Hypothyroidism

Definition

Primary Hypothyroidism: High TSH and Low T4

Secondary (central) Hypothyroidism: Low T4 and TSH that is low

Subclinical Hypothyroidism: High TSG with normal T4

Myxedema coma: severe hypothyroidism causing multi-organ dysfunction. A medical emergency with a high mortality rate

Presentation

Early: Usually asymptomatic,  but may have fatigue, weight gain, cold intolerance, menorrhagia or amenorrhea, constipation, dry skin, thin hair, delayed DTR, diastolic HTN and hyperlipidemia

Late: Slow speech, brawny edema, hoarseness, loss of outer third of eyebrows, puffy face/eyelids, thickened tongue, myxedema, bradycardia, hypotension, and hypothermia

Myxedema coma: Endocrine emergency. Can present with AMS, hypothermia, hypoventilation, hyponatremia, hypoxia, hypercapnia, hypotension, convulsion, confusion, lethargy and coma.

Management

Levothyroxine: Full replacement is approx 1.6mcg/kg/day. Patient not requiring full replacement can be started on lower dose

Monitoring and dose adjustment based on TSH every 4-8 weeks until stable dose achieved

Pregnancy: Goal TSH varies by trimester, consultation with endocrinology is indicated

Elderly with CAD or high risk CAD, long standing untreated hypothyroidism: Start levothyroxine 25mcg/day

Subclinical hypothyroidism: Treatment generally not necessary unless TSH is >10, anti TPO positive, presence of a goiter, pregnancy or other compelling complication. Typically lower doses of levothyroxine are needed. Start with 15-50mcg. Follow up in 4-8 weeks of treatment initiation.

Thyroid Cancer: Patient who had total thyroidectomy for thyroid cancer need higher doses of thyroid hormone to suppress TSH

Myexedema coma:

• Immediate endocrine consult to help guide therapy,
• draw cortisol level first and administer steroid (hydrocortisone 50-100mg q6-8h) until adrenal insufficiency can be ruled out. Thyroid hormone therapy can increase cortisol clearance, precipitating adrenal insuffiency.
• Thyroid replacement: 200-400mcg IV load followed by 50-100mcg IV daily. Consider lower IV load doses in elderly patients or patient with cardiac conditions

https://pubmed.ncbi.nlm.nih.gov/23246686/

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