is the leading cause of primary hypothyroidism in iodine-sufficient areas. This could present itself with or without a goiter. In this disease our own body attacks the thyroid gland by producing antibodies against it. Most patients have measurable autoantibodies against different components of the thyroid gland (thyroid peroxidase, thyroglobulin, TSH receptor, TSH blocking antibodies).

     Hypothyroidism due to autoimmune thyroiditis may be part of a polyglandular failure syndrome that may include autoimmune adrenal insufficiency, type 1 diabetes mellitus, hypogonadism, pernicious anemia, and vitiligo.Iodine deficiency is the most common cause of hypothyroidism worldwide. Patients often have large goiters.It is also frequent to have hypothyroidism after ablative surgery of the thyroid gland. They often develop several weeks after radioactive iodine therapy. Periodic monitoring of thyroid function tests is important after thyroidectomy and radioactive iodine therapy for early detection and treatment of hypothyroidism.

     Hypothyroidism can also appear many years after head and neck irradiation.

Drug that could give Hypothyroidism

     Amiodarone and lithium are among a number of drugs that can cause hypothyroidism. Both drugs are widely used in clinical practice. Thyroid function tests should be obtained before initiating therapy with these agents and periodically thereafter.

     Other incriminated drugs include perchlorate (rarely used clinically), ethionamide, interferon alfa, and interleukin-2. Thyroid function usually normalizes after discontinuation if these drugs. infiltrative and infectious diseases such as fibrous thyroiditis of Riedel, sarcoidosis (which can also cause central hypothyroidism), hemochromatosis, leukemia, lymphoma, cystinosis, amyloid, scleroderma, and Mycobacterium tuberculosis and Pneumocystis carinii infection can also cause hypothyroidism.  

Central hypothyroidism 

     In central hypothyroidism there is an diminish release of TSH. It could be secondary due to defect  in the pituitary gland, or tertiary hypothyroidism, where the defect is in the hypothalamus. pituitary adenoma, a benign tumour of the pituitary gland, is the most common cause of central hypothyroidism. Less prevalent conditions include pituitary apoplexy and infiltrative disorders of the hypothalamus-pituitary axis, such as sarcoidosis, tuberculosis, and other granulomatous diseases.  

Symptoms 

• Fatigue, loss of energy, lethargy
• Weight gain
• Decreased appetite
• Cold intolerance
• Dry skin
• Hair loss
• Sleepiness 
• Muscle pain, joint pain, weakness in the extremities
• Depression
• Emotional lability, mental impairment
• Forgetfulness, impaired memory, inability to concentrate
• Constipation
• Menstrual disturbances, impaired fertility
• Decreased perspiration
• Paresthesia and nerve entrapment syndromes
• Blurred vision
• Decreased hearing
• Fullness in the throat, hoarseness

 If you do have some of these symptoms it is important to consult your physician. 

Diagnosis

   The diagnosis of hypothyroidism is based on the combination of clinical context and laboratory tests. Imaging of the brain and pituitary gland is required for patients in whom central hypothyroidism is suspected.In the majority of patients, making the diagnosis of hypothyroidism should not be complicated. A number of factors can affect the levels of TSH, total T4, and total T3; in particular, several medical conditions can increase or decrease the concentration of total T4 and total T3 through their effect on serum levels of thyroxine-binding globulin and albumin. Examples include estrogens, nephrotic syndrome, and other states of hypoproteinemia.

     The serum levels of free T4 remain normal in these circumstances and provide a better assessment of thyroid function.We measure TSH, freeT4 (FT4), and total T3 (TT3) in patients who are suspected of having thyroid dysfunction

• TSH is elevated in primary hypothyroidism, but it may be normal or low in secondary causes of hypothyroidism.
• Free thyroxine (T4) levels are low.
• Triiodothyronine (T3) resin uptake is increased.
• Free T4 index (T3 resin uptake x total serum T4) is low.

 Treatment:

     All patients in myxedema coma should be given stress-dose steroids for the first 24 to 48 hours because supplementation of thyroid hormones leads to increased metabolism and thereby increases the requirement of cortisol.Treatment of hypothyroidism is via hormonal replacement. This could be done in numbers of ways. Synthetic hormonotherapy (with synthetic T4) is the more common therapy used today.  It could also be combined with T3 treatment (not frequently advocated). The other alternative is Natural Desiccated thyroid extract like Thyroid® distributed in Canada.