ChemPath 20: Clin Chem CPC

Question 1

Describe the effect of hypokalaemia on the myocardium.

Answer 1

Increases myocardial irritability

Question 2

Describe the cardiac consequences of plasma potassium being too high or too low.

Answer 2

Hypokalaemia – ventricular fibrillation

Hyperkalaemia – asystole (ultimate stable rhythm)

Question 3

What is the difference between a Colles’ fracture and a Smith’s fracture?

Answer 3

Colles’ – fracture caused by falling on an outstretched hand. The radial head will be displaced backwards (away from the palm)

Smith’s – fracture caused by falling on a flexed wrist. The radial head will be displaced forwards (towards the palm)

Question 4

What is a Pott’s fracture?

Answer 4

Ankle fracture involving the tibia and fibula

Question 5

What would you expect to see on the urine dipstick of someone with subacute bacterial endocarditis?

Answer 5

Microscopic haematuria

Question 6

What is the differential diagnosis for hypercalcaemia?

Answer 6

Cancer

Primary hyperparathyroidism

Sarcoidosis

Question 7

What is the physiological role of PTHrP (Parathyroid hormone-related protein)?

Answer 7

Our genome encodes a gene for PTHrP

This is important in foetal life because it allows us to steal calcium from our mother to help form our skeleton

NOTE: PTHrP is also produced by the lactating breast
NOTE: PTHrP stimulates cancer cells to invade bone

Question 8

What are the two main mechanisms of hypercalcaemia of malignancy?

Answer 8

PTHrP

Cancer invading bone

Question 9

Main actions of PTH?

Answer 9

Increase calcium liberation from bone (osteoclast activity)

Increase calcium reabsorption in the kidneys

Increase calcium absorption in the intestines

Activates 1-alpha hydroxylase in the kidneys (thereby increasing activation of vitamin D)

Increase phosphate excretion

Question 10

Name and describe an eye sign of hypercalcaemia

Answer 10

Band keratopathy – calcium deposition across the front of the eye

It is a feature of chronic hypercalcaemia (i.e. it will not be caused by hypercalcaemia of malignancy)

Question 11

What is a key difference between calcium stones and urate stones?

Answer 11

Calcium stones are radio-opaque

Urate stones are radiolucent

Question 12

List some complications of hypercalcaemia.

Answer 12

Renal stones

Pancreatitis

Peptic ulcer disease

Skeletal changes (osteitis fibrosa cystica)

Question 13

List some risk factors for hypercalcaemia.

Answer 13

Family history

Dehydration

Hyperparathyroidism

Question 14

Which bacterium has a predilection to infect urinary tract stones?

Answer 14

Proteus mirabilis

Question 15

What are the main investigations used for urinary tract stones?

Answer 15

CT-KUB w/out contrast

Stone analysis

Urine and serum biochemistry

Question 16

What are some management options for urinary tract stones?

Answer 16

Lithotripsy

Lithotomy

Cystoscopy

Question 17

Urinary tract stone prevent?

Answer 17

Drink more water 
Treat hypercalciuria (thiazides)

NOTE: loop diuretics increase urine calcium

Question 18

At what point would you use emergency management of hypercalcaemia?

Answer 18

When serum calcium > 3 mmol/L or very unwell (e.g. dehydrated, confused, drowsy, seizures)

Question 19

Outline the emergency management of hypercalcaemia.

Answer 19

IV access
Insert catheter

3-6 L 0.9% saline over 24 hours

The first litre should be given quickly (over 1 hour) to correct dehydration

Elderly patients should also be given furosemide (to prevent pulmonary oedema)

Question 20

Which other drug may be used under desperate circumstances when managing hypercalcaemia?

Answer 20

Pamidronate (IV) - bisphosphonate

Good at treating bone pain but takes at least 1 week to start working and gets incorporated into bone for a very long time

Question 21

In which group of patients would you use dextrose rather than saline (in hypercalcaemia mx)?

