Parathyroid adenoma

Question 1

When is parathyroid hormone released?

Answer 1

Parathyroid hormone is secreted in response to low ionised calcium levels by chief cells in 4x parathyroid glands situated posterior to thyroid glands.

Parathyroid glands are controlled by -ve feedback via calcium levels

Hyperparathyroidism => hypercalcaemia

Question 2

How does parathyroid gland act to increase calcium levels?

Answer 2

1. Increase osteoclast resorption of bone - releasing calcium & phosphate
2. Increasing intestinal absorption of calcium
3. Increasing synthesis of 1,25-dihydroxyvitamin D3
4. Increasing renal tubular reabsorption of calcium
5. Increasing excretion of phosphate

Question 3

What are the causes of primary hyperparathyroidism?

Answer 3

Solitary parathyroid adenoma (80%)

Diffuse hyperplasia of all glands (20%)

Parathyroid carcinoma (<0.5%)

Multiple parathyroid adenomas = rare and may be assoc. with MEN-1 (multiple endocrine neoplasia)

Question 4

What are the signs & symptoms of hyperparathyroidism?

Answer 4

Asymptomatic

Hypercalcaemia : Bones, Stones, Groans & psychic Moans

High calcium => weakness, tiredness, malaise, dehydration but polyuria, polydipsia, depression

Renal stones

Abdominal pain ; duodenal ulcers

Pancreatitis

Bone pain, fractures, osteopenia/osteoporosis - due to bone resorption

Hypertension (check calcium in people with high BP)

Question 5

How do you investigate for hyperparathyroidism?

Answer 5

Biochemistry:

Serum PTH, calcium, phosphate
=> Hypercalcaemia and hypophosphataemia with elevated PTH is the hallmark of primary hyperparathyroidism

Renal function test (U&E)

24h urinary calcium

High ALP - due to severe bone resorption

Imaging:

Osteitis fibrosa cystica (due to severe resorption)
=> may show up as subperiosteal erosion, cysts, brown tumours of phalanges ± pepper pot skull

DEXA for osteoporosis

Question 6

How do you treat mild hyperparathyroidism?

Answer 6

Increase fluid intake to prevent stones

Avoid thiazide

High calcium & vitamin D intake

6 monthly follow up

Question 7

When is surgical removal indicated in hyperparathyroidism?

What are its complications?

Answer 7

Excision of adenoma or all four hyperplastic glands
=> prevents stones, avoid peptic ulcers

Indications:
=> high serum or urinary calcium
=> bone disease
=> osteoporosis
=> reduced renal function
=> age <50yrs

Complications:
Hypoparathyroidism

Recurrent laryngeal nerve damage - hoarseness

Symptomatic calcium drop (hungry, bone syndrome, check calcium daily for >14d post-op)

Question 8

What causes secondary hyperparathyroidism?

How do you treat it?

Answer 8

Low calcium, high PTH => physiological compensatory hypertrophy of all parathyroid glands because of hypocalcaemia

Causes of hypocalcaemia : low vitamin D intake, chronic renal disease

Treatment:
=> Correcting underlying cause
=> Phosphate binders
=> Vit D

Question 9

What causes tertiary hyperparathyroidism?

How do you treat it?

Answer 9

After long-standing secondary hyperparathyroidism => glands become hyperplastic => most often seen in renal failure

=> Plasma calcium & phosphate both raised
=> PTH raised

Question 10

Malignant hyperparathyroidism:

Parathyroid hormone protein is produced in squamous cell lung cancer, breast and renal cell carcinomas

=> mimics PTH resulting in hypercalcaemia

Answer 10

INFO CARD