Thyroid Gland Diseases

Thyroid Basics & Goiters - Gland 101 & Lumps

• Thyroid 101: Butterfly-gland (C5-T1). Follicular cells: thyroglobulin → T4, T3. Parafollicular C-cells: calcitonin. Iodine essential; TSH (pituitary) controls synthesis/release.
• Key Tests: TSH (best initial), Free T4 (FT4), Thyroid Ultrasound (USG).
• Goiter: Thyroid gland enlargement.
  • Diffuse Non-Toxic: Simple (iodine deficiency), Colloid. Often euthyroid.
  • Multinodular Goiter (MNG): Most common type; multiple nodules. Usually euthyroid.
• Thyroid Nodule: Discrete lesion(s) within thyroid.

  ⭐ FNAC is the gold standard for evaluating thyroid nodules.

  • USG Malignancy Risks: Microcalcifications, marked hypoechogenicity, irregular margins, taller-than-wide shape, extrathyroidal extension.

Hypo & Hyperthyroidism - Energy Extremes

Hypothyroidism (↓ Energy)

• Definition: ↓ Thyroid hormone (TH) production.
• Causes: Hashimoto's, iodine deficiency, post-ablative, drugs (Li).
• Symptoms: Fatigue, weight gain, cold intolerance, constipation, bradycardia, myxedema. 📌 Mnemonic: "WITCH" (Weight gain, Intolerance to cold, Tiredness, Constipation, Hoarseness).
  • Children: Cretinism.
  • Severe: Myxedema coma.
• Labs: ↑ TSH, ↓ Free T4/T3.
• Rx: Levothyroxine.

Hyperthyroidism (↑ Energy)

• Definition: ↑ TH production.
• Causes: Graves' disease, toxic multinodular goiter (MNG), toxic adenoma.
• Symptoms: Weight loss, heat intolerance, palpitations, anxiety, tachycardia. 📌 Mnemonic: "SWIFT" (Sweating, Weight loss, Intolerance to heat, Fast heart rate, Tremor).
  • Graves': Exophthalmos, pretibial myxedema.
  • Severe: Thyroid storm.
• Labs: ↓ TSH, ↑ Free T4/T3.
• Rx: Anti-thyroid drugs (ATDs), radioiodine, surgery.

⭐ Hashimoto's thyroiditis (autoimmune destruction) is the most common cause of hypothyroidism in iodine-sufficient regions, while Graves' disease (TSH receptor antibodies) is the most common cause of hyperthyroidism.

Thyroiditis & Neoplasms Overview - Inflamed & Transformed

• Thyroiditis (Inflammation)
  • Hashimoto's Thyroiditis: Autoimmune; commonest hypothyroidism (iodine sufficient). Anti-TPO/Tg Abs. Histo: Lymphocytic infiltrate, Hurthle cells, germinal centers. ↑ B-cell NHL risk.
  • De Quervain's (Subacute Granulomatous): Post-viral URI. Painful goiter, fever, ↑ESR. Self-limiting: transient hyper→hypo→euthyroidism. Histo: Granulomatous inflammation.

    ⭐ De Quervain's (subacute granulomatous) thyroiditis is typically characterized by a painful thyroid and often follows a viral URI.

  • Riedel's Thyroiditis: Rare, extensive fibrosis ("woody" thyroid), mimics anaplastic carcinoma. Compressive symptoms. IgG4-related disease.
  • Subacute Lymphocytic (Painless/Silent): Painless/Silent. Often postpartum. Transient hyperthyroidism, may become hypothyroid. Lymphocytic infiltrate.
• Benign Neoplasms
  • Follicular Adenoma: Most common benign tumor. Solitary, encapsulated nodule. Usually non-functional ("cold" on scintigraphy). Crucial: no capsular/vascular invasion (vs carcinoma).

Malignant Thyroid Tumors - The Bad Actors

• Papillary Carcinoma (PTC): Most common (~85%).
  • Features: "Orphan Annie eye" nuclei (clear, grooved, inclusions), psammoma bodies.
  • Genetics: BRAF V600E, RET/PTC rearrangements.
  • Spread: Lymphatic. Prognosis: Excellent.
• Follicular Carcinoma (FTC): ~5-15%.
  • Differentiator: Capsular/vascular invasion (not just atypia).
  • Spread: Hematogenous (bone, lungs).
  • Genetics: RAS mutations, PAX8-PPARγ fusion.
• Medullary Carcinoma (MTC): ~3-5%.
  • Origin: Parafollicular C-cells; secretes calcitonin.
  • Stroma: Amyloid deposits (Congo red positive).
  • Genetics: RET proto-oncogene mutations (MEN 2A/2B).
• Anaplastic Carcinoma: <2%.
  • Highly aggressive, undifferentiated cells. Elderly patients.
  • Genetics: TP53, BRAF, TERT promoter mutations. Prognosis: Very poor.

⭐ Papillary carcinoma is the most common thyroid malignancy and is associated with "Orphan Annie eye" nuclei and psammoma bodies.

High‑Yield Points - ⚡ Biggest Takeaways

• Graves' disease: Most common hyperthyroidism cause; anti-TSH receptor Abs (TSI).
• Hashimoto's thyroiditis: Commonest hypothyroidism cause; anti-TPO/Tg Abs; ↑ risk B-cell lymphoma.
• Papillary carcinoma: Most common thyroid cancer; Orphan Annie eyes, psammoma bodies, BRAF mutation.
• Medullary carcinoma: From C-cells; ↑calcitonin; MEN2 (RET mutation).
• Subacute thyroiditis (de Quervain's): Painful gland, post-viral; transient hyperthyroidism.
• Riedel's thyroiditis: "Woody" or "rock-hard" thyroid due to extensive fibrosis.
• Cretinism: Neonatal hypothyroidism; impaired CNS & skeletal development.