Parathyroid Disorders: Hyperparathyroidism & Hypoparathyroidism – Anesthetic Relevance
I. Overview of Parathyroid Function
- The parathyroid glands (usually 4) are located posterior to the thyroid.
- They regulate calcium and phosphate homeostasis via parathyroid hormone (PTH).
Actions of PTH:
|
Organ |
Effect |
|
Bone |
Stimulates osteoclasts → ↑ bone resorption → ↑ Ca²⁺ |
|
Kidney |
↑ Ca²⁺ reabsorption, ↓ phosphate reabsorption, activates 1α-hydroxylase (vitamin D activation) |
|
Gut (via calcitriol) |
↑ Ca²⁺ and phosphate absorption |
Normal Calcium Physiology
- Total serum calcium: 8.5–10.5 mg/dL
- Ionized (free): ~50% (active form) → normal: 1.1–1.3 mmol/L
- Protein-bound (mostly to albumin): ~40%
- Complexed (with phosphate, citrate): ~10%
📌 Only ionized calcium is physiologically active – important for muscle contraction, nerve conduction, coagulation, enzyme function.
Factors Influencing Calcium Levels
- pH: Alkalosis → more calcium binds to albumin → ↓ ionized Ca²⁺
- Albumin: Low albumin → low total Ca²⁺ but normal ionized Ca²⁺
- Citrate (e.g., in massive transfusion): Binds calcium → hypocalcemia
- Magnesium: Deficiency → impairs PTH → secondary hypocalcemia
II. Hyperparathyroidism (HPT)
A. Types
|
Type |
Features |
|
Primary HPT |
Parathyroid adenoma (85%), hyperplasia, carcinoma |
|
Secondary HPT |
CKD → ↓ calcitriol & chronic hypocalcemia → ↑ PTH |
|
Tertiary HPT |
Long-standing secondary HPT → autonomous PTH secretion |
B. Clinical Features
- Bones – Bone pain, fractures (osteitis fibrosa cystica)
- Stones – Nephrolithiasis, nephrocalcinosis
- Groans – Abdominal pain, pancreatitis, peptic ulcers, constipation
- Moans – Fatigue, depression, cognitive dysfunction
- Short QT interval on ECG
C. Investigations
- ↑ Serum Ca²⁺ (ionized and total)
- ↓ Serum phosphate
- ↑ PTH
- Elevated alkaline phosphatase (with bone turnover)
- Imaging: Sestamibi scan, USG, 4D-CT (for localization)
III. Hypoparathyroidism
A. Causes
|
Type |
Causes |
|
Postsurgical |
Most common: post-thyroidectomy/parathyroidectomy |
|
Autoimmune |
Autoimmune polyglandular syndromes |
|
Genetic |
DiGeorge syndrome, familial |
|
Other |
Radiation, infiltrative diseases (hemochromatosis, Wilson’s) |
B. Clinical Features
- Neuromuscular excitability: Tetany, cramps, perioral numbness, carpopedal spasm
- Chvostek’s sign, Trousseau’s sign
- Laryngospasm, seizures
- QT prolongation → arrhythmias
- Cataracts, dry skin, brittle nails (chronic cases)
C. Labs
- ↓ Total and ionized Ca²⁺
- ↑ Serum phosphate
- ↓ or inappropriately normal PTH
- Normal to low magnesium
IV. 🔶 Anesthetic Implications of Parathyroid Disorders
A. Preoperative Evaluation
🔹 Hyperparathyroidism
- Correct hypercalcemia (hydrate, loop diuretics, bisphosphonates)
- Evaluate renal function (stones, nephrocalcinosis)
- Assess bone status, fractures
- Baseline ECG (QT shortening, arrhythmias)
- Check electrolytes (Ca²⁺, Mg²⁺, phosphate)
🔹 Hypoparathyroidism
- Correct hypocalcemia, magnesium
- Evaluate for seizures, laryngospasm, prolonged QT
- Avoid alkalosis (↓ ionized Ca²⁺)
- Ensure recent labs: ionized Ca²⁺, phosphate, Mg²⁺
B. Intraoperative Management
|
Concern |
Hyperparathyroidism |
Hypoparathyroidism |
|
Airway |
Possible difficult airway in MEN syndrome or hyperplasia |
Risk of laryngospasm |
|
Fluid management |
Hydration crucial |
Care with fluids to prevent dilutional hypocalcemia |
|
Calcium status |
Monitor ionized Ca²⁺ continuously if possible |
Continuous monitoring required |
|
Arrhythmias |
Short QT, brady- or tachyarrhythmias |
Prolonged QT, torsades risk |
|
Neuromuscular blockade |
↓ sensitivity to NMBs |
↑ sensitivity to NMBs |
|
Transfusions |
Citrate in PRBCs chelates calcium → worse hypocalcemia |
Can precipitate tetany; Ca²⁺ supplementation needed |
|
Ventilation |
Avoid hyperventilation (alkalosis ↓ ionized Ca²⁺) |
Same; maintain normocapnia |
|
ECG Monitoring |
QT interval shortening |
QT prolongation |
|
Cardiac Contractility |
Increases initially |
Decreases |
|
Other |
↓ Coagulation (impaired clotting cascade) |
Nephrogenic DI |
C. Postoperative Considerations
🔹 Post-Parathyroidectomy
- “Hungry bone syndrome”: Sudden drop in Ca²⁺ due to bone remineralization
→ Symptoms: hypocalcemia, tetany, arrhythmias
→ Management: aggressive calcium and vitamin D supplementation - Monitor for laryngospasm, seizures
- Observe for hypomagnesemia, hypophosphatemia
🔹 Hypoparathyroid Patients
- Continue oral calcium, calcitriol
- ICU monitoring for unstable ionized calcium
- Watch for respiratory complications (e.g., laryngospasm)
VI. Viva/MCQ Pearls
- Most common cause of hypoparathyroidism: Post-surgical
- Classic sign of acute hypocalcemia: Trousseau’s sign
- Calcium level at which tetany occurs: Ionized Ca²⁺ < 0.9 mmol/L
- Hungry bone syndrome: Post-parathyroidectomy hypocalcemia
- QT interval in hypercalcemia: Shortened
- PTH effect on phosphate: ↓ due to renal excretion
- Calcium gluconate vs. calcium chloride: Gluconate preferred for peripheral IV