Hypoparathyroidism

Imaging Gallery

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Hypoparathyroidism is a disorder of insufficient parathyroid hormone (PTH) secretion, leading to hypocalcemia, hyperphosphatemia, and disrupted calcium homeostasis. Unlike the more common secondary hyperparathyroidism (elevated PTH from chronic hypocalcemia), hypoparathyroidism is characterized by inappropriately low or absent PTH in the setting of hypocalcemia.

Epidemiology:

• Prevalence: 70,000-90,000 cases in the United States (rare disorder)
• Post-surgical: 75% of cases are iatrogenic following thyroid or parathyroid surgery
• Permanent post-thyroidectomy: 1-2% of total thyroidectomies, higher after reoperative or central neck dissection (up to 10%)
• Autoimmune: 15-20% of cases, often part of polyglandular syndrome
• Genetic/congenital: 5-10%, includes DiGeorge syndrome

PTH Physiology Review

Normal PTH functions:

Net result of PTH deficiency: Low serum calcium, high serum phosphate, low urine calcium

Causes of Hypoparathyroidism

Pathophysiology of Hypocalcemia

Hypocalcemia mechanisms:

Hyperphosphatemia mechanism:

• PTH normally promotes renal phosphate excretion via inhibition of sodium-phosphate cotransporter in proximal tubule
• Absent PTH leads to phosphate retention
• High serum phosphate further suppresses 1-alpha hydroxylase (worsens vitamin D activation)

Neuromuscular effects:

• Ionized calcium is critical for normal neuron and muscle function
• Low calcium reduces action potential threshold (increased neuronal excitability)
• Results in tetany, seizures, and cardiac conduction abnormalities

Acute Hypocalcemia Presentation

Neuromuscular irritability (tetany):

• Carpopedal spasm: Most characteristic finding - wrist flexion with finger extension and thumb adduction (obstetrician hand position)
• Perioral paresthesias: Tingling or numbness around mouth and lips (often earliest symptom)
• Muscle cramps: Painful cramps in hands, feet, back, legs
• Laryngospasm: Sensation of throat tightness, stridor (high-pitched inspiratory sound)
• Seizures: Generalized tonic-clonic seizures without focal features

Cardiovascular:

• Prolonged QT interval: ECG shows QTc over 450 ms (males) or 470 ms (females)
• Heart failure: Rarely, severe chronic hypocalcemia causes dilated cardiomyopathy
• Arrhythmias: Torsades de pointes, ventricular tachycardia/fibrillation

Neuropsychiatric:

• Anxiety, irritability
• Depression
• Cognitive impairment, confusion
• Psychosis (rare)

Physical Examination Signs

Chronic Hypoparathyroidism Manifestations

Skeletal:

• Increased bone mineral density: Paradoxical finding (DEXA shows high T-scores)
• Reduced bone turnover: Low alkaline phosphatase, low bone formation markers
• Abnormal bone quality: Despite high density, may have impaired bone strength (static bone disease)

Neurological:

• Basal ganglia calcification: Present in 50% of chronic cases on CT brain
• Extrapyramidal symptoms: Parkinsonism (tremor, rigidity, bradykinesia), chorea, dystonia
• Papilledema: Rare, from increased intracranial pressure (pseudotumor cerebri)
• Seizures: Recurrent seizures if calcium not well controlled

Ophthalmologic:

• Cataracts: Subcapsular cataracts (posterior subcapsular) from chronic hypocalcemia
• Lens calcium deposition: Visible on slit lamp examination

Dental:

• Enamel hypoplasia: If hypoparathyroidism present during tooth development (childhood)
• Delayed tooth eruption: In congenital cases
• Dental caries: Increased risk

Dermatologic:

• Dry, coarse skin
• Brittle nails
• Hair loss (alopecia)

Biochemistry

Key diagnostic tests:

Serum calcium (total and ionized):

• Total calcium: Less than 2.0 mmol/L indicates hypocalcemia (normal 2.2-2.5)
• Ionized calcium: More accurate (not affected by albumin); less than 1.1 mmol/L is abnormal
• Correct for albumin: Corrected Ca = measured Ca + 0.02 x (40 - albumin in g/L)

Parathyroid hormone (PTH):

• Inappropriately low or undetectable in setting of hypocalcemia
• Normal PTH in hypocalcemia is inappropriate (should be elevated)
• Intact PTH assay is standard

Serum phosphate:

• Elevated (over 1.5 mmol/L; normal 0.8-1.5) due to lack of PTH-mediated renal excretion
• Hyperphosphatemia is characteristic of hypoparathyroidism

25-OH vitamin D:

• Usually normal in hypoparathyroidism (distinguishes from vitamin D deficiency)
• If low, suggests concurrent vitamin D deficiency requiring separate treatment

1,25-dihydroxy vitamin D (calcitriol):

• Low despite hypocalcemia (PTH normally stimulates 1-alpha hydroxylase)
• Not routinely measured but explains need for calcitriol supplementation

Magnesium:

• Must check - hypomagnesemia (less than 0.7 mmol/L) causes functional hypoparathyroidism
• Magnesium deficiency impairs PTH secretion and PTH action
• Correct magnesium before diagnosing true hypoparathyroidism

Alkaline phosphatase:

• Normal or low (reduced bone turnover, opposite of hyperparathyroidism)

24-hour urine calcium:

• Low (hypocalciuria) due to reduced filtered load despite reduced renal reabsorption
• Distinguishes from other causes of hypocalcemia

Electrocardiography

ECG findings:

• Prolonged QT interval (QTc over 450-470 ms) - most characteristic finding
• Prolonged ST segment: Increases QT duration
• T wave changes: May be flattened or inverted
• Arrhythmias: Torsades de pointes (polymorphic VT with prolonged QT), ventricular fibrillation

