Parathyroid

Question 1

Parathyroid:

Normal PTH secretion and calcium homeostasis?

Answer 1

low Ca stimulates PTH secretion from the parathyroid gland

Results in:

• increased vitamin D synthesis
• calcium resorption from bone, absorption from gut, reabsorption from kidney
• phosphate resorption from bone kidney
• increased magnesium reabsorption
• reduction in bicarbonate reabsorption

Calcium measurement
Total Ca = free and bound combined

bound = to albumin and phosphate

Acidosis = increased free Ca = reduced PTH
Alkalosis = reduced free Ca = elevated PTH

Question 2

Parathyroid:

Types of parathyroid derrangement?

Answer 2

Primary (parathyroid tumour) = increased/normal PTH, increased Ca

Secondary (Chronic Renal Failure or vitamin D deficiency) = increased PTH often due to hypertrophy), low/normal Ca

Tertiary (treated but residual hyperplasia) = very elevated PTH, very elevated Ca

Malignancy = low PTH (appropriately suppressed), increased Ca

Question 3

Parathyroid:

Renal osteodystrophy mechanism?

Answer 3

1) As renal function declines vitamin D synthesis declines and calcium reabsorption is limited
2) Cycle of Ca levels drops/phosphate elevation which the PTH levels rise in response to
3) Eventually Ca levels drop too much to be compensated for despite continued elevations of PTH

https://www.fortunejournals.com/fulltext-images/chronic-kidney-diseasemineral-and-bone-disorders-ckdmbd-03.png

Question 4

Parathyroid:

Primary Hyperparathyroidism?

Answer 4

post menopausal women

risk factors:

• lithium therapy
• head or neck irradiation

Symptoms:
Hypercalcaemia (Stones, bones, groans and psychic moans)

85% cause by solitary parathyroid adenoma

95% cure rate with surgical removal

**Must exclude Familial Hypercalciuric Hypercalcaemiua (FHH)

Question 5

Parathyroid:

Familial Hypercalciuric Hypercalcaemia (FHH)?

Answer 5

benign condition
autosomal dominant
hypercalcaemia from birth
result of inactivated calcium sensing receptors

how to rule it out?
Fraction of urinary calcium = (Urine Ca x Serum Ca)/(Serum Ca x Urine Creatinine)
If > 0.02 = primary hyperparathyroidism
if < 0.01 = FHH

Question 6

Parathyroid:

Hypercalcaemia?

Answer 6

Causes:

• malignancy (inappropriate release of PTH-related peptide from tumour cells, associated with lung, breast, prostate, colon and T-cell malignancies and MM)
• post-hypocalaemic hypercalcaemia (recovery from pancreatitis, ARF, rhabdomyolysis)
• primary hyperparathyroidism
• adrenal insufficiency
• prolonged immobilisation
• granulomatous disease – sarcoidosis, TB, beryliosis, leprosy, histoplasmosis (increase in 1,25(OH)2D production from macrophages in granuloma)
• vit A and D intoxification
• thyrotoxicosis
• acromegaly
• phaeochromocytoma
• chronic lithium therapy
• secondary hyperparathyroidism
• tertiary hyperparathyroidism

Symptoms:
Stones, bones, groans and psychic moans

• RENAL – polyuria, stones, dehydration
• bone aches
• GIT = constipation, anorexia, nausea, vomiting, pancreatitis
• NEURO – lethargy, hypotonia, confused, coma
• CVS – arrhythmias (shortened QTc and Osborne waves)

Question 7

Parathyroid:

Hypocalcaemia?

Answer 7

Causes:

• reduced intake
• increased losses - diuretics
• redistribution (hyperphosphataemia, alkalosis, pancreatitis, rhabdomyelitis, tumour lysis, hypoparathyroidism)

Symptoms:

• perioral numbness
• paraesthesia
• cramps
• seizures

Signs:

• tetany
• Trousseau (BP cuff inflation traps excitable median nerve resulting in carpal spasm
• Chvostek (tap facial nerve results in facial muscle spasm)
• hypotension
• long QT