Hypothyroidism Summary

Key Facts

  • Primary: 95% of cases (thyroid gland failure)
  • Secondary: Pituitary/hypothalamic dysfunction
  • Common in elderly women
  • Lifelong treatment required

Common Symptoms

  • Fatigue & lethargy
  • Cold intolerance
  • Weight gain
  • Dry skin/hair loss
  • Constipation

Diagnostic Tests

  • Primary: High TSH, low FT4
  • Subclinical: High TSH, normal FT4
  • Secondary: Low/normal TSH, low FT4
  • Check TPO antibodies

Treatment

  • Levothyroxine monotherapy
  • Start low, go slow in elderly/cardiac
  • Take on empty stomach
  • Lifelong therapy

Emergency - Myxedema Coma

  • Decreased mental status
  • Hypothermia
  • Hypotension
  • IV thyroid hormone + steroids

Hypothyroidism

Thyroid hormone deficiency - Diagnosis and Management

Overview

Hypothyroidism is a common condition of thyroid hormone (thyroxine [T4] and tri-iodothyronine [T3]) deficiency, which are essential for normal growth, development, and metabolism.

Causes

Primary Hypothyroidism

  • Iodine deficiency (commonest cause worldwide)
  • Autoimmune thyroiditis (Hashimoto's, atrophic thyroiditis)
  • Post-ablative therapy/surgery/radiotherapy
  • Drugs (amiodarone, lithium, interferon-alpha, etc.)
  • Transient thyroiditis (postpartum, subacute)
  • Thyroid infiltrative disease (sarcoidosis, amyloidosis)
  • Congenital hypothyroidism

Secondary Hypothyroidism

  • Pituitary/hypothalamic dysfunction due to:
    • Tumors (pituitary adenomas, gliomas)
    • Surgery, radiotherapy, or trauma
    • Pituitary infarction (Sheehan's syndrome)
    • Infiltrative disorders (amyloidosis, sarcoidosis)
    • Isolated TSH deficiency
    • Drugs (cocaine, dopamine, glucocorticoids)

Clinical Features

The symptoms and signs of hypothyroidism may be mild and non-specific, especially in the elderly. Suspect hypothyroidism with multiple features:

General Symptoms

  • Fatigue/lethargy
  • Cold intolerance
  • Weight gain
  • Constipation
  • Arthralgia/myalgia

Dermatological

  • Dry skin
  • Hair loss (lateral eyebrows)
  • Coarse dry hair
  • Periorbital edema

Cardiovascular

  • Bradycardia
  • Diastolic hypertension
  • Pericardial effusion

Neurological

  • Depression
  • Impaired memory
  • Carpal tunnel syndrome
  • Delayed reflexes

Reproductive

  • Menstrual irregularities
  • Infertility
  • Galactorrhea

Other Features

  • Goiter
  • Hoarse voice
  • Associated autoimmune diseases

Secondary Hypothyroidism Features

May include symptoms of primary hypothyroidism plus features of hypothalamic-pituitary disease: recurrent headache, diplopia, visual field defects, skin depigmentation, atrophic breasts, galactorrhoea, amenorrhoea, erectile dysfunction, loss of body hair, Cushing's syndrome, or acromegaly.

Diagnostic Classification

Primary Hypothyroidism

TSH: High (>10 mU/L)

FT4: Low

95% of cases

Subclinical Hypothyroidism

TSH: High

FT4: Normal

Often asymptomatic

Secondary Hypothyroidism

TSH: Low/Normal

FT4: Low

Pituitary/hypothalamic cause

Investigations

Thyroid Function Tests

Additional Tests

Imaging

Management of Primary Hypothyroidism

Levothyroxine Monotherapy

  • Starting dose: 1.6 mcg/kg/day (adults)
  • Elderly/cardiac: Start with 25-50 mcg/day
  • Administration: On empty stomach, 30-60 min before food
  • Monitoring: Check TSH after 6-8 weeks
  • Goal: TSH in reference range (0.4-4.0 mU/L)

Special Considerations

  • Pregnancy: Increase dose by 25-50%
  • Elderly: Start low, go slow to avoid cardiac complications
  • Cardiac disease: Monitor closely for angina/arrhythmias
  • Drug interactions: Calcium, iron, PPIs affect absorption

Myxedema Coma - Emergency Management

Clinical Presentation

Consider in any patient with coma/depressed mental status plus hypothermia, hyponatremia, and/or hypercapnia. Key clues: thyroidectomy scar or history of radioiodine therapy/hypothyroidism. Mortality remains high even with treatment.

Component Management
Thyroid Hormone
  • IV levothyroxine 200-400 mcg loading dose
  • Followed by 50-100 mcg daily
  • Consider adding IV liothyronine (T3)
  • GI absorption impaired - IV preferred
Glucocorticoids
  • Hydrocortisone IV 100 mg every 8 hours
  • Continue until adrenal insufficiency excluded
  • Do not wait for cortisol results
Supportive Care
  • Mechanical ventilation for respiratory failure
  • Passive rewarming for hypothermia
  • Correct hyponatremia cautiously
  • Vasopressors for refractory hypotension
  • Empiric antibiotics for suspected infection

Complications

Cardiovascular

  • Dyslipidemia
  • Metabolic syndrome
  • Coronary heart disease
  • Heart failure

Reproductive

  • Infertility
  • Pregnancy complications
  • Adverse neonatal outcomes

Neurological

  • Cognitive impairment
  • Sensory deficits

Myxedema Coma

  • Decreased mental status
  • Hypothermia
  • Hypotension
  • Hypoventilation