Hyporparathyroidism

Inadequate secretion or action of parathyroid hormone (PTH), leading to hypocalcemia, hyperphosphatemia, and altered neuromuscular excitability.

Aetiology

Most common cause

  • Post-surgical removal or injury of parathyroid glands (thyroidectomy, neck surgery)

Other causes

  1. Autoimmune destruction
  1. Congenital/Genetic
      • DiGeorge syndrome (22q11 deletion)
      • PTH gene mutations
  1. Infiltrative diseases
      • Hemochromatosis, Wilson disease
  1. Hypomagnesemia
      • Mg deficiency impairs PTH secretion & action
  1. Radiation exposure to neck
  1. Idiopathic

Pathophysiology

Functions of PTH

  • Activates osteoclasts - increased bone reabsoption, releases calcium
  • Increased reabsorption of calcium by renal tubules
  • Increased urinary phospate excretion
  • Increased synthesis of active forms of vitamin D

Regulation of PTH

  • Normally the above functions would increase serum calcium, so inhibit PTH secretion
  • PTH secretion is not terminated in hyperparathyroidism - continued osteoclasis

Hypoparathyroidism

🔻 Bone resorption → 🔻 serum Ca²⁺
🔻 Renal Ca²⁺ reabsorption → 🔻 Ca²⁺
🔺 Renal phosphate reabsorption → 🔺 PO₄³⁻
🔻 Calcitriol synthesis → 🔻 intestinal Ca²⁺ absorption
Result → hypocalcemia & hyperphosphatemia

Clinical Manifestation

Neuromuscular

  • Tetany
  • Muscle cramps/spasm
  • Paresthesias (around mouth, fingers, toes)
  • Carpopedal spasm
Signs
  • Chvostek sign: facial muscle twitch when tapping facial nerve
  • Trousseau sign: carpal spasm with BP cuff inflation

CNS

  • Seizures
  • Anxiety, irritability
  • Depression, confusion

Cardiovascular

  • Prolonged QT interval
  • Arrhythmias

Skin/Hair

  • Dry skin, brittle nails
  • Alopecia
  • Dental abnormalities (children)

Management

Acute hypocalcemic crisis

  • IV calcium gluconate
  • Cardiac monitoring required

Chronic management

  • Oral calcium supplements 1-2 gram in divided dosage
  • Vitamin D (Calcitriol 0.25-0.30 mcg/day preferred) to improve GI absorption
  • Thiazide diuretics to reduce urinary calcium loss
  • Maintain magnesium levels
  • Recombinant PTH therapy (Teriparatide) in refractory cases

Target levels

  • Maintain serum Ca²⁺ in low-normal range to avoid hypercalciuria