Chapter 23 - Parathyroid Flashcards
Superior parathyroids derived from what?
4th pharyngeal pouch
Inferior parathyroids derived from what?
3rd pharyngeal pouch
Relation of superior parathyroids to surrounding structures?
Lateral to RLNs, posterior surface of superior portion of thyroid, above inferior thyroid artery
Relation of inferior parathyroids to surrounding structures?
Medial to RLNs, more anterior, below inferior thyroid artery
Most common ectopic location of inferior parathyroids?
Tail of the thymus; can migrate to the anterior mediastinum
Other ectopic sites of parathyroids?
Intrathyroid, mediastinal, near TE groove
What % of patients have all 4 glands?
90%
Blood supply to both superior and inferior parathyroids?
Inferior thyroid artery from thyrocervical trunk
Effects of PTH?
Increase serum Ca; increase kidney Ca reabsorpiton in distal convoluted tubule, decrease kidney PO4 absorption, increase osteoclasts in bone to release Ca and PO4, increase Vit D production in kidney
How does vitamin D increase Ca?
Increases intestinal Ca and PO4 absorption by increasing Ca-binding protein
Effects of calcitonin?
Decrease serum Ca; decrease bone Ca resorption (osteoclast inhibition), increase urinary Ca and PO4 excretion
Normal PTH level?
5-40 pg/mL
Most common cause of hypoparathyroidism?
Previous thyroid surgery
What oncogene increases the risk for parathyroid adenomas?
PRAD-1
What causes primary hyperparathyroidism?
Autonomously high PTH
How is the diagnosis of primary hyperparathyroidism made?
Increased Ca, decreased phos; Cl- to phos ratio >33, increased renal cAMP, HCO3- secreted in urine
Acid-base disorder seen with primary hyperparathyroidism?
Hyperchloremic metabolic acidosis
What is the bone lesion characteristic of primary hyperparathyroidism?
Osteitis fibrosa cystica (brown tumors)
Symptoms of primary hyperparathyroidism?
Muscle weakness, myalgia, nephrolithiasis, pancreatitis, PUD, depression, bone pain pathologic fractures, mental status changes, constipation, nausea and vomiting, anorexia
Indications for surgery for primary hyperparathyroidism?
Ca >13, decreased Cr clearance, kidney stones, substantially decreased bone mass
% of patients with single adenoma?
80%
% of patients with multiple adenomas?
4%
% of patients with diffuse hyperplasia?
15%; pts with MEN I or IIa have 4-gland hyperplasia
Treatment for parathyroid adenoma?
Resection; inspect other glands to r/o hyperplasia or multiple adenomas
Treatment for parathyroid hyperplasia?
Do not biopsy all glands (risk hemorrhage); resect 3.5 glands or total parathyroidecomy and autoimplantation
Treatment for parathyroid adenocarcinoma?
Radical parathyroidectomy (with ipsilateral thyroid)
Ideal time for operation in pregnant patient?
2nd trimester; increased risk of stillbirth if not resected
Why draw intra-op PTH levels?
Helps determine if causative gland is removed; PTH should go to <1/2 the preop value
What is the half-life of PTH?
3-4 minutes
What is the most common location of a gland that was unable to be found on initial operation?
Normal anatomic position
What is postop hypocalcemia caused by following parathyroidectomy?
Bone hunger, hypomagnesemia, failure of parathyroid remnant or graf
What is the most common cause of persistent hyperparathyroidism?
1%; due to missed adenoma
What causes recurrent hyperparathyroidsim?
New adenoma formation, tumor implants that have grown, recurrent parathyroid carcinoma
Bone hunger will show what lab values?
Normal PTH, decreased HCO3-
Aparathyroidism will show what lab values?
Decreased PTH, normal HCO3-
What is sestamibi-technetium-99 good for?
Preferential uptake by overactive parathyroid gland; good for picking up adenomas (not for hyperplasia); best for trying to pick up ectopic glands
What patients show secondary hyperparathyroidism?
Renal failure
Lab values in secondary hyperparathyroidism?
Increased PTH in response to decreased Ca
Treatment for secondary hyperparathyroidism?
Control diet PO4, PO4-binding gel, decreased aluminum, Ca supplement, vitamin D/Ca in dialysate
When is surgery indicated for secondary hyperparathyroidism?
Bone pain (80-90% get relief); total parathyroidecomy with autotransplantation
What is tertiary hyperparathyroidism?
Renal disease has been corrected with transplant, but still oerproduces PTH
Treatment of tertiary hyperparathyroidism?
Subtotal or total parathyroidectomy with autoimplantation
Lab values seen in familial hypercalcemic hypocalciuria?
High serum Ca, low urin Ca (should be high if hyperparathyroidism)
What is the cause of familial hypercalcemic hypocalciuria?
Defect in PTH receptor in distal convoluted tubule of kidney; causes increased resorption of Ca
Treatment for familial hypercalcemia hypocalciuria?
Nothing. Ca generally not that high; NO parathyroidectomy
What is pseudohypoparathyroidism caused be?
Defect in PTH receptor in kidney, does not respond to PTH
5-year survival for parathyroid cancer?
50% 5 year survival
Lab values in parathyroid cancer?
High Ca, PTH, and alkaline phosphatase
Most common site of mets from parathyroid cancer?
Lung
% of patients with parathyroid cancer recurrence?
50%
What are the tumors of MEN syndromes derived from?
APUD cells
Inheritance of MEN syndromes?
Autosomal dominant, 100% penetrance, variable expressivity
Tumors associated with MEN I?
Parathyroid hyperplasia (usually 1st to become symptomatic), pancreatic islet cell tumors, pituitary adenoma; correct hyperparathyroidism 1st
Tumors associated with MEN IIa?
Parathyroid hyperplasia, pheochromocytoma, medullary cancer of thyroid; correct pheo first
1 cause of death in MEN IIa/IIb?
Medullary thyroid cancer
Tumors associated with MEN IIb?
Pheochromocytoma, medullary cancer of thyroid, mucosal neuromas, Marfan’s habitus, musculoskeletal abnormalities
Gene mutation associated with MEN I?
MENIN gene
Gene mutation associated with MEN II?
RET proto-oncogene
Other causes of hypercalcemia?
Malignancy, hyperthyroidism, immobilization, granulomatous disease, excess vitamin D, milk-alkali syndrome, thiazide diuretics
MOA of midramycin?
Inhibits osteoclasts (used with malignancies or failure of conventional treatment); has hematologic, liver, renal side effects
What causes a hypercalcemic crisis? Treatment?
Usually secondary to another surgery; furosemide, dialysis
