Parathyroid

• 4 in number
• weighs 120 mg
• in close association with thyroid
• sometimes in mediastinum

Main function of PTH  is to control the level of ionized calcium in extracellular fluid

• Stimulates osteolysis by osteoclasts that release calcium and phosphate into extracellular fluid
• Increases renal tubular reabsorptiion of calcium and magnesium
• Decreases the renal tubular reabsorption of phosphate and bicarbonate. This helps to get rid of phosphate which tends to reduce ionized calcium
• Increases synthesis of vitamin D, enhancing intestinal absorption of calcium

Primary hyperparathyroidism

• Adenoma: (80-85%)  Autonomous
• Hyperplasia of all 4 glands
• Carcinoma
• Multiple endocrine neoplasia (Werner's syndrome, Sipple's syndrome)

Symptoms

• Asymptomatic 50% 
• Hypercalcemia
• Fatigue
• Coma
• Polyuria: failure of renal tubular concentrating ability
• Kidney stones
• Bone pain
• Pathological fractures

Signs

• Most of the time the tumor is not palpable
• Heterotropic calcification; Band keratopathy
• Dystrophic calcification
• Hypertension: Renal involvement

Lab

• Chemistry
• Elevated calcium
• Low serum phosphorous
• Elevated alkaline phosphatase
• Serum chloride is elevated
• Serum bicarbonate is reduced
• Elevated levels of immunoassay of PTH
• Urine
• Urinary calcium may be normal or elevated
• Specific gravity: loss of conentrating ability
• Radiology
• Subperiosteal resorption of cortex in phalanges
• Osteopenia
• Resorption of distal end of clavicles
• Salt and pepper mottling of skull
• EKG: Shortened PR interval with ventriculaar arrhythmias in severe hypercalcemia

Differential Diagnosis

• Hypercalcemia of malignancy
• Familial benign hypercalcemia
• Serum calcium in relatives
• Urine calcium decreased

Treatment

• Medical management and monitoring. 50%  identified on routine testing. Asymptomatic.
• Surgery
• Indications
• Surgical removal of abnormal gland/s
• Subtotal 3.5 glands parathyroidectomy in hyperplasia
• Hypercalcemia
• Increase urinary loss of calcium
• Hydration Urinary excretion of calcium tends to parallel that of sodium. Hence hydrate with normal saline. Increased glomerular filtration is followed by sodium induced renal calcium clearance at the loop.
• Furosemide: Inhibits Na absorption in the ascending loop of Henle. The increased Na in the distal tubule causes direct inhibition of calcium absorption. Excretion of potassium and magnesium occurs simultaneously and should be replaced.
• Decrease osteoclastic activity
• Calcitonin: Immediately decreases PTH-mediated bone resorption and also increases renal calcium clearance
• Bisphosphonates: Pamidronate: causes greater decreased PTH-mediated bone resorption than calcitonin with onset about 24-48 hours after use
• Mithramycin
• Dialysis: If severe associated with renal insufficiency this modality is useful to lower serum calcium,
• Post-op hypocalcemia
• Remaining parathyroid glands suppressed (transient hypoparathyroidism)
• Bone hunger in patients with osteitis fibrosa cystica
• Removal of all of parathyroid glands
• Pamidronate might continue to suppress bone resorption