Internal Medicine

0521779407-09 CUNY1086/Karliner 0 521 77940 7 June 13, 2007 7:54

Hypothyroidism 803

tests

Laboratory

■Basic blood tests: free T4, TSH

■Specific Diagnostic Tests

➣Anti-TPO antibody, antithyroglobulin antibody, lipid panel, CPK,

sodium

Imaging

■MRI of pituitary region if free T4 low and TSH low or normal

■I-123 uptake and scan not needed

differential diagnosis

■Primary hypothyroidism (low T4, high TSH):

➣Hashimoto disease

➣Subacute thyroiditis: viral, silent, postpartum

➣Status postthyroidectomy or I-131 therapy

➣Goitrogen induced: lithium, PTU, MTZ

➣Iodine induced: amiodarone, contrast, kelp

➣Rare causes: iodine deficiency, Riedel struma, enzyme defect

■Secondary hypothyroidism (low T4, low or normal TSH):

➣Pituitary or hypothalamic tumors

➣Status postpituitary or hypothalamic surgery

➣Granulomatous diseases

➣Postpartum necrosis

➣Other pituitary and hypothalamic disorders

management

What to Do First

■Assess degree of severity using clinical presentation, extent of free

T4 lowering or TSH elevation

General Measures

■Assess for associated disorders, hypothermia, hyponatremia, mental

status, hypoventilation

specific therapy

■Levothyroxine: full dose of 1.6 mcg/kg in myxedema coma and young

patients without ischemic heart disease; low dose in elderly patients

and those with ischemic heart disease; take fasting, because absorp-

tion inhibited by food and drugs (iron, calcium, fiber); increased

dose usually required during pregnancy