Thyroid

Limit testing for thyroid disease to appropriate patients, namely those with a significant pre-test probability of abnormal results, such as:
- those with classic signs or symptoms of thyroid disease.
- those whose symptoms or signs are not classic, but who are at a higher risk for disease (e.g., the elderly, postpartum women, those with a history of atrial fibrillation, those with other endocrine disorders).
In patients with established thyroid disease, do not check thyroid-stimulating hormone levels too often, but rather test at the appropriate times, such as:
- after changing medical doses.
- when following patients with mild disease before initiating treatment.
- periodically in stable patients receiving treatment.
When examining the thyroid gland, use proper technique (i.e., from behind the patient, ask the patient to swallow), especially to find nodules (which may require further investigation).

Risk Factors for Thyroid Disease

Women >45yo
Postpartum
- No clear impact (benefit or harm) for universal screening in pregnancy
Radiation
Drug-induced (lithium, amiodarone)
- Lithium can cause goiter, hypothyroidism (more common), hyperthyroidism
- Interferon alfa-2b may cause hypothyroidism or hyperthyroidism
Autoimmune disease (eg. DM1)
Strong family history of thyroid disease

Normal/high radioiodine uptake
- Autoimmune
  - Graves' disease
  - Hashitoxicosis
- Autonomous thyroid tissue
  - Toxic adenoma
  - Toxic multinodular goiter
- TSH-mediated
  - Pituitary adenoma
- Human chorionic gonadotropin
  - Hyperemesis gravidarum
  - Trophoblastic
Near absent radioiodine uptake
- Thyroiditis
  - Subacute granulomatous (de Quervain's) thyroiditis
  - Painless thyroiditis (silent, lymphocytic, postpartum)
  - Amiodarone
  - Radiation thyroiditis
  - Palpation thyroiditis
- Exogenous thyroid hormone intake (excessive replacement therapy)
- Ectopic hyperthyroidism
  - Struma ovarii
  - Metastatic follicular thyroid cancer

Subclinical hypothyroidism (possible CAD, heart failure, stroke, lipids, infertility)
- Consider treatment if TSH≥20mU/L (BMJ 2019), symptomatic, or risk (elevated Anti-TPO Ab, Goiter, strong family history of autoimmune, pregnancy)
- Consider treatment in infertility
Subclinical hyperthyroidism (risk of atrial fibrillation/flutter, heart failure, lower BMD)
- Consider treatment if TSH <0.1 mIU/L and
  - Symptomatic (palpitations, tremor, nervousness)
  - >65yo
  - Comorbidities such as heart disease or osteoporosis
  - Postmenopausal (<65yo) and not taking estrogen/bisphosphonates

Subacute granulomatous thyroiditis (viral infection, painful thyroid) - NSAIDs
Levothyroxine treatment of choice, start 12.5-50mcg/day
- No strong evidence for alternatives (levothyroixine-liothyronine or thyroid extract therapy)
- Target TSH euthyroid range (except in secondary hypothyroidism, where target FT4)
  - No evidence for levothyroxine in euthyroid (except in thyroid cancer target undetectable TSH to reduce recurrence by 40%)
  - Avoid TSH <0.1mIU/L
    - Risk of thyrotoxicosis - A-fib and osteoporosis
  - Consider higher serum TSH target in elderly and hospitalized (eg. 8)

Repeat TSH q3-4 months until stable, then yearly
- If dose higher than expected, evaluate for GI disorder (H pylori gastritis, atrophic gastritis, celiac)
Follow serum TSH when started on medications, change in body weight, aging, pregnancy
Poor adherence, weekly levothyroxine should be considered

Altered mental status, hypoventilation, hypothermia, hypotension, bradycardia, hyponatremia, hypoglycemia
Treat aggressively (mortality 40%)
- Levothyroxine (T4) loading dose 200-400mcg IV, then 1.6mcg/kg/day IV
- Liothyronine (T3) 5-20mcg followed by 2.5-10mcg q8h given with T4
- Glucocorticoids (hydrocortisone 100mg IV q8-12h x2d) until coexisting adrenal insufficiency can be excluded
- Supportive measures (ventilation, fluids, correction of hyponatremia and hypothermia)

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