hypothyroidism

(hypothyroidism)

?What is hypothyroidism

Hypothyroidism, also called underactive thyroid, is when the thyroidglanddoesn’t make enough thyroidhormonesto meet your body’s needs. The thyroid is a small, butterfly-shaped gland in the front of your neck. Thyroid hormones control the way the body uses energy, so they affect nearlyevery organ in your body, even the way your heart beats.
Without enough thyroid hormones, many of your body’s functions slow down.​The thyroid is a small gland in your neck that makes thyroidhormones.
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Is hypothyroidism during pregnancy a problem?

Hypothyroidism that isn’t treated can affect both the mother and the baby. However, thyroid medicines can help prevent problems and are safe to take during pregnancy. Learn more about causes, diagnosis, and treatment ofhypothyroidism during pregnancy.
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Causes
Hypothyroidism

 is caused by inadequate function of the gland itself (primary hypothyroidism), inadequate stimulation by thyroid-stimulating hormone from thepituitary gland(secondary hypothyroidism), or inadequate release ofthyrotropin-releasing hormonefrom the brain'shypothalamus
(tertiary hypothyroidism).

Primary hypothyroidism is about a thousandfold more common than central hypothyroidism
Iodine deficiencyis the most common cause of primary hypothyroidism andendemic goiterworldwide.
In areas of the world with sufficient dietary iodine, hypothyroidism is most commonly causedby the autoimmune disease Hashimoto's thyroiditis
(chronic autoimmune thyroiditis).Hashimoto's may be associated with a goiter.
 It is characterizedby infiltration of the thyroid gland withT lymphocytesandautoantibodiesagainst specific thyroid antigenssuch asthyroid peroxidase,thyroglobulinand theTSH receptor.

After women give birth, about 5% developpostpartum thyroiditiswhich can occur up to nine months afterwards.
This is characterized by a short period ofhyperthyroidismfollowed by a period of hypothyroidism; 20–40% remain permanently  
hypothyroid.
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Autoimmune thyroiditis
is associated with other immune-mediated diseases such as
diabetes mellitus type 1, pernicious anemia,myasthenia gravis,celiac disease,rheumatoid arthritisandsystemic lupus erythematosus.
It may occur as part of autoimmune polyendocrine syndrome
(type 1andtype 2).

1- Primary hypothyroidism:-
*Iodine deficiency (developing countries)
 *autoimmune thyroiditis
*subacute granulomatous thyroiditis
*subacute lymphocytic thyroiditis
*postpartum thyroiditis
* previous thyroidectomy
* previous radioiodinetreatment
* previousexternal beam radiotherapyto the neckMedication:lithium-basedmood stabilizers,amiodarone,interferonalpha,tyrosine kinase inhibitors such assunitinib

2-Central hypothyroidism:-

*Lesions compressing the pituitary
*pituitary adenom
*craniopharyngioma
*meningioma
*glioma
*Rathke's cleft cyst
*metastasis
*empty sella
*aneurysmof theinternal carotid artery
surgery or radiation to the pituitary
 drugs, injury, vascular disorders
(pituitary apoplexy,Sheehan syndrome,subarachnoid hemorrhage), autoimmune diseases(lymphocytic hypophysitis, polyglandular disorders), infiltrative diseases (iron overload due tohemochromatosisorthalassemia,neurosarcoidosis,Langerhans cell histiocytosis), particular inherited congenital disorders, and infections (tuberculosis,mycoses,syphilis)

3-Congenital hypothyroidism:-
Thyroid dysgenesis(75%),thyroid dyshormonogenesis(20%), maternal antibody or radioiodine transferSyndromes: mutations (inGNAS complex locus,PAX8,TTF-1/NKX2-1,TTF-2/FOXE1),Pendred's syndrome(associated withsensorineural hearing loss)Transiently: due to maternal iodine deficiency or excess,anti-TSH receptor antibodies, certain congenital disorders,neonatal illnessCentral: pituitary dysfunction (idiopathic,septo-optic dysplasia, deficiency ofPIT1, isolated TSH deficiency)
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What are the symptoms of hypothyroidism?

