Disorders of Calcium Metabolism Flashcards
PTH increases serum calcium by four ways: _________________.
increased bone resorption; increased intestinal absorption; decreased renal excretion; and increased renal resorption
What is the major storage form of vitamin D?
25-hydroxy vitamin D (in the liver)
What enzyme in the kidney activates vitamin D?
1-alpha hydroxylase
To assess for deficiency, we measure ________________.
the storage form of vitamin D
Vitamin D has a similar effect as parathyroid hormone. How do they differ?
Vitamin D increases phosphate levels, while PTH decreases phosphate levels
What are the two most common causes of hypercalcemia?
Primary hyperparathyroidism and malignancy (these account for 90% of hypercalcemias)
What are some less common causes of hypercalcemia?
Exogenous vitamin D toxicity Exogenous vitamin A toxicity Hyperthyroidism Granulomatous disease Thiazide diuretics Milk-alkali syndrome Immobilization Adrenal insufficiency Acute renal failure Familial hypocalciuric hypercalcemia
What is the first step in evaluating hypercalcemia?
Measure PTH: there are only two disorders where it’s high (primary hyperparathyroidism and familial hypercalcemia)
What are brown tumors?
They are overgrowths of osteoclasts that occur in response to extremely elevated levels of parathyroid hormone (such as from a parathyroid adenoma)
Most people with hyperparathyroidism have what symptoms?
None, most are asymptomatic
What might you see in a CBC of someone with hyperparathyroidism?
Anemia (because PTH suppresses erythropoiesis)
Someone with primary hyperparathyroidism might have lines in their joint spaces. What are these?
Chondocalcinosis
Most of the cases of hyperparathyroidism are ___________.
sporadic (10%)
MEN I is the disorder of three Ps: __________________.
pituitary adenoma, pancreatic endocrine tumors, and hyperParathyroidism
What is the genetic cause of MEN I?
Defects in the Menin gene (MEN1n… get it?)
Adenomas can be treated by _____________.
removing one gland –the affected gland
Parathyroid hyperplasia is treated by ______________.
removing three glands
What medical options can treat primary hyperparathyroidism?
Calcimimetics to decrease release of PTH
What three things can cause the release of PTH?
Decreased Ca
Increased PO4
Decreased vitamin D
Which three cancers are the most common cause of hypercalcemia due to malignancy?
Lung
Breast
Head and neck
What is the most common mediator of hypercalcemia from malignancy?
PTH-related peptide (PTH-RP)
How can you differentiate primary hyperparathyroidism and familial hypocalciuric hypercalcemia?
Measure 24-hour urine calcium. In a patient with FHH, it will be low.
What causes FHH?
Defects in the sensor regions of the calcium sensors.
There is only one cause of hypocalcemia that presents with low PTH. What is it?
Hypoparathyroidism
How do you correct calcium if albumin is low?
Add 0.8 [Ca] for every 1.0 unit of albumin below 4.0
Those with renal disease are deficient in ________________.
the active form of vitamin D
________________ usually presents with mucocutaneous candidiasis, low calcium, high phosphate, and low PTH.
Autoimmune hypoparathyroidism
What causes pseudohypoparathyroidism?
Defects in the signal transduction from the PTH receptor (thus, they actually present with high PTH!)
True or false: vitamin D promotes bone resorption.
True! At high levels vitamin D can stimulate osteoclasts.
What three cell types have CaSRs?
Parafollicular thyroid cells, parathyroid chief cells, and proximal renal tubule cells
Hyperparathyroidism is most often _______________.
asymptomatic
Many ____________ patients don’t need surgery.
primary hyperparathyroidism
What two lab criteria are diagnostic of secondary hyperparathyroidism?
- High PTH
- Low Ca, low vitamin D, or high phosphate
Hypoparathyroidism should be suspected when __________ is found in conjunction with ____________.
hypocalcemia; hyperphosphatemia
