Hormones for Calcium Balance
- Three key hormones: PTH, Vitamin D, Calcitonin.
Stimulus for PTH secretion:
- Hypocalcemia
- Mild hypomagnesemia.
- Severe hypomagnesemia inhibits PTH secretion.
- Hyperphosphatemia
- Lithium
Parathyroid Gland
- Superior parathyroid gland:
- From 4th pharyngeal pouch
- Superior “PARA” → 4 letter
- Inferior parathyroid gland:
- From 3rd pharyngeal pouch
- Migrates with thymus
- Inferior “PARA” → 4 - 1 = 3 letter
- Supplied by Inferior Thyroid Artery
- Risk of devascularisation if capsular branches ITA ligated far from gland
Parathyroid Supply:
- ITA Branch of thyrocervical trunk
- Capsular branches (ITA):
- Ligated close to gland
- Avoids parathyroid devascularisation
- Superior Thyroid Artery:
- Ligated close to gland during surgery
- Saves ELN
Hyperparathyroidism
Clinical Features Hyperparathyroidism
- M/c/c → Parathyroid Adenoma
(Mnemo: Stones, Bones, Abdominal Groans, Psychiatric Overtunes)
- Bones:
- Pathological #.
- Brown tumours (Von Recklinghausen disease of bone).
- Osteitis fibrosa cystica/brown tumors.
- Sub periosteal resorption.
- Salt and pepper skull.
- Stones:
- Multiple + recurrent renal stones (m/c feature).
- Abdominal Groans:
- Colicky abdominal pain, pancreatitis.
- Psychiatric Overtunes.
1° Hyperparathyroidism
- Adenoma > Hyperplasia.
Investigations
Examination
- Band keratopathy
- Deposition of calcium in corneal stroma
Biochemical:
- PTH ↑.
- Ca²⁺ ↑.
- PO₄⁻ ↓.
- Urinary Ca²⁺ ↑.
- Urinary PO₄⁻ ↑.
SPECT (Single-photon emission CT) Sestamibi (3D) >> Tc 99 MiBi Scan (2D)
- 3D scintigraphy
- Type of CT imaging.
- Provides better resolution than planar scintigraphy.
- Best type: SPECT Sestamibi
- P → Photon
- Localises parathyroid gland.
- Sestamibi SPECT has better resolution than Sestamibi alone
- HMPAO SPECT → Used for cerebral perfusion.
- Mnemonic: Hambaoo → dance → blood perfuse into brain
B/L Nephrocalcinosis/ Medullary Nephrocalcinosis
- Lucent areas are observed between opaque areas.
- 2 causes
- A/w Hyperparathyroidism
- Medullary sponge kidney
- Functional kidney
- Causes subperiosteal bone resorption.
- Hand X-ray (middle phalanx) shows the earliest bone changes.
- Radiological Features:
- Concavity of bone due to subperiosteal resorption.
- Salt and pepper appearance in the skull or pepper pot skull.
- Due to lytic lesions.
- Brown tumor or osteitis fibrosa cystica or Von Recklinghausen disease of bone
ECG
- Short QT
- Prolonged PR
Mx
- Adenoma:
- Only 1 gland out of 4 is enlarged
- Remove affected gland
- Hyperplasia:
- 3 ½ gland removed.
- 1 ½ gland autotransplanted in brachioradialis (m/c) of forearm of non-dominant hand.
- (If recurrence: Easy removal).
Miami Criteria (Intra-op PTH assay)
- To ensure correct gland is removed
- Pre-op PTH level → 10-15 mins after Sx → PTH level ↓ by >50% → Correct gland removed.
- Half by 10 mins
Recurrence assessment
- Casanova test
- Selective venous catheterisation for PTH
- Positive → recurrence in the neck or graft (graft hyperplasia).
2° Hyperparathyroidism
- ↑ PTH (High but appropriate)
- Parathyroid hyperplasia, reversible condition
Causes
- Chronic Renal Failure (CRF)
- Defective intestinal absorption
- Lithium intake
- Vitamin D₃ deficiency
Mx
- Correction of CRF.
- Non calcium containing Phosphate binders
- Initial treatment of choice
- Sevelamer
- Vit D₃ Supplement.
- Low phosphate diet.
- Calcitriol and Cinacalcet
- ↓ Level of PTH in secondary hyperparathyroidism
- Also cause ↑ serum phosphate levels
- Bisphosphonates are not used
Phosphate binders
- Calcium containing
- Avoided in Chronic Renal Failure
- due to ↑↑ Calcium
- Calcium acetate
- Calcium carbonate
- Non calcium containing
- Sevelamer
- Lanthanum
Pseudohyperparathyroidism
(AKA Hypercalcemia of malignancy)
- M/C paraneoplastic syndrome → PTH related peptide mediated.
- A/w:
- SCC lung.
- Metastatic ca:
- Prostate ca.
- Breast ca.
- C/F: Altered Sensorium & dehydration.
- Mx:
- IV fluids (1st line) f/b Diuretics (Lasix).
- DOC: Bisphosphonates (When RFT N and urine output adequate).
Physiology of Vitamin D:
- Vit D3 — (25 hydroxylase) —> 25-OH-Vit D3 — (1 alpha hydroxylase) —> 1, 25, (OH)2 VitD3 (Active form of Vit D).
- PTH increases Ca & P absorption.
- 1, 25, (OH)2 VitD3 has feedback inhibition of PTH
Categories of Rickets based on investigations include:
Vitamin D Dependent Rickets
- A/w endodermal dysplasia
- VDDR Type 1
- Vitamin D not converted to active form
- VDDR Type 2
- Active form cannot act on receptors
Vitamin D Resistant Rickets
- ↑↑ FGF 23 levels → ↑ renal phosphate wasting → ↓ Vitamin D
- Congenital Hypophosphatemic Rickets
- X Linked Dominant
- PHEX gene
- Mnemonic: Phex Phosphate FGF
- Acquired Hypophosphatemic Rickets
- Some benign mesenchymal tumors
- Secrete FGF-23
- Phosphaturia & hypophosphatemia.
NOTE
Pseudohypoparathyroid/ Albright Hereditary Osteodystrophy (AHO)
in Pseudohypoparathyroid and PseudopseudohypoPTH
- Maternal
- Type 1 A → AD
- GNAS Mediated
- Mimic secondary Hyper PTH
- Mother → Lie to child (pseudo)
- PTH is high but cannot act
- (Same Pic as CKD, but Normal ALP)
- Psudo pseudo
- knuckle knuckle dimple dimple
- NOTE: If only short 4th Metacarpal
- Turner
PseudopseudohypoPTH
- Paternal
- AD
- Everything is normal
- Father → Lie to child and mother (pseudo pseudo) → but everything will be normal
Madelung
- Distal radial abn
- Seen in Turner’s syndrome
- Radius is not formed
- Radio carpal coalation doesnt take place
ㅤ | Williams syndrome | Marfan syndrome |
Mutations | Elastin Mutation | Fibrillin Mutation |
Leads to | Supravalvular aortic stenosis | Dilatation of aortic root ↳ Rupture → Death |
ㅤ | ㅤ |
Supravalvular AS | • Vitamin D toxicity • William syndrome |
Supravalvular PS | • Noonan syndrome |
ㅤ | Seen in |
GNAS | • Mccune Albright • Cardiac Myxoma |
GNAS 1 | • Pseudohypoparathyroid/ Albright Hereditary Osteodystrophy |
GNAQ | • Sturge Weber (Sporadic) |
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