Hypoparathyroidism
Summary
Hypoparathyroidism is a rare endocrine disorder characterized by low or inappropriately normal levels of Parathyroid Hormone (PTH), leading to Hypocalcaemia and Hyperphosphataemia. The most common cause in adults is Iatrogenic (damage during thyroid/parathyroid surgery). It is the only classic endocrine deficiency state where the missing hormone (PTH) is not routinely replaced, instead relying on active Vitamin D analogues. [1,2]
Clinical Pearls
The "Hungry Bone" Syndrome: After parathyroidectomy for Hyperparathyroidism, the sudden drop in PTH can cause severe, profound hypocalcaemia as the bones (starved of calcium for years) rapidly suck it up from the blood. This is distinct from permanent hypoparathyroidism but presents similarly acute.
Magnesium is the Key: Magnesium is required for PTH secretion and action. Severe Hypomagnesaemia (e.g., from PPIs or alcohol) causes a functional hypoparathyroidism that is resistant to Calcium replacement. Always check Mg in any hypocalcaemic patient.
Trousseau's Sign: More specific than Chvostek's (which is positive in 10% of normal people). Inflate the BP cuff > systolic pressure for 3 minutes. Look for Carpal Spasm (wrist flexion, MCP flexion, finger extension) - "Main d'accoucheur" (the hand of the obstetrician).
Causes
- Post-Surgical (75%): Accidental removal or devascularisation during Thyroidectomy/Parathyroidectomy. Can be transient (weeks) or permanent (>6 months).
- Autoimmune: Isolated or part of APS-1 (Autoimmune Polyglandular Syndrome Type 1).
- Genetic: DiGeorge Syndrome (22q11.2 deletion) - usually presents in childhood but can be missed.
- Infiltration: Wilson's disease, Iron overload (Haemochromatosis), Metastases.
- Functional: Severe Hypomagnesaemia.
Calcium Homeostasis
- Normal: Drop in Ca -> PTH Release -> Bone Resorption + Kidney Reabsorption + Gut Absorption (via Vit D).
- Hypoparathyroidism: This loop is broken. The gut and bone sources shut down. The kidney leaks calcium.
Biochemistry Profile
- Low Calcium.
- High Phosphate (Loss of PTH phosphaturic effect).
- Low PTH.
- Low 1,25-OH Vitamin D (Loss of renal activation).
| Condition | PTH | Phosphate | ALP |
|---|---|---|---|
| Hypoparathyroidism | Low | High | Normal |
| Vitamin D Deficiency | High | Low | High |
| CKD | High | High | High |
| Pseudohypoparathyroidism | High | High | Normal |
Symptoms (SPASMODIC)
Chronic Features
Biochemistry
- Calcium: Low (less than 2.2 mmol/L).
- Albumin: Check Adjusted Calcium.
- Phosphate: High (>1.4 mmol/L). This distinguishes it from Vit D deficiency where Phosphate is low.
- PTH: Low or Inappropriately Normal (e.g., 2.0 pmol/L when Ca is 1.8).
- Magnesium: Check to rule out functional cause.
- Urine Calcium: High (Hypercalciuria) - because PTH isn't there to reclaim it.
Other
- ECG: Prolonged QT interval (Torsades risk).
- CT Brain: Calcification of Basal Ganglia (Fahr's Syndrome).
Management Algorithm
HYPOCALCAEMIA PRESENT
↓
CHECK: PTH, Phos, Mg
↓
┌─────────────┼─────────────┐
ACUTE CHRONIC MAGNESIUM
(Tetany/Sz) (Stable) DEFICIENCY
↓ ↓ ↓
IV CALCIUM ORAL CALCIUM IV MAGNESIUM
GLUCONATE + ALFACALCIDOL SULPHATE
(10ml 10%) (Active Vit D) (Treat first)
1. Acute Hypocalcaemia (Emergency)
- IV Calcium Gluconate: 10ml of 10% solution over 10-20 mins.
