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Hypercalcemia and Hypocalcemia

Chapter 57 | Part 2: Cardinal Manifestations and Presentation of Diseases · Part 2 – Cardinal Manifestations & Presentation · Chapter 57

Key Clinical Points

  1. Corrected calcium formula: Add 0.8 mg/dL to total calcium for every 1.0 g/dL decrement in albumin below 4.0 g/dL; subtract 0.8 mg/dL for every 1.0 g/dL increase above 4.0 g/dL.
  2. PTH interpretation: In hypercalcemia, elevated or inappropriately normal PTH indicates primary hyperparathyroidism (pHPT); suppressed PTH indicates non-parathyroid causes (e.g., malignancy, granulomatous disease).
  3. FHH diagnosis: A calcium/creatinine clearance ratio < 0.01 is suggestive of familial hypocalciuric hypercalcemia (FHH), where parathyroid surgery is ineffective.
  4. Hypercalcemia treatment hierarchy: 1) Volume expansion with IV saline (4–6 L/24h); 2) IV aminobisphosphonates (Zoledronic acid 4 mg or Pamidronate 60–90 mg); 3) Calcitonin (4–8 IU/kg q6h) for rapid transient effect; 4) Denosumab for bisphosphonate-refractory cases.
  5. Vitamin D-mediated hypercalcemia: Treat with glucocorticoids (Hydrocortisone 200–400 mg daily or Prednisone 40–60 mg daily) to reduce intestinal absorption and 1,25(OH)D production.
  6. Hypocalcemia signs: Chvostek's sign (facial twitching) and Trousseau's sign (carpal spasm with BP cuff inflation) indicate neuromuscular irritability; QTc prolongation and Torsade de pointes risk in severe cases.
  7. Hypomagnesemia: Severe hypomagnesemia suppresses PTH release and can cause hypocalcemia; magnesium repletion is required before calcium correction.
  8. Denosumab dosing: 120 mg subcutaneously on days 1, 8, 15, and 29, then monthly; lower doses (0.3 mg/kg) for advanced kidney disease.
  9. Cinacalcet: Used for pHPT or hypercalcemia of malignancy driven by PTH; start 30 mg orally twice daily, titrated to normalize serum calcium.
  10. VITAMINS TRAP mnemonic provides a comprehensive differential for hypercalcemia (Vitamin D, Immobilization, Thyrotoxicosis, Thiazides, 24-hydroxylase deficiency, Addison's, Acromegaly, Acquired autoimmune, Milk-alkali, Inflammation, Neoplasia, Sarcoidosis, Tuberculosis, PTH, Paget's, Parenteral sources, Pheochromocytoma, Pregnancy-associated PTHrP, Pseudohypercalcemia).

1. DEFINITION & OVERVIEW

• Physiological Role: Calcium is essential for skeletal structure, cellular signaling, cardiac contractility, immune function, and neural signaling. • Homeostatic Range: Serum calcium is maintained in a narrow range of 8.5–10.5 mg/dL (2.1–2.6 mM). • Feedback Mechanism: ◦ Extracellular Ca2+ levels are stable (minutes–hours) due to feedback involving parathyroid hormone (PTH) and vitamin D. ◦ Low extracellular Ca2+ → activates Calcium-sensing receptor (CaSR) on parathyroid chief cells → increased PTH secretion. ◦ PTH actions: → Bone: Increases resorption of calcium. → Kidney: Increases distal renal tubule reabsorption and stimulates 1,25(OH)D production. ◦ Vitamin D action: 1,25(OH)D acts on the small intestine to increase dietary calcium absorption.

1.1 Calcium Homeostasis

• Dynamics: Intracellular calcium is highly dynamic (milliseconds); extracellular calcium is stable (minutes–hours). ◦ Homeostatic Loop: Low Ca2+ → ↑ PTH → ↑ Bone resorption + ↑ Renal reabsorption + ↑ 1,25(OH)D production → ↑ Gut absorption.

2. ETIOLOGY & PATHOPHYYSICOLOGY

• Hypercalcemia Overview: Primary hyperparathyroidism (pHPT) and malignancy are the two most common causes. ◦ pHPT: Usually a nonmalignant neoplasm (adenoma or hyperplasia) with impaired feedback inhibition by increased serum calcium. ◦ Malignancy: Often presents with an acute course; may involve PTHrP, lytic metastases, or excessive 1,25(OH)D production.

