Hypothyroidism

Etiologies

• Primary (>90% of cases of hypothyroidism; . free T4. * TSH)

Goitrous: Hashimoto's thyroiditis, recovery phase after thyroiditis, iodine deficiency Nongoitrous: surgical destruction, s p radioactive iodine or XRT. amiodarone. lithium

• Secondary (1 free T«. variable TSH): hypothalamic or pituitary failure (TSH levels i or

"normal." can be slightly T although functionally inactive due to abnormal glycosylation)

Hashimoto's thyroiditis

• Autoimmune destruction with patchy lymphocytic infiltration

• Usually seen in women 20-60 y old; may be part of PGA syndrome type II

(hypothyroidism. Addison's, diabetes mellitus); associated w T incidence of Sjogren's syndrome, pernicious anemia. & primary biliary cirrhosis

• © antithyroid peroxidase (anti-TPO) and antithyroglobulin (anti-Tg) abs in >90%

Clinical manifestations (Lancet 2004:363:793)

• Early: weakness, fatigue, arthralgias, myalgias, headache, depression, cold intolerance.

weight gain, constipation, menorrhagia. dry skin, coarse brittle hair, brittle nails, carpal tunnel syndrome, delayed DTRs ("hung up" reflexes), diastolic HTN, hyperlipidemia

• Late: slow speech, hoarseness, loss of outer third of eyebrows, myxedema

(nonpitting skin thickening due to T glycosaminoglycans). periorbital puffiness. bradycardia, pleural, pericardial. & peritoneal effusions, atherosclerosis

• Myxedema coma: hypothermia, hypotension, hypoventilation. A MS

Diagnostic studies

• i FT«; TTSH in primary hypothyroidism; © antithyroid Ab in Hashimoto's thyroiditis

• May sec hyponatremia, hypoglycemia, anemia, t LDL 1 HDL, and T CK

• Screening recommended for pregnant women

Treatment of overt hypothyroidism

• Levothyroxine (1.5-1.7 p.g kg d), re/TSH q5-6wks and titrate until euthyroid;

sx can take mos to resolve; lower starting dose (0.3-0.5 ug kg d) if at risk for ischemic heart disease; advise Pts to keep same formulation of levothyroxine

• Myxedema coma: load 5-8 p.g kgT< IV, then 50-100 pg IV qd; b c peripheral conversion is impaired, may also give 5-10 pgTj IV q8h (Tj more arrhythmogenic); must give empiric odrenal replacement therapy as 1 adrenal reserves in myxedema coma

Subclinical hypothyroidism (NE/m 2001:345:260)

• Mild T TSH and normal free T« with only subtle or no sx

• If t titers of antithyroid Abs. progression to overt hypothyroidism is -4% y

• Rx controversial: follow expectandy or treat to improve ? mild sx or dyslipidemia most initiate Rx if TSH 10 mU L goiter, pregnancy, or infertility risk of precipitating atrial fibrillation & angina and accelerating osteoporosis

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