- ECG monitoring essential.
- Correct Magnesium concurrently.
2. Chronic Management
- Oral Calcium: e.g., Adcal, Sandocal.
- Active Vitamin D: Alfacalcidol or Calcitriol.
- Why not Cholecalciferol (Plain Vit D)? Because the kidney needs PTH to activate the 1-alpha-hydroxylase enzyme to convert 25-OH-D to 1,25-OH-D. Without PTH, plain Vit D is ineffective.
- Recombinant PTH: (Natpar). Available in some countries for refractory cases but expensive.
3. Monitoring Goals
- Target: Maintain Calcium in the Low-Normal Range (e.g., 2.00 - 2.15 mmol/L).
- Why not normal?: In the absence of PTH, the kidney cannot reabsorb calcium. If you push serum calcium to normal/high, you cause massive Hypercalciuria -> Nephrocalcinosis -> Renal Failure.
- Calcium-Phosphate Product: Keep less than 4.4 to prevent soft tissue calcification.
- Renal Stones / Nephrocalcinosis: From hypercalciuria (Overtreatment).
- Cataracts: From hypocalcaemia.
- Basal Ganglia Calcification: Leading to movement disorders.
- Laryngospasm: Acute airway obstruction.
- Quality of Life: Many patients report "brain fog" and fatigue despite normal calcium.
- Recovery: 70% of post-surgical cases recover within 12 months.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Hypoparathyroidism | European Society of Endo (2015) | Target low-normal calcium. Monitor urine calcium annually. |
| Post-Thyroidectomy | BAETS | Protocol for post-op calcium checks. |
Landmark Evidence
1. REPLACE Study
- Showed efficacy of rhPTH(1-84) in reducing calcium/active vit D requirements, but long term safety/availability remains a discussion.
What is Hypoparathyroidism?
It is a condition where your parathyroid glands (four tiny glands in your neck behind the thyroid) produce too little hormone. This hormone controls the calcium level in your blood.
What caused it?
Usually, it happens after neck surgery (thyroid removal) if the glands were accidentally damaged or removed. Sometimes it is an immune system problem.
What are the symptoms?
Low calcium makes your nerves very twitchy. You might feel pins and needles in your lips or fingers, muscle cramps, or spasms in your hands.
How is it treated?
You will likely need to take calcium tablets and a special form of Vitamin D (Alfacalcidol) for life. You need regular blood tests to make sure the level isn't too low (cramps) or too high (kidney stones).
Primary Sources
- Bollerslev J, et al. European Society of Endocrinology Clinical Guideline: Treatment of chronic hypoparathyroidism in adults. Eur J Endocrinol. 2015.
- Shoback DM, et al. Presentation of Hypoparathyroidism: Etiologies and Clinical Features. J Clin Endocrinol Metab. 2016.
- Mannstadt M, et al. Efficacy and safety of recombinant human parathyroid hormone (1-84) in hypoparathyroidism (REPLACE). Lancet Diabetes Endocrinol. 2013.
Common Exam Questions
- Diagnosis: "Low Ca, High Phos, Low PTH?"
- Answer: Hypoparathyroidism.
- Pharmacology: "Which Vit D to use?"
- Answer: Alfacalcidol (1-alpha-hydroxylated).
- Sign: "Trousseau's sign method?"
- Answer: Inflate cuff > systolic BP for 3 mins.
- Target: "Treatment goal?"
- Answer: Low-Normal Calcium (Avoid Hypercalciuria).
Viva Points
- Fahr's Syndrome: Why does the brain calcify? High phosphate binds with calcium in the basal ganglia.
- Pseudohypoparathyroidism: What is it? Target organ resistance to PTH (Receptor mutation). Biochmemistry is same (Low Ca, High PO4, High PTH), but patient has short 4th/5th metacarpals and round face (Albright's Hereditary Osteodystrophy).
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.