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