Calcium Metabolism Flashcards
1) Illustrate parathyroid hormone's effects on the kidney and GI tract 2) Identify the signs and symptoms of primary hyperparathyroidism 3) Distinguish primary hyperparathyroidism from familial hypocalciuric hypercalcemia 4) Recognize the negative consequences of hypoparathyroidism 5) Explain why vitamin D toxicity is not easily treated 6) Recalls the effects of vitamin D deficiency in children and adults
4 ways parathyroid hormone (PTH) increases serum calcium?
1) Increases bone resorption (activates osteoclasts).
2) Production of Active form of Vitamin D (adds 2 hydroxy groups)
3) Increased kidney reabsorption of Ca++.
4) Increased gut absorption of Ca++ (by calcitriol)
Mnemonic for hyperparathyroidism (hyper-PTH) effects?
What significant problem isn’t included in this mnemonic?
Bones, groans (GI stuff), stones, and psychic moans.
There is also kidney dysfunction (increase in urinary phosphate), and increased BP
Most common etiology of primary hyper-PTH?
Less common causes?
Solitary adenoma - 85%
Diffuse hyperplasia - 15%
Parathyroid carcinoma - <1% - really rare.
What happens to phosphate in hyper-PTH?
More is absorbed from bone, but even more is excreted in the kidney.
Net result: decreased serum phosphate (with decreased ECF phosphate).
2 GI effects of hyper-PTH?
1) Constipation, GI distress
2) Stomach ulcers, pancreatitis
What are the “psychic moans” of hyper-PTH?
Can cause depression and/or psychosis, fatigue and malaise.
Stones of hyper-PTH?
Kidney stones - from increased Ca++ in urine.
What’s the term for the pattern of bone demineralization seen in hyper-PTH? What 3 bone findings define it?
Osteitis fibrosa cystica.
1) Generalized demineralization of bone
2) Subperiosteal bone resorption
3) Bone cysts
What type of bone does hyper-PTH most effect? (What’s a good place to x-ray… or DXA??… that has a lot of this type of bone?)
Mostly affects cortical bone.
the distal radius is often looked at - femoral neck too. Not vertebrae.
How do most patients with hyper-PTH present?
With high Ca++ in screening bloodwork. They’re often caught before they’re symptomatic.
When would you do surgery on an asymptomatic patient with hyper-PTH? (there are 4 criteria)
When younger than 50.
Severe hypercalcemia.
Reduced creatinine clearance (impaired kidney function).
Osteoporosis.
(also want to make sure it’s not Familial Hypocalciuric Hypercalcemia)
- Only need to meet 1 of these criteria to go to surgery
Parathyroid adenoma looks histologically like…
increased cellularity… making lots of PTH.
- Clustering of cells–> can lead to atrophy of the parathyroid glands
3 causes of secondary hyper-PTH?
It’s all about decreased Ca++ due to…
1) Renal insufficiency.
2) Calcium malabsorption.
3) Vitamin D deficiency.
What is tertiary hyper-PTH?
Starts off as secondary PTH, but then some of the parathyroid becomes autonomous -> primary PTH.
What is Familial Hypocalciuric Hypercalcemia (FHH)? Sequelae?
There’s a mutation in the calcium sensor such that the set-point for PTH is shifted: PTH is secreted at a higher level of Ca++, so serum Ca++ stays higher than normal.
It’s a completely benign condition.
They have LOW URINE CALCIUM
DON”T SEND THEM TO SURGERY
Where is the mutated Ca++ sensor in FHH? Why does this matter?
In both the parathyroid and the kidney.
It matters that it’s in the kidney because excess Ca++ is NOT excreted into the urine because the kidney doesn’t think Ca++ is high.
Ca++ is kept at a higher set point both at the level of PTH and resorption in the kidney.
How do you differentiate primary hyper-PTH from FHH?
In primary hyper-PTH, urine Ca++ will be elevated (also causing kidney stones).
In FHH, urine Ca++ will be normal (low)
3 types of causes of hypoparathyroidism (hypo-PTH)?
1) Post-surgery following total thyroidectomy
2) Infiltrative disease.
3) Congenital.
2 infiltrative diseases that cause hypo-PTH?
Hemochromatosis, Wilson’s disease.
fine details…
2 congenital cause of hypo-PTH?
1) DiGeorge syndrome.
2) Autosomal recessive autoimmune polyglandular syndrome Type 1.
2 signs of hypocalcemia?
1) Cardiac arrhythmias.
2) Neuromuscular irritability. (paresthesias, tingling, tetany)
2 tetany signs associated with hypocalcemia? What is each?
Chvostek’s sign: tapping angle of jaw cause muscles innervated by the facial nerve to twitch.
Trousseau’s sign: carpal spasm (wrist flexion in response to prolonged brachial a. occlusion)
Tx for hypo-PTH?
Replace the downstream effects of PTH:
Give Ca++
Give Vitamin D.
What is the target calcium level for a patient with hypo-PTH? Why?
Low normal.
You’re not replacing PTH’s effect on kidney to reabsorb Ca++, so lots will spill into urine, and you don’t want to cause kidney stones.
