Introduction

• Autonomous and excessive secretion of parathyroid hormone (PTH) → hypercalcemia.
• Cause: tumor of parathyroid gland, usually adenoma - rarely carcinoma.
• Signs: associated with subsequent hypercalcemia, ie polyuria, polydipsia.
• Diagnosis: laboratory data, imaging, histopathology.
• Treatment: parathyroidectomy.
• Prognosis: good following complete removal of affected parathyroid gland.

Pathogenesis

Predisposing factors

• Four parathyroid glands in two pairs in cervical area.
• The caudal pair are embedded in thyroid tissue.
• In normal animal PTH is secreted in response to low [serum calcium] and results in:
  • Reduced renal calcium excretion.
  • Increased renal phosphate excretion.
  • Increased renal vitamin D activation and subsequent increased intestinal calcium uptake.
  • Bone resorption, via activation of osteoclasts.
• Autonomous PTH secretion for an abnormal gland → hypercalcemia.

Pathophysiology

• Autonomous PTH secretion → hypercalcemia → clinical signs.

Timecourse

• Months.
• Animals often have long-term histories of vague illness.

Diagnosis

Treatment

Outcomes