Answer 21

Liver failure – they have a tendency to retain salt

Question 22

Outline the treatment of non-emergency hypercalcaemia.

Answer 22

Keep well hydrated

Avoid thiazides (they reduce hypercalciuria but they increase plasma calcium concentration)

Surgery

Question 23

What is minimally invasive parathyroidectomy?

Answer 23

A technetium sesta MIBI scan shows a hyperactive parathyroid

An USS is also performed and if the results of the sesta MIBI and USS are concordant, the whole neck does not need to be opened

If they are not concordant, the surgeon will need to view all four glands and take out the largest one

Question 24

What feature may you see on an X-ray of the hands in a patient with primary hyperparathyroidism?

Answer 24

Cystic changes in the radial aspect

Question 25

What is a characteristic histological feature of long-standing undiagnosed hyperparathyroidism?

Answer 25

Brown tumours – they are multinucleated giant cells in the bone. The giant cells are activated osteoclasts

Question 26

What is the mainstay of treatment of sarcoidosis?

Answer 26

Steroids

Question 27

What is the histological hallmark of sarcoidosis?

Answer 27

Non-caseating granulomas

Question 28

Outline the mechanism of hypercalcaemia in sarcoidosis.

Answer 28

Macrophages in the lungs express 1-alpha hydroxylase This activates vitamin D NOTE: patients are more likely to become hypercalcaemic in the summer months because of increased exposure to sunlight

Question 29

A 35 year old woman presents with right loin-to-groin pain. She describes this as 10/10 in severity. A urine dipstick is performed which shows the following: Leukocytes +ve Nitrites –ve Glucose –ve Blood +ve What is the most likely cause? Cystitis Pyelonephritis Renal stones Bladder cancer Diabetes mellitus

Answer 29

Renal stones - Loin to groin + absence of nitrites suggests this

Question 30

Most appropriate ix for renal stones?

Answer 30

CT KUB (w/out contrast) AXR- may be useful some stones are radiolucent CT KUB w/ contrast - less sensitive

Question 31

Most common composition of renal stones? What about composition of those most likely to cause stag horn calculi (bilateral esp)?

Answer 31

Most common - Calcium oxalate Staghorn - Struvite (magnesium ammonium phosphate)

Question 32

What organism are struvite renal stones associated w/?

Answer 32

Proteus mirabilis

Question 33

A 55 year old man presents to A&E with loin-to-groin pain. A CT KUB identifies a right 7mm obstructing stone in the renal pelvis. His blood results are below: Raised Ca, Urea, Creatinine Low Phosphate Normal ALP and PTH What is the most likely underlying cause?

Answer 33

PTH is inappropriately normal - even though high Ca Deranged U+Es due to post-renal AKI Hence this is caused by Primary hyperparathyroidism

Question 34

What are some conditions that cause HIGH Ca? What is the Ca, phosphate, PTH and ALP like in these conditions?

Answer 34

Primary hyperPTH - Raised Ca - Low Phosphate - Raised / Normal PTH - Normal ALP Tertiary hyperPTH - Raised Ca - Raised Phosphate - Raised PTH - Normal ALP Malignancy - Raised Ca - Normal Phosphate - Low PTH - Normal ALP

Question 35

What are some conditions that cause NORMAL Ca? What is the Ca, phosphate, PTH and ALP like in these conditions?

Answer 35

Osteoporosis - Normal Ca - Normal Phosphate - Normal PTH - Normal ALP (can be raised if fracture) Pagets Disease - Normal Ca - Normal Phosphate - Normal PTH - Raised ALP Pseudo-pseudohypoPTH - Normal Ca - Normal Phosphate - Normal PTH - Normal ALP

Question 36

What are some conditions that cause LOW Ca? What is the Ca, phosphate, PTH and ALP like in these conditions?

Answer 36

Secondary hyperPTH - Low Ca - Low (if vit D deficient) / Raised (if CKD) Phