Canis ISSN: 2398-2942

Primary hypoparathyroidism

Introduction

• Relatively rare.
• Cause: immune-mediated degenerative or surgical removal of glands.
• Signs: characterized by hypocalcemia + hyperphosphatemia and either transient or permanent PTH insufficiency.
• Eclampsia in late pregnancy or lactation Puerperal tetany.
• Diagnosis: biochemistry.
• Treatment: calcium and vitamin D supplementation.
• Prognosis: fair to good with treatment.

Pathogenesis

Etiology

• Spontaneous:
  • Agenesis of parathyroid glands.
  • Atrophy of parathyroid glands with prolonged hypercalcemia Hypercalcemia: overview.
  • Immune-mediated parathyroiditis.
  • Idiopathic: rare ? familial in St. Bernard (may be associated with hypothyroidism Hypothyroidism ).
• Complication of thyroidectomy: removal of, or damage to, parathyroids.
  One parathyroid gland is sufficient to prevent occurrence of tetany.

Pathophysiology

• In normal animal release of parathyroid hormone (PTH) from the parathyroid gand is stimulated by a drop in ionized calcium levels.
• PTH increases serum ionized calcium by increasing:
  • Calcium resorption from glomerular filtrate.
  • Phosphate secretion.
  • Osteoclast function thereby increasing bone resorption.
  • Vitamin D formation.
• Reduced PTH secretion → decreased serum ionized calcium → increased neuromuscular irritability → tetany and convulsions.
• Excessive panting and hyperventilation during tetany can → respiratory alkalosis → increased protein-bound calcium and reduced ionized calcium → exacerbation of problem.
• Pyrexia may be due to increased muscle activity during tetanic spasm.

Timecourse

• Within days or months of thyroidectomy.
• May be temporary or permanent.

Diagnosis

Treatment

Outcomes