Parathyroid Disorders

Anatomy & Physiology - Tiny Glands, Big Impact

• Typically 4 glands, posterior to thyroid; ectopic sites common.
• Blood: Mainly inferior thyroid artery.
• Cells: Chief cells (PTH secretion); Oxyphil cells.
• PTH: Regulates $Ca^{2+}$/$PO_4^{3-}$ homeostasis.
  • Trigger: ↓ Serum $Ca^{2+}$.
  • Actions: ↑ Bone resorption; Kidney: ↑ $Ca^{2+}$ reabsorb, ↓ $PO_4^{3-}$ reabsorb, ↑ Vit D active.
  • Result: ↑ Serum $Ca^{2+}$, ↓ Serum $PO_4^{3-}$.

⭐ PTH enhances calcium reabsorption mainly in the kidney's Distal Convoluted Tubule (DCT).

Hyperparathyroidism - Calcium Chaos Creators

• Excess PTH secretion leading to ↑ serum $Ca^{2+}$.

• Types & Etiology:

  • Primary: Adenoma (~85%), hyperplasia, carcinoma.
  • Secondary: CKD (most common), Vit D deficiency.
  • Tertiary: Autonomous PTH after chronic secondary.

• Clinical Features: 📌 "Stones, Bones, Groans, Moans, Psychic Overtones"

  • Stones: Renal ($Ca^{2+}$).
  • Bones: Osteitis fibrosa cystica (OFC, brown tumors), subperiosteal resorption, pain.
  • Groans: Abdominal pain, PUD, pancreatitis.
  • Moans/Psychic: Fatigue, depression, confusion.

• Investigations:

  • Labs: ↑PTH, ↑$Ca^{2+}$, ↓$PO_4^{3-}$, ↑ALP, ↑urine cAMP.
  • Imaging: Sestamibi, USG neck. X-ray: subperiosteal resorption (phalanges), 'salt & pepper' skull.

• Management:

  • Primary: Parathyroidectomy (symptomatic; or asymptomatic if: Age <50y, Serum $Ca^{2+}$ >1mg/dL above ULN, BMD T-score ≤-2.5, CrCl <60mL/min, Urine $Ca^{2+}$ >400mg/d). Medical: Cinacalcet.
  • Secondary/Tertiary: Treat cause / Parathyroidectomy.

⭐ Subperiosteal bone resorption, especially of the radial aspects of the middle phalanges, is pathognomonic for hyperparathyroidism.

Hypoparathyroidism - Calcium Calamity

• ↓PTH → ↓Serum $Ca^{2+}$, ↑Serum $PO_4^{3-}$.
• Etiology:
  • Most common: Post-surgical (thyroid/parathyroid surgery).
  • Autoimmune, DiGeorge syndrome (22q11.2 deletion).
  • Severe hypomagnesemia (functional).
• Clinical Features (Hypocalcemia):
  • Neuromuscular: Tetany (Chvostek's, Trousseau's signs), paresthesias, muscle cramps, seizures.
    • 📌 Mnemonic: "CATS go numb" (Convulsions, Arrhythmias, Tetany, Spasms).
  • ECG: Prolonged QT interval.
  • Chronic: Cataracts, basal ganglia calcification.
• Diagnosis: ↓Serum $Ca^{2+}$ (< 8.5 mg/dL), ↑Serum $PO_4^{3-}$, ↓PTH.
• Management:
  • Acute: IV Calcium gluconate.
  • Chronic: Oral calcium, Vitamin D (Calcitriol).

⭐ The most common cause of hypoparathyroidism is iatrogenic, following anterior neck surgery (e.g., thyroidectomy).

Diagnostics & Surgery - Scalpels & Scans

• Biochemical Diagnosis:
  • ↑ Serum Ca (Total & Ionized), ↓ Serum Phosphate, ↑ PTH.
  • ↑ 24-hr Urinary Ca, ↑ ALP (bone isoenzyme).
  • Assess Vitamin D levels (rule out secondary HPT).
• Localization Studies (Pre-operative):
  • Sestamibi Scan (Tc-99m): Primary modality; SPECT/CT enhances accuracy.

    ⭐ Sestamibi scan is the gold standard for preoperative localization of parathyroid adenomas, especially with SPECT/CT.

  • Ultrasound Neck: Good for cervical glands, guides FNA; operator-dependent.
  • 4D CT Scan: High resolution; for ectopic glands, reoperations.
  • MRI: Alternative if others inconclusive/contraindicated.
• Surgery (Parathyroidectomy): Definitive treatment.
  • Indications (Asymptomatic Primary HPT):
    • Serum Ca > 1 mg/dL above upper limit of normal.
    • Bone: T-score < -2.5 (osteoporosis) or fragility fracture.
    • Renal: CrCl < 60 mL/min or 24-hr urine Ca > 400 mg/day / nephrolithiasis.
    • Age < 50 years.
  • Surgical Approaches:
    • Minimally Invasive Parathyroidectomy (MIP): For pre-operatively localized single adenoma.
    • Bilateral Neck Exploration (BNE): If localization fails or multiglandular disease suspected.
  • Intraoperative PTH (IOPTH) Monitoring: Miami criterion: >50% drop from baseline 10 min post-excision confirms successful removal.

High‑Yield Points - ⚡ Biggest Takeaways

• Primary HPT: Most often parathyroid adenoma; causes hypercalcemia, hypophosphatemia, ↑PTH.
• Secondary HPT: Usually from CKD; features hypocalcemia/normal Ca, hyperphosphatemia, ↑PTH.
• Tertiary HPT: Autonomous PTH secretion after long-standing secondary HPT; leads to hypercalcemia.
• FHH: CaSR gene mutation; mild hypercalcemia, low urine calcium. Differentiate from primary HPT.
• Sestamibi scan: Key for localizing adenomas. Intraoperative PTH confirms removal.
• Hungry Bone Syndrome: Post-op hypocalcemia due to rapid bone uptake.
• MEN syndromes: Associate parathyroid issues with MEN 1 and MEN 2A.