Hypothyroidism has many symptoms that can vary from person to person.
 Some common symptoms of hypothyroidism include
*fatigue
*weight gain
*a puffy face
*trouble tolerating cold
*joint and muscle pain
*constipation
*dry skin
*dry, thinning hair
*decreased sweating
*heavy or irregular menstrual periods
*fertility problems
*depression
*slowed heart rate
*goiterBecause hypothyroidism develops slowly, many people don’t notice symptoms of the disease for months or even years.
Many of these symptoms, especially fatigue and weight gain, are common and don’t always mean that someone has a thyroid problem.
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Diagnosis

Thyroid function tests
Laboratory testing of thyroid stimulating hormone levels in the blood is considered the best initial test for hypothyroidism; a second TSH level is often obtained severalweeks later for confirmation.
Levels may be abnormal in the context of other illnesses, and TSH testing in hospitalized people is discouraged unless thyroid dysfunction is strongly suspected.
An elevated TSH level indicates that the thyroid gland is not producing enough thyroid hormone, and free T4 levels are then often obtained.Measuring T3isdiscouraged by theAACEin the assessment for hypothyroidism.
Many cases of hypothyroidism are associated with mild elevations increatinekinase and liver enzymes in the blood.
They typically return to normal when hypothyroidism has been fully treated.Levels ofcholesterol,low-density lipoprotein and lipoprotein (a)can be elevated;the impact of subclinical hypothyroidism on lipid parameters is less well-defined.Very severe hypothyroidism and my xedema coma are characteristically associated with low sodium levels in the blood together with elevations in antidiuretic hormone, as well asacute worsening of kidney functiondue to a number of causes.
A diagnosis of hypothyroidism without anylumps or massesfelt within the thyroid gland does not require thyroid imaging; however, if the thyroid feels abnormal, diagnostic imaging is then recommended.
The presence of antibodies againstthyroid peroxidase(TPO) makes it more likely that thyroid nodules are caused by autoimmune thyroiditis, but if there is any doubt, aneedle biopsymay be required.
If the TSH level is normal or low and serumfree T4levels are low, this is suggestive of central hypothyroidism (not enough TSH or TRH secretion by the pituitary gland or hypothalamus).
There may be other features of hypopituitarism, such asmenstrual cycleabnormalities andadrenalinsufficiency. There might also be evidence of apituitary masssuch asheadachesand vision changes. Central hypothyroidism should be investigated further to determine the underlying cause.

Overt
In overt primary hypothyroidism, TSH levels are high and T4and T3levels are low. Overt hypothyroidism may also be diagnosed in those who have a TSH on multiple occasions of greater than 5mIU/L,appropriate symptoms, and only a borderline low T4.
It may also be diagnosed in those with a TSH of greater than 10mIU/L.
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Management

Hormone replacement
Most people with hypothyroidism symptoms and confirmed thyroxine deficiency are treated with a synthetic long-acting form of thyroxine, known aslevothyroxine
(L-thyroxine).
In youngand other wise healthy people with overt hypothyroidism, a full replacement dose (adjusted by weight) can be started immediately; in the elderly and people withheart 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.
Blood free thyroxine and TSH levels are monitored to help determine whether the dose is adequate.
This is done 4–8 weeks after the start of treatment or a change in levothyroxine dose.
 Once the adequate replacement dose has been established, the tests can be repeated after 6 and then 12 months, unless there is a change in symptoms.
In people with central/secondary hypothyroidism, TSH is not a reliable marker of hormone replacement and decisions are based mainly on the free T4level.
Levothyroxine is best taken 30–60 minutes before breakfast, or four hours after food,as certain substances such as food and calcium can inhibit the absorption of levothyroxine.
There is no direct way of increasing thyroid hormone secretion by the thyroid gland.
LiothyronineAdding liothyronine
(synthetic T3) to levothyroxine has been suggested as a measure to provide better symptom control, but this has not been confirmed bystudies.
In 2007, the British Thyroid Association stated that combined T4and T3therapy carried a higher rate of side effects and no benefit over T4alone.Similarly, American guidelines discourage combination therapy due to a lack of evidence, although they acknowledge that some people feel better when receiving combination treatment.

Treatment with liothyroninealone 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.
People with hypothyroidism who do not feel well despite optimal levothyroxine dosing may request adjunctive treatment with liothyronine.
A 2012 guideline from the European Thyroid Association recommends that support should be offered with regards to the chronic nature of the disease and that other causes of thesymptoms should be excluded.
Addition of liothyronine should be regarded as experimental, initially only for a trial period of 3 months, and in a set ratio to the current dose of levothyroxine.The guideline explicitly aims to enhance the safety of this approach and to counter its indiscriminate use.Desiccated animal thyroid Desiccated thyroid extractis an animal-based thyroid gland extract,most commonly frompigs.
 It is a combination therapy, containing forms of T4and T3.
It also containscalcitonin(a hormone produced in the thyroid gland involved in the regulation of calcium levels), T1and 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.
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المصادر
1- Wikipedia
2- Health Network
3- WebMD
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