Parathyroid Gland Disorders

Parathyroid Essentials - Calcium's Captains

• Typically 4 small glands, located posterior to the thyroid gland.
• Histology: Chief cells (synthesize & secrete PTH) and Oxyphil cells (function less clear, appear around puberty).
• Parathyroid Hormone (PTH): 84-amino acid peptide; primary regulator of calcium & phosphate balance.
• Net effect of PTH: ↑ serum $Ca^{2+}$, ↓ serum $PO_4^{3-}$.
• Key target organs:
  • Bone: ↑ osteoclastic activity, promoting $Ca^{2+}$ and $PO_4^{3-}$ release.
  • Kidney: ↑ $Ca^{2+}$ reabsorption (DCT), ↓ $PO_4^{3-}$ reabsorption (PCT), ↑ 1α-hydroxylase activity (converts 25-hydroxyvitamin D to active 1,25-dihydroxyvitamin D).
  • Intestine (indirect): Active Vitamin D enhances $Ca^{2+}$ and $PO_4^{3-}$ absorption.

⭐ Hypomagnesemia can impair PTH secretion and cause end-organ resistance to PTH, leading to hypocalcemia despite normal or even elevated PTH levels (functional hypoparathyroidism).

Hyperparathyroidism - HyperPTH Hijinks

• Types & Etiology:

  • Primary (PHPT): Most common. ↑PTH, ↑Ca.
    • Parathyroid Adenoma (~80-85%), Hyperplasia, Carcinoma.
  • Secondary: ↑PTH, normal/↓Ca.
    • Chronic Kidney Disease (CKD), Vitamin D deficiency.
  • Tertiary: Autonomous PTH secretion after prolonged secondary. ↑PTH, ↑Ca. Often post-renal transplant.

• Clinical Features: 📌 "Bones, stones, groans, moans."

  • Bones: Osteitis fibrosa cystica (brown tumors), bone pain, fractures, subperiosteal resorption (phalanges).
  • Stones: Recurrent nephrolithiasis, nephrocalcinosis.
  • Groans: Constipation, PUD, pancreatitis, nausea.
  • Moans: Fatigue, depression, confusion, weakness.

• Investigations:

  • Labs: ↑ Serum Ca, ↑ PTH (or inappropriately normal for ↑Ca), ↓ Serum PO₄ (in PHPT), ↑ ALP, ↑ 24hr Urine Ca.
  • Localization (for surgery in PHPT): Sestamibi scan, Ultrasound neck, 4D CT.

• Diagnostic Algorithm for Hypercalcemia:

• Management:
  • Primary: Parathyroidectomy (if symptomatic or meets criteria). Medical: Cinacalcet, Bisphosphonates.
  • Secondary: Treat underlying cause (e.g., Vit D, phosphate binders).
  • Tertiary: Parathyroidectomy.

⭐ Familial Hypocalciuric Hypercalcemia (FHH) is an important differential for PHPT, characterized by ↑Ca, ↑PTH, but ↓ urine calcium excretion (Urine Calcium/Creatinine Clearance Ratio < 0.01). It's usually benign and managed conservatively_

Hypoparathyroidism - HypoPTH Havoc

• Definition: Deficient parathyroid hormone (PTH) leading to hypocalcemia (↓ $Ca^{2+}$) & hyperphosphatemia (↑ $PO_4^{3-}$).
• Etiology:
  • Post-surgical (most common): Thyroid/parathyroid surgery.
  • Autoimmune (APS-1).
  • Congenital: DiGeorge syndrome (22q11.2 deletion).
  • Radiation, severe hypomagnesemia.
• Clinical Features (due to ↓ $Ca^{2+}$): 📌 CATS go numb:
  • Convulsions, seizures.
  • Arrhythmias (prolonged QT interval).
  • Tetany (neuromuscular irritability):
    • Chvostek's sign: Facial nerve tap → facial twitch.
    • Trousseau's sign: Cuff inflation → carpal spasm.
  • Spasms (laryngospasm), paresthesias (circumoral, digital).
  • Chronic: Cataracts, basal ganglia calcification.
• Investigations:
  • ↓ Serum $Ca^{2+}$ (total & ionized), ↑ Serum $PO_4^{3-}$, ↓ Serum PTH.
  • ECG: Prolonged QT interval.
• Management:
  • Acute (symptomatic): IV Calcium gluconate.
  • Chronic: Oral calcium, Vitamin D (calcitriol).

  ⭐ Pseudohypoparathyroidism (Albright's hereditary osteodystrophy) shows ↓ $Ca^{2+}$, ↑ $PO_4^{3-}$, but with ↑PTH (end-organ resistance), plus short 4th/5th metacarpals.

Surgical Aspects & MEN - Glandular Targets

• Indications: Symptomatic PHPT; Asymptomatic if: Age <50y, Ca >1mg/dL high, T-score < -2.5, CrCl <60 mL/min.
• Procedures: MIP (localized adenoma); BNE (MGD, failed localization).
• ioPTH: >50% drop, 10min post-excision (Miami criterion).
• MEN & Parathyroid:
  • MEN 1 (📌3Ps): Parathyroid (hyperplasia 90%), Pancreas, Pituitary.
  • MEN 2A: Parathyroid (adenoma/hyperplasia 20-30%), MTC, Pheo.

⭐ MEN 1: Parathyroid involvement is earliest & most common. oka

High‑Yield Points - ⚡ Biggest Takeaways

• Primary Hyperparathyroidism (PHPT): Caused mainly by parathyroid adenoma. Symptoms: "bones, stones, groans, moans".
• PHPT labs: ↑ Serum Calcium, ↑ PTH, ↓ Serum Phosphate.
• Secondary Hyperparathyroidism: Often due to CKD or Vitamin D deficiency.
• Hypoparathyroidism: Typically post-surgical; causes hypocalcemia (Chvostek's, Trousseau's signs).
• MEN 1 and MEN 2A syndromes frequently involve parathyroid tumors.
• Sestamibi scan: Gold standard for localizing parathyroid adenomas.
• Hungry Bone Syndrome: Severe post-parathyroidectomy hypocalcemia.