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(C) CM 1A: Heme/Onc/Endo > Lecture 19: PTH and Mineral Metabolism Disorders > Flashcards

Lecture 19: PTH and Mineral Metabolism Disorders Flashcards

1
Q

How is PTH secretion controlled via negative feedback?

A

Ionized calcium interacts with calcium sensing receptors (CaSRs) in the parathyroid and kidneys.
High calcium = suppressed PTH secretion.

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2
Q

In what 3 ways can the parathyroid increase its secretion of PTH in response to hypocalcemia?

A
  • Immediate: releasing preformed PTH.
  • Delayed: Expressing PTH mRNA
  • Extended: Parathyroid cell replication by increasing parathyroid gland mass
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3
Q

What are functions of calcium?

A
  • Maintain bone and teeth strength
  • Promote contraction and relaxation of muscle and blood vessels
  • Hormone and enzyme secretion
  • Neurocellular signaling
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4
Q

Where is calcium stored in the body?

A
  • 99% bone
  • Intracellular
  • Blood/ECF (50% of the Ca in this is bound to proteins)
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5
Q

What 3 organs control calcium levels?

A
  • SI/LI: absorbing dietary Ca
  • Kidneys: Reabsorbing Ca
  • Bones: Storing Ca
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6
Q

What secondary mineral has a similar profile to calcium in terms of storage and function?

A

Phosphate

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7
Q

What 3 hormones regulate the balance of calcium and phosphate?

A
  • PTH
  • Vit D-1,25
  • Calcitonin
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8
Q

What is the effect of PTH on the kidneys?

A
  • Reabsorb Ca
  • Excrete phosphate
  • Produce vit D-1,25
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9
Q

What is the effect of PTH on the bones?

A

Stimulates movement of Ca and phosphate from bone to the ECF.

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10
Q

What is the inactive form of Vit D-1,25?

A

Vit D-25

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11
Q

What is the function of Vit D-1,25?

A
  • Increasing intestinal absorption of dietary Ca and Phosphorus
  • Enhancing PTH effect on bone
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12
Q

What hormone opposes PTH? Where is it secreted from?

A

Calcitonin, secreted from C cells in the thyroid.

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13
Q

What triggers the release of calcitonin?

A

Hypercalcemia, overstimulating the C-cell receptors.

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14
Q

What does calcitonin do?

A
  • Suppresses renal absorption of Ca, increasing its excretion.
  • Inhibits osteoclastic activity, increasing bone calcium storage.
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15
Q

What makes up total calcium?

A

Protein bound and free Ca

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16
Q

What can falsely alter serum calcium concentrations?

A

Serum protein counts (esp. albumin)

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17
Q

When do I use a corrected calcium?

A

Patients with abnormal albumin levels or when ionized calcium levels are not available.

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18
Q

What lab test is used to diagnose hyperparathyroidism?

A

Serum PTH

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19
Q

What does increased serum PTH suggest?

A

Primary or secondary hyperparathyroidism.

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20
Q

What are the 2 forms of Vit D measured by a serum 25-hydroxy Vit D test?

A
  • D3 (cholecalciferol), synthesized in the epidermis
  • D2 (ergocalciferol), derived from plants.
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21
Q

What is the active form of vitamin D?

A

Calcitriol, aka 1,25-dihydroxy-Vit D

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22
Q

Disease of what organ can grossly affect Calcitriol levels?

A

Kidney.
Increased renal production in hyperparathyroidism.
Decreased levels with CKD.

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23
Q

What does an elevated serum phosphate suggest?

A

Hypoparathyroidism

Kidneys should be excreting it.

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24
Q

What is Parathyroid Hormone Related Protein (PTHrP)? Why is it significant?

A

Normally found in the body, but pathologically secreted by cancer cells.
Causes a PTH effect on the bone and kidney.

One of the top manifestations of paraneoplastic is hypercalcemia.

