Editing Hypothyroidism


Inadequate thyroid hormone production and/or availability in target tissues

== Epidemiology ==

* Common worldwide
* Specific causes vary     depending on geography

== Aetiology ==

* Iodine deficiency (most     common in iodine-deficient populations)
* Thyroiditis (see separate     topic)
** Autoimmune thyroiditis (most      common in iodine-replete populations)
** Subacute thyroiditis
** Riedel thyroiditis
** Acute suppurative      thyroiditis
* Iatrogenic hypothyroidism
** Thyroidectomy
** RAI

== Classification ==

* Primary (cause at thyroid     level)
** Overwhelming majority of      cases
* Secondary
** Inadequate secretion of TSH      from pituitary
* Tertiary
** Inadequate secretion of TRH      from hypothalamus

== Presentation ==

* Classically:
** Cold intolerance
** Fatigue
** Puffiness and weight gain
** Dry skin
** Hair loss
** Loss of lateral third of      eyebrow (Hertoghe's sign)
* Myxoedema
** Extreme presentation
** Altered mental status or      coma, hypothermia, bradycardia, electrolyte abnormalities
** Risk of cardiomegaly,      pericardial effusion and ascites, and shock
** Typically occurs as a      decompensation of chronic hypothyroidism due to an acute physiologic      stressor (trauma, infection, acute cardiovascular event)

== Workup ==

* TSH (highly sensitive)
** >4.12mIU/L is likely      hypothyroidism, although cut-off varies with age and pregnancy
* T3/T4 if TSH abnormal

== Diagnosis ==

* Elevated TSH with decreased     free T4/T3 is diagnostic of primary hypothyroidism
* Elevated TSH with normal free     T4/T3 is likely subclinical/mild hypothyroidism

== Management ==

* First-line
** Levothyroxine (synthetic      version of T4)
** Available in oral, IM and IV      forms

[[Category:Endocrine]]