Hypothyroidism
Inadequate thyroid hormone production and/or availability in target tissues
Epidemiology
[edit | edit source]- Common worldwide
- Specific causes vary depending on geography
Aetiology
[edit | edit source]- 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
[edit | edit source]- Primary (cause at thyroid level)
- Overwhelming majority of cases
- Secondary
- Inadequate secretion of TSH from pituitary
- Tertiary
- Inadequate secretion of TRH from hypothalamus
Presentation
[edit | edit source]- 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
[edit | edit source]- TSH (highly sensitive)
- >4.12mIU/L is likely hypothyroidism, although cut-off varies with age and pregnancy
- T3/T4 if TSH abnormal
Diagnosis
[edit | edit source]- 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
[edit | edit source]- First-line
- Levothyroxine (synthetic version of T4)
- Available in oral, IM and IV forms