Thyroid diseases (hyper/hypothyroidism)

Thyroid Axis - The Control Tower

• Regulation: A classic negative feedback loop maintains hormonal balance.
• Hormones:
  • T4 (Thyroxine): Major circulating form; a prohormone.
  • T3 (Triiodothyronine): More potent, active form. Most T3 is formed from peripheral conversion of T4 by 5'-deiodinase.

⭐ Amiodarone & Iodine Effects: High iodine loads can induce hypothyroidism (Wolff-Chaikoff effect) or hyperthyroidism (Jod-Basedow phenomenon), especially in patients with underlying thyroid disease.

Hypothyroidism - The Slow Burn

• Etiology:

  • Hashimoto's Thyroiditis: Most common cause in iodine-sufficient regions; autoimmune destruction (Anti-TPO, Anti-Tg Abs).
  • Iatrogenic: Post-thyroidectomy, radioiodine therapy, or external radiation.
  • Drug-Induced: Amiodarone, lithium, checkpoint inhibitors.
  • Iodine Deficiency: Most common cause worldwide.

• Clinical Features: Generalized slowing of metabolism.

  • Systemic: Fatigue, weight gain, cold intolerance, constipation, ↓ DTRs.
  • Derm: Myxedema (non-pitting), dry/coarse skin, hair loss.
  • Cardiac: Bradycardia, ↓ cardiac output.

• Diagnosis:

  • Screen: ↑ TSH is the most sensitive marker.
  • Confirm: ↓ Free T4.

⭐ Myxedema Coma: A life-threatening state of severe hypothyroidism. Presents with altered mental status, hypothermia, bradycardia, and hypotension. Often precipitated by infection, cold exposure, or sedatives.

Hyperthyroidism - Full Throttle

• Pathophysiology: ↑ synthesis & secretion of thyroid hormone (T4/T3).
• Etiologies:
  • Graves' Disease: Most common. Autoimmune (Type II HSR) with TSH receptor-stimulating antibodies (TSI).
  • Toxic Multinodular Goiter: Multiple autonomous nodules.
  • Toxic Adenoma: Single autonomous nodule.
  • Thyroiditis: Transient release of preformed hormone (e.g., subacute de Quervain's).
• Clinical: Weight loss, heat intolerance, palpitations (AFib risk), anxiety, fine tremor, hyperreflexia, warm/moist skin, lid lag.
  • Graves' Triad: Hyperthyroidism, ophthalmopathy (exophthalmos), pretibial myxedema.
• Diagnosis: ↓ TSH, ↑ free T4/T3. Radioactive Iodine Uptake (RAIU) scan differentiates.

⭐ Thyroid Storm: A life-threatening thyrotoxicosis, often precipitated by stress (infection, surgery). Presents with fever, agitation, delirium, tachycardia, and arrhythmia. Requires urgent management with β-blockers, PTU, and steroids.

Thyroiditis & Emergencies - Code Red

• Thyroiditis Types

• Thyroid Storm (Thyrotoxic Crisis): Life-threatening hyperthyroidism (fever, delirium, tachycardia).

⭐ Thyroid Storm Tx Sequence: Always give Propylthiouracil (PTU) or Methimazole before iodine. Giving iodine first can transiently ↑ hormone synthesis (Jod-Basedow effect), worsening the storm.

• Myxedema Coma: Severe hypothyroidism → ↓ mental status, hypothermia, hypotension.

High‑Yield Points - ⚡ Biggest Takeaways

• Graves' disease is the most common cause of hyperthyroidism, driven by TSI antibodies, causing exophthalmos and pretibial myxedema.
• Hashimoto's thyroiditis, the most common cause of hypothyroidism, features anti-TPO antibodies and carries a risk of B-cell lymphoma.
• Subacute (de Quervain's) thyroiditis is a painful gland, typically following a viral URI.
• Thyroid storm and myxedema coma are life-threatening emergencies of hyper- and hypothyroidism, respectively.
• Riedel's thyroiditis presents as a rock-hard, painless goiter.