Imaging

CT brain (non-contrast):

• Basal ganglia calcification: Bilateral symmetric calcification of globus pallidus, putamen, caudate (50% of chronic cases)
• Dentate nuclei calcification: Cerebellar calcification
• Calcification correlates with duration and severity of hypocalcemia, not always symptomatic

DEXA bone density scan:

• Increased bone mineral density: Paradoxical finding (T-scores often +2 to +4 SD above normal)
• Z-scores more relevant (compare to age-matched controls)
• High density does not equal normal bone quality (low turnover state)

Parathyroid imaging (if etiology unclear):

• Ultrasound neck to assess for parathyroid tissue (may show atrophic or absent glands)
• Sestamibi scan not useful (requires functioning parathyroid tissue)

📊 Management Algorithm

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Acute Hypocalcemia Management

Chronic Hypoparathyroidism Management

Goals:

• Maintain serum calcium in low-normal range (2.0-2.2 mmol/L)
• Avoid hypercalciuria (keep urine calcium less than 300 mg/24hr)
• Prevent long-term complications (nephrolithiasis, nephrocalcinosis, basal ganglia calcification)
• Maintain quality of life

Calcium supplementation:

• Calcium carbonate: 1-3 g elemental calcium daily (divided doses with meals)
• Calcium citrate: Alternative if poor gastric acid (does not require acid for absorption)
• Titrate dose based on serum calcium and urine calcium

Activated vitamin D (essential):

• Calcitriol (1,25-dihydroxy vitamin D): 0.25-1 mcg twice daily
• Direct active form (bypasses need for PTH-mediated activation)
• More potent than cholecalciferol or ergocalciferol
• Risk of hypercalciuria (monitor 24-hour urine calcium)

Thiazide diuretics (adjunct):

• Hydrochlorothiazide: 25-50 mg daily
• Increases renal calcium reabsorption (reduces urine calcium)
• Useful if hypercalciuria develops despite dose optimization
• Caution: May cause hypokalemia, monitor electrolytes

Recombinant human PTH (rhPTH 1-84):

• Teriparatide or rhPTH 1-84: Subcutaneous injection
• Reserved for refractory cases not controlled on standard therapy
• Expensive, not widely available
• Improves calcium control and may reduce calcium/calcitriol requirements

Magnesium:

• Replace if deficient (oral magnesium oxide 400-800 mg daily)
• Necessary for PTH secretion and action

Monitoring schedule:

Preoperative Optimization

Preoperative assessment:

• Verify diagnosis: Review history, confirm on calcium/calcitriol replacement
• Check current calcium status: Serum total and ionized calcium, phosphate, magnesium
• ECG: Assess baseline QT interval (prolonged QT increases anesthetic risk)
• Medication review: Ensure patient taking medications, assess compliance
• Endocrinology consultation: For complex or poorly controlled cases

Medication management:

• Continue calcium and calcitriol on day of surgery if oral intake permitted
• If NPO prolonged (greater than 24 hours), may need IV calcium supplementation

Intraoperative Management

Monitoring:

• Continuous ECG monitoring for QT prolongation and arrhythmias
• Consider ionized calcium monitoring if prolonged case or significant fluid shifts
• Avoid rapid alkalosis (hyperventilation reduces ionized calcium by increasing protein binding)

Anesthetic considerations:

• Muscle relaxants: May have prolonged duration in hypocalcemia (monitor neuromuscular blockade)
• Citrated blood products: Large volume transfusion can chelate calcium (check ionized calcium)
• Hyperventilation: Avoid excessive hyperventilation (respiratory alkalosis decreases ionized calcium)

IV calcium availability:

• Have 10% calcium gluconate immediately available in OR
• If calcium drops or tetany/arrhythmia develops, give 10 mL IV calcium gluconate over 10 minutes

Postoperative Management

Monitoring:

• Check ionized calcium on arrival to recovery (especially if prolonged NPO or large fluid resuscitation)
• Continue cardiac monitoring if QT prolonged
• Resume oral calcium and calcitriol as soon as oral intake tolerated

Complications to watch for:

• Tetany: Carpopedal spasm, perioral numbness (check Trousseau/Chvostek signs)
• Seizures: Especially if calcium drops acutely
• Cardiac arrhythmias: Monitor for torsades de pointes if QT prolonged

IV to oral transition:

• If patient NPO prolonged postoperatively, may need IV calcium infusion temporarily
• Transition to oral once taking medications reliably
• Check calcium 24-48 hours after stopping IV calcium to ensure oral therapy adequate

Australian Epidemiology

Hypoparathyroidism in Australia follows similar epidemiological patterns to international data, with post-surgical causes (thyroidectomy, parathyroidectomy) accounting for approximately 75% of cases. The incidence of permanent hypoparathyroidism after total thyroidectomy is estimated at 1-2%, with higher rates in cases involving central neck dissection for thyroid malignancy.

Clinical Practice Considerations

Management of chronic hypoparathyroidism in Australia involves endocrinology specialist care for dose optimization of calcium and calcitriol. Patients are monitored with regular serum calcium measurements and periodic 24-hour urine calcium assessments to prevent nephrolithiasis. Recombinant PTH therapy is available through specialist centers for refractory cases but is not widely used due to cost and limited PBS subsidy.

Surgical Considerations

Australian guidelines emphasize the importance of parathyroid gland identification and preservation during thyroid and parathyroid surgery. Routine postoperative calcium monitoring is recommended for all patients undergoing total thyroidectomy, with supplementation initiated for symptomatic or biochemical hypocalcemia. Patients are counseled preoperatively about the risk of temporary versus permanent hypoparathyroidism.