2.1 Causes of Hypercalcemia

• Excessive PTH Production: ◦ Primary hyperparathyroidism (sporadic/familial e.g., MEN). ◦ Tertiary hyperparathyroidism (long-term stimulation in renal insufficiency). ◦ Ectopic PTH secretion (very rare). ◦ FHH (mutations reducing CaSR signaling). ◦ Nongenetic alterations (lithium therapy, rare CaSR inhibitory autoantibodies). • Hypercalcemia of Malignancy: ◦ Overproduction of PTHrP (many solid tumors). ◦ Lytic skeletal metastases (breast, myeloma). ◦ Excessive 1,25(OH)D production (granulomatous diseases like sarcoidosis/TB; lymphomas). ◦ Vitamin D intoxication (excessive 25(OH)D or 1,25(OH)D; reduced catabolism via CYP24A1 deficiency). • Primary Increase in Bone Resorption: ◦ Hyperthyroidism, Paget's disease of bone, Immobilization. ◦ Ketogenic diet (rare), Milk-alkali syndrome, Total parenteral nutrition. • Other Causes: ◦ Endocrine disorders (adrenal insufficiency, pheochromocytoma, acromegaly, VIPoma). ◦ Medications (thiazides, vitamin A, lithium, foscarnet, teriparatide, aromatase inhibitors). ◦ Pseudohypercalcemia (e.g., calcium-binding IgM in Waldenström's macroglobulinemia).

2.2 Causes of Hypocalcemia

• Low Parathyroid Hormone Levels (Hypoparathyroidism): ◦ Parathyroid agenesis (genetic: GCM2 loss; X-linked mutations). ◦ Parathyroid destruction (Surgical, Autoimmune [e.g., APS-1], Radiation, Infiltration by sarcoid/IgG4-related disease). ◦ Reduced bioactive PTH secretion (Hypomagnesemia, severe hypermagnesemia, CaSR activating mutations). • High Parathyroid Hormone Levels (Secondary Hyperparathyroidism): ◦ Vitamin D deficiency (nutritional or renal-related). ◦ Malabsorption (Celiac, Crohn's, Short bowel syndrome). ◦ Excessive intravenous phosphate infusion. • Parathyroid Hormone Resistance: ◦ Pseudohypoparathyroidism (GNAS mutations). ◦ Congenital PTH receptor mutation syndromes. • Drugs & Miscellaneous: ◦ Alcohol (acute/chronic), Calcium chelators (citrate from blood products). ◦ Inhibitors of bone resorption (bisphosphonates, denosumab). ◦ Alkalosis (respiratory or metabolic) → increased calcium binding to albumin. ◦ Acute pancreatitis, Rhabdomyolysis, Refeeding syndrome.

3. CLINICAL FEATURES

• Hypercalcemia Severity: ◦ Mild (10.5–11.9 mg/dL): Often asymptomatic; may present with vague neuropsychiatric symptoms (concentration, mood). ◦ Moderate (≥12–14 mg/dL): Fatigue, proximal muscle weakness, constipation, hyporeflexia, nephrolithiasis. ◦ Severe (≥14 mg/dL): Progressively leads to lethargy, stupor, or coma; GI distress (nausea, vomiting, pancreatitis); acute renal failure. • Renal Impact: Hypercalcemia reduces renal concentrating ability by downregulating collecting duct aquaporin 2 → polyuria and volume depletion.

3.2 Hypocalcemia Symptoms

• Clinical Presentation: ◦ Mild/Chronic: Often asymptomatic. ◦ Moderate/Severe: Paresthesias (fingers, toes, perioral), neuromuscular irritability. ◦ Severe: Seizures, carpopedal spasm, bronchospasm, QTc prolongation → Torsade de pointes. • Physical Examination: ◦ Chvostek's sign: Facial twitching (perioral/zygomatic) upon facial nerve tapping. ◦ Trousseau's sign: Carpal spasm induced by BP cuff inflation to 20 mmHg above systolic for 3 min.

4. DIAGNOSTIC APPROACH

  1. Initial Step: Measure Total Serum Calcium and Albumin. ◦ Correct calculation: → If Albumin < 4.0 g/dL: Add 0.8 mg/dL for every 1.0 g/dL decrement. → If Albumin > 4.0 g/dL: Subtract 0.8 mg/dL for every 1.0 g/dL increment.
  2. PTH Interpretation: ◦ Elevated or Inappropriately Normal → Primary Hyperparathyroidism (pHPT). ◦ Suppressed → Non-parathyroid causes (Malignancy, Granulomatous disease, Vitamin D excess).
  3. FHH Screening: Calculate Calcium/Creatinine Clearance Ratio. → < 0.01 → Suggests Familial Hypocalciuric Hypercalcemia (FHH) [Surgery is ineffective].
  4. Additional Investigations: ◦ Serum Phosphate: Low in pHPT; High/Normal in Malignancy or Vitamin D excess. ◦ Serum 25(OH)D & 1,25(OH)D: Assess vitamin D status and identify granulomatous disease. ◦ Serum Magnesium: Essential to rule out hypomagnesemia as a cause of hypocalcemia.

Diagnostic Algorithm

  1. Correct Calcium (Albumin adjustment).
  2. Measure PTH → Determine if source is Parathyroid or Non-parathyroid.
  3. Assess Renal Function and Phosphate levels.
  4. Rule out FHH via Ca/Cr clearance ratio (< 0.01).
  5. Evaluate Vitamin D status (25(OH)D and 1,25(OH)D).

5. MANAGEMENT & TREATMENT

  1. Hypercalcemia Treatment Hierarchy: → Step 1: Volume expansion with IV saline (4–6 L/24h). → Step 2: IV aminobisphosphonates (Zoledronic acid 4 mg or Pamidronate 60–90 mg). → Step 3: Calcitonin (4–8 IU/kg q6h) for rapid transient effect. → Step 4: Denosumab for bisphosphonate-refractory cases.
  2. Vitamin D-mediated Hypercalcemia: → Treat with glucocorticoids (Hydrocortisone 200–400 mg daily or Prednisone 40–60 mg daily) to reduce intestinal absorption and 1,25(OH)D production.
  3. Hypocalcemia Management: → If PTH is suppressed → Treat underlying cause (e.g., hypoparathyroidism, hypomagnesemia). → If PTH is elevated → Address Vitamin D deficiency or malabsorption.
  4. Specialized Agents: → Cinacalcet: For pHPT or hypercalcemia of malignancy driven by PTH; start 30 mg orally twice daily, titrate to normalize serum calcium.

Denosumab Specifics

• Standard Dose: 120 mg subcutaneously on days 1, 8, 15, and 29, then monthly. • Renal Impairment: Lower dose (0.3 mg/kg) for advanced kidney disease.

6. KEY PEARLS & CLINICAL TRAPS

• VITAMINS TRAP Mnemonic: → Vitamin D, Immobilization, Thyrotoxicosis, Thiazides, 24-hydroxylase deficiency, Addison's, Acromegaly, Acquired autoimmune, Milk-alkali, Inflammation, Neoplasia, Sarcoidosis, Tuberculosis, PTH, Paget's, Parenteral sources, Pheochromocytoma, Pregnancy-associated PTHrP, Pseudohypercalcemia. • FHH Warning: Always check Ca/Cr clearance; if < 0.01, surgery is ineffective. • Hypomagnesemia Rule: Must replenish magnesium before attempting to correct calcium in hypocalcemia cases.

Clinical Pearls

• Acute vs Chronic: Malignancy usually presents acutely; pHPT/FHH present chronically. • Renal Impact: Hypercalcemia reduces renal concentrating ability via aquaporin 2 downregulation → polyuria and volume depletion.

