| Introduction |
- Causes of hypocalcemia include
- decreased PTH that can be caused by
- hypoparathyrodism
- pseudohypoparathyroidism
- renal osteodystrophy
- decreased vitamin D3
|
| Presentation |
- Symptom
- symptoms of hypocalcemia
- paresthesia
- fingertip, toes, perioral
- abdominal pain, biliary colic
- muscle cramps, tetany
- dyspnea (laryngospasm, bronchospasm)
- convulsions
- mental status changes
- anxiety, fatigue, mood swings
- Physical exam
- findings of tetany
- Trousseau's Sign
- carpopedal spasm after blood pressure readings
- inflate BP cuff 20mmHg above systolic BP x 3-5min
- hand adopts a MCP flexed, DIP and PIP extended position
- more sensitive than Chvostek's sign
- Chvostek's Sign
- facial muscle contractions after tapping on the facial nerve
- dermatologic
- fungal nail infections
- hair loss
- blotchy skin
|
| Radiographs |
- Basal ganglia calcification
- comprises striatum, globus pallidus, substantia nigra, subthalamic nucleus
|
| Evaluation |
- Serum calcium, phosphate, vit D, PTH
- Serum albumin
- low serum albumin (low protein) leads to low total calcium
- but ionized calcium levels will be normal
- pH
- alkalosis increases albumin binding to ionized calcium
- EKG
- prolonged QT interval
|
| |
Serum Ca
|
Serum Phos |
PTH |
Common Cause |
| Hyperparathyroidism |
↑
|
↓
|
↑
|
adenoma |
| Hypoparathyroidism |
↓
|
↑
|
↓
|
parathyroidectomy |
| Ectopic PTH |
↑
|
↓
|
↓
|
malignancy |
| Vit D malabsorption |
↓
|
↓
|
↑
|
celiac disease, other GI isease |
| hypo vit D with no phosphate excretion from the kidney. |
↓
|
↑
|
↑
|
renal failure, pseudo
hypoparathyroidism |
|
| Pseudohypoparathyroidism (PHP) |
- Rare genetic disorder
- Mechanism
- PTH resistance
- decreased target cell response to PTH
- Laboratory
- high PTH
- low calcium
- high phosphate
- low vit D
- Types
- type 1a - Albright hereditary osteodystrophy
- defect in GNAS1 (Gsα protein)
- defective gene from mother
- upstream defect
- proximal to formation of cAMP
- skeletal defects
- short 4th, and 5th metacarpals and metatarsals or short 4th metacarpal only
- "knuckle, knuckle, dimple, dimple" sign on closed fist
- differentials
- Turner syndrome
- short 4th metacarpal only
- "knuckle, knuckle, dimple, knuckle"
- Down syndrome
- brachydactyly
- exostoses
- round facies
- obesity
- short stature
- diminished intelligence
- type 1b
- defect in GNAS1 (Gsα protein)
- normal appearance
- type 2
- unknown gene defect
- downstream defect
- distal to formation of cAMP
- normal appearance
- differentiate type 1 and type 2 by administering exogenous PTH (Ellsworth-Howard test)
- Type 1 - no increase in urinary cAMP and phosphate
- Type 2 - increased excretion of urinary cAMP and phosphate
|
| Pseudopseudohypoparathyroidism (pseudo-PHP) |
- Mechanism
- No PTH resistance
- normal target cell response to PTH
- Genetics
- defect in GNAS1 (Gsα protein)
- defective gene from father
- Skeletal defects
- also has short 4th metacarpal and metatarsal
- metastatic calcification
- Laboratory
- normal PTH
- normal calcium
- normal phosphate
- normal vit D
|
| |
Appearance |
PTH
|
Calcium |
Phos |
Vit D |
Response to PTH administration |
Genetics |
| Hypoparathyroidism |
Normal |
↓
|
↓ |
↑
|
↓
|
- |
- |
Pseudohypoparathyroidism Type 1a
|
Skeletal defects |
↑
|
↓ |
↑
|
↓
|
no increase in urinary cAMP or phosphate |
GNAS1 (maternal defect, upstream)
|
| Pseudohypoparathyroidism Type 1b |
Normal |
↑
|
↓ |
↑
|
↓
|
|
GNAS1 and STX16 |
| Pseudohypoparathyroidism Type 2 |
Normal |
↑
|
↓ |
↑
|
↓
|
increased urinary cAMP and phosphate |
GNAS1 (downstream) |
| Pseudopseudohypoparathyroidism |
Skeletal defects |
N
|
N |
N
|
N
|
|
GNAS1 (paternal defect) |
|
| Treatment |
- Calcium gluconate infusion
- with cardiac monitoring to prevent hypercalcemia)
- Activated vitamin D (calcitriol)
|