Chempath 20: Clinical Chemistry CPC

Question 1

Which fracture is most likely if you slip and fall on outstretched hands ?

Answer 1

Cole’s fracture

Radius fractures backwards away from the palm side

Question 2

What fracture is caused by falling on a flexed wrist ?

Answer 2

Smith’s fracture

Question 3

List 3 causes of hypercalcaemia ?

Answer 3

Primary hyperparathyroidism
Cancer
Sarcoidosis

Question 4

How can you differentiate Primary hyperparathyroidism from cancer causing hypercalcaemia ?

Answer 4

Plasma PTH

0 in cancer and high in primary hyperparathyroidism

Question 5

What is PTHrP ?

Give 2 locations where its produced ?

Answer 5

PTH related peptide

Produced by the placenta (so mothers calcium increases and baby can steal some)
produced by breast and secreted into breast milk

Question 6

Why is PTHrP activation in cancer a bad prognostic feature ?

Answer 6

PTHrP stimulates cancer invasion of bone by turning on osteoclasts.

Question 7

Which enzyme activates Vitamin D in the kidneys ?

Answer 7

1-alpha hydroxylase

Question 8

How does vitamin D affect the kidneys ?

Answer 8

Activated vitamin D (calcitriol) causes increased reabsorption of calcium

Question 9

Which tumours are featured in MEN1 ?

Answer 9

Pituitary tumour
Parathyroid tumour
Pancreas - islet cell tumour

Question 10

What symptoms do you get with hypercalcaemia ?

Answer 10

Moans- depression, psychosis, coma
Groans- constipation, abdominal pain,
Bones- fractures, bone pain (osteitis fibrosa cystica)
Stones- renal colic (calcium oxalate stones)

Polydipsia and polyuria (nephrogenic diabetes insipidus)

Question 11

Which organism causes recurrent UTIs in patients with calcium stones ?

Answer 11

Proteus mirabilis

Question 12

Why are patients so dehydrated with Hypercalcaemia ?

Answer 12

Calcium acts like mannitol, it causes water to move with it into the urine causing a diuresis

Question 13

How do you treat hypercalcaemia ?

Answer 13

• Saline fluids (to rehydrate)
• Furusamide (causes calcium loss in the urine)
• IV pamidronate (a bisphosphonate that stops bone resorption by causing osteoclast apoptosis. Only use in very high calcium)

Question 14

Why is giving saline to hypercalcaemia patients with liver failure contraindicated ?

What do you give instead ?

Answer 14

They retain salt so can cause hypernatraemia

Dextrose Fluids

Question 15

Which diuretics should be avoided in hypercalcaemia ?

Answer 15

Thiazides

They cause increased calcium reabsorption into the blood.

Question 16

Which feature of Osteitis fibrosa cystica is described by this histology:

“Multinucleate giant cells in the bone”

Answer 16

Brown tumours

Giant cells are the activated osteoclasts

Question 17

A lady is noted to have hypercalcaemia, her chest X ray shows bilateral hilar lymphadenopathy.

What is the most likely diagnosis ?

Answer 17

Sarcoidosis

Question 18

A histology specimen of a patient with hypercalcaemia shows “non-caseating granuloma”.

What is the most likely diagnosis ?

Answer 18

Sarcoidosis

Question 19

What is the mainstay of treatment for sarcoidosis ?

Answer 19

Steroids

Question 20

How does sarcoidosis cause Hypercalcaemia ?

Answer 20

• Macrophages in the lungs of people with sarcoidosis express 1-alpha-hydroxylase.
• This causes increased activation of vitamin D (especially in the summer)
• Activated Vitamin D causes increased calcium reabsorption from the kidneys and G.I tract