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25
What are the 2 main causes of hypercalcemia?
Hyperparathyroidism and malignancy
26
What are the clinical manifestations of hypercalcemia?
* Bones * Stones * Groans * Psychiatric Overtones
27
How do we treat severe hypercalcemia?
* IV NS w or w/o furosemide and corticosteroids.
28
What are the main causes of hypocalcemia?
Impaired PTH or Vit D production.
29
What causes low PTH and hypocalcemia?
* Parathyroid agenesis * Parathyroid destruction (surgery) * Reduced parathyroid function (hypomagnesemia) | Hypoparathyroidism
30
What causes high PTH but hypocalcemia?
* Vit D def * Tissue injury * PTH resistance * Drugs | Secondary hyperparathyroidism
31
What are the signs of hypocalcemia?
* Chvostek's * Trosseau's
32
What are the symptoms of hypocalcemia?
Paresthesias: fingers, toes, circumoral.
33
What labs should I order in initial eval of hypocalcemia?
* PTH level * Albumin, creatinine * Phosphorus, Mg * Vit D (both 25-hydroxy and 1,25-2D
34
What is the MCC of hypercalcemia?
Primary hyperparathyroidism: Excessive PTH secretion leading to hypercalcemia and hypophosphatemia. | MC in females aged 60-70.
35
What is the MCC of primary hyperparathyroidism?
Single parathyroid adenoma.
36
How does primary hyperparathyroidism typically present?
Asymptomatic, incidental finding on routine screenings.
37
When might a parathyroid mass be palpable? What symptoms does it show?
Only if it is a carcinoma (75% of the time) Symptoms are those of hypercalcemia.
38
What diagnoses primary hyperparathyroidism?
Elevated PTH. Generally elevates with size of adenoma, with carcinomas being > 14.0
39
How high is a parathyroid carcinoma's PTH level usually?
5x the ULN.
40
How do we differentiate between FHH and PHPT?
24 hour urine calcium collection. 200-300 excludes FHH. < 200 could be either. | FHH is hypocalciuric, so high calcium = unlikely.
41
How do we differentiate between PHPT and secondary?
Serum phosphate Low = PHPT High = Secondary dt CKD.
42
What should happen to serum 25-OH Vit D in PHPT?
Decreased due to excessive conversion.
43
When is imaging needed for PHPT?
* Neck US needed only if surgery is being considered. * Nuclear scan to check which tissue is hyperfunctioning. * CT-4D (if other scans are negative)
44
How is asymptomatic PHPT managed by a patient?
* Regular WEIGHT-bearing exercises * Avoid immobilization * Drinking adequate fluids. Avoid: * Thiazides * Large Vit A doses * Calcium antacids
45
What labs and imaging can we order to monitor asymptomatic PHPT?
* Serum Ca and Albumin 2x/yr * Renal function and urine calcium 1x/yr * Serum Vit D 25 * 3 site DEXA scan (distal radius, hip, and spine) every 2 yrs.
46
How do we manage symptomatic PHPT?
* Surgery (Recommended) * Cinacalcet (CaSR binder to decreasing PTH secretion) * Oral bisphosphonates (cannot treat hypercalcemia/uria) * IV bisphosphonates (can temp treat hypercalcemia)
47
What must a patient do when taking oral bisphosphonates?
Stand upright for 30 minutes after ingestion.
48
For postmenopausal women, what medication can help with PHPT?
Estrogen replacement, which causes slight reductions in serum calcium. | Raloxifene (agonist in bone, antagonist in breast/uterine tissue)
49
What are the main complications of PHPT?
* Osteopenia/Osteoporosis/Pathological fractures * Vit D def * Nephrolithiasis
50
What is secondary hyperparathyroidism?
Overproduction of PTH due to a chronic abnormal stimulus.
51
What is the MCC of secondary hyperparathyroidism?
* MCC: CKD * Second is Vit D def
52
What are the S/S of secondary hyperparathyroidism?
Hypocalcemia symptoms
53
What labs would I order to help evaluate secondary hyperparathyroidism?
* BUN/Cr (elevated in CKD) * PTH (high) * Ca (low-normal) * Phosphorus (high in CKD, low in Vit D def) * Vit D-1,25 (low in CKD)
54
How do we manage/treat secondary hyperparathyroidism?
Refer to nephro if CKD. Vit D supplementation if deficient
55
What is hypoparathyroidism and its etiologies?
Disorder of PTH deficiency. * Acquired s/p surgery * Autoimmune hypoparathyroidism * Parathyroid deficiency (irradiation, riedel thyroiditis, cancer) * Functional hypoparathyroidism (Severe hypomagnesemia or hypermagnesemia * Congenital (CaSR dysfunction)
56
What is the hallmark sign of acute hypocalcemia?
Tetany due to neuromuscular irritability
57
What signs and symptoms would I expect in hypocalcemia?
* Mild: Paresthesias * Severe: Spasms/seizures * Trousseau's * Chvostek's * Prolonged QT
58
How do lab tests typically appear for hypoparathyroidism?
* Serum calcium: LOW * Serum Phosphorus: HIGH * Urinary calcium: LOW * PTH: LOW * Vit D 1,25: LOW to NORMAL * Mg/Vit D-25, Creatinine: NORMAL * EKG: Prolonged QT and T wave abnormalities
59
What is the acute management protocol for hypoparathyroidism?
1. AIRWAY 2. IV Calcium gluconate 3. Oral Calcium 4. Magnesium (if hypomagnesemic) 5. Mg oxide after IV 6. Vit D therapy once oral calcium is started. (Calcitriol preferred)
60
What is the maintenance therapy for hypoparathyroidism?
* Oral calcium * Vit D supplements * Monitor Mg * Teriparatide SQ (if pt is refractory to Ca/Vit D)
61
When is a cryopreserved parathyroid tissue transplant indicated?
Patients undergoing parathyroidectomy. Usually placed into the forearm.
62
What requires more Vit D2, vit D deficiency or hypoparathyroidism?
Hypoparathyroidism requires 25x more at minimum with calcium supplements.
63
What is the difference between taking a Vit D2 supplement vs Calcitriol?
Calcitriol is the active form, requiring no conversion in the kidneys.
64
What are the indications for calcitriol?
* Hypocalcemia dt hypoparathyroidism * Secondary hyperparathyroidism with late stage CKD
65
When is calcium carbonate indicated?
* Hypocalcemia prevention/treatment. * Primary osteoporosis prevention.
66
When is calcium gluconate indicated?
Severe hypocalcemia.
67
What are the ARs of MgO supplementation?
Diarrhea and GI irritation

(C) CM 1A: Heme/Onc/Endo (28 decks)

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