Reference Tables

TABLE 57-1 Causes of Hypercalcemia Excessive PTH production

Harrison's 22e, p.362

  • Excessive PTH production
  • Primary hyperparathyroidism
  • Sporadic or familial (e.g., MEN) parathyroid adenoma or hyperplasia
  • Rarely parathyroid carcinoma
  • Tertiary hyperparathyroidism (long-term stimulation of PTH secretion in renal
    insufficiency)
  • Ectopic PTH secretion (very rare)
  • FHH (mutations reducing CaSR signaling)
  • Nongenetic alterations in CaSR function (lithium therapy, rare CaSR inhibitory
    autoantibodies)
  • Hypercalcemia of malignancy
  • Overproduction of PTHrP (many solid tumors)
  • Lytic skeletal metastases (breast, myeloma)
  • Excessive 1,25(OH)D production (by constitutive macrophage CYP27B1 activity)
    2
  • Granulomatous diseases (many causes: sarcoidosis, tuberculosis, leprosy,
    fungal infections, foreign body reaction)
  • Lymphomas (B cell, cutaneous T cell/Sezary syndrome)
  • Vitamin D intoxication
  • Ingestion of excessive vitamin D: 25(OH)D
  • Ingestion of excessive 1,25(OH)D (calcitriol) or 1-alpha-hydroxylated vitamin
    2
    D analogues
  • Reduced vitamin D catabolism due to CYP24A1 deficiency
  • Primary increase in bone resorption
  • Hyperthyroidism
  • Paget’s disease of bone
  • Immobilization
  • Ketogenic diet (in treatment of children with refractory epilepsy, uncommon)
  • Excessive calcium intake
  • Milk-alkali syndrome
  • Total parenteral nutrition
  • Other causes
  • Endocrine disorders (adrenal insufficiency, pheochromocytoma, acromegaly,
    VIPoma)
  • Medications (thiazides, vitamin A, lithium, foscarnet, teriparatide, aromatase
    inhibitors)
  • Discontinuation of denosumab with rebound resorption
  • Recovery phase of rhabdomyolysis with renal failure
  • Williams-Beuren syndrome
  • Excessive mammary PTHrP production with pregnancy or lactation (rare)
  • Pseudohypercalcemia (e.g., calcium-binding IgM in Waldenström’s
    macroglobulinemia)

TABLE 57-2 Causes of Hypocalcemia Low Parathyroid Hormone Levels (Hypoparathyroidism) Parathyroid agenesis

Harrison's 22e, p.363

  • Low Parathyroid Hormone Levels (Hypoparathyroidism)
  • Parathyroid agenesis
  • Isolated (genetic: autosomal recessive GCM2 loss of function; X-linked
    mutations)
  • Syndromic (e.g., DiGeorge’s, HDR, Kearns-Sayre)
  • Parathyroid destruction
  • Surgical
  • Autoimmune (genetic, e.g., APS-1; or acquired, including immune checkpoint
    inhibitors)
  • Radiation
  • Iron or copper overload (hemochromatosis, transfusion-dependent
    thalassemia, Wilson’s disease)
  • Infiltration by metastases or systemic diseases (sarcoid, IgG4-related disease,
    Riedel’s struma)
  • Reduced bioactive PTH secretion
  • Hypomagnesemia (genetic, drug-induced, anti–claudin-16 antibodies)
  • Severe hypermagnesemia (e.g., obstetric magnesium infusions)
  • Autosomal dominant hypocalcemia (CaSR activating mutations)
  • Autoimmune (CaSR activating antibodies; immune checkpoint inhibitor
    therapy)
  • Familial isolated hypoparathyroidism (rare PTH gene mutations)
  • High Parathyroid Hormone Levels (Secondary Hyperparathyroidism)
  • Vitamin D deficiency or impaired 1,25(OH)D production/action
    2
  • Nutritional vitamin D deficiency (poor intake or absorption)
  • Renal insufficiency [phosphate retention, impaired 1,25(OH)2D production]
  • Excessive intravenous phosphate infusion
  • Vitamin D resistance, including receptor defects
  • Intrinsic small intestine disorders with chronic calcium malabsorption
  • Roux-en-Y bariatric surgery, other causes of short bowel syndrome
  • Celiac disease, Crohn’s disease (often with concomitant vitamin D deficiency)
  • Parathyroid hormone resistance
  • Pseudohypoparathyroidism (GNAS mutations or imprinting defects)
  • Congenital PTH receptor mutation syndromes
  • PTH receptor blocking autoantibodies
  • Drugs
  • Alcohol (both acute and chronic ingestion)
  • Calcium chelators (including citrate from massive blood transfusion or FFP)
  • Inhibitors of bone resorption (bisphosphonates, denosumab, plicamycin)
  • Increased vitamin D catabolism (phenytoin, phenobarbital)
  • Phosphate-containing enemas (excessive or with renal disease)
  • Miscellaneous causes
  • Acute pancreatitis
  • Acute rhabdomyolysis
  • Hungry bone syndrome after parathyroidectomy
  • Osteoblastic metastases with marked stimulation of bone formation (prostate
    cancer)
  • Respiratory or metabolic alkalosis (increased calcium binding to albumin)
  • Refeeding syndrome and its management
  • Pseudohypocalcemia (e.g., low serum albumin with malnutrition, nephrotic
    syndrome, cirrhosis; gadoversetamide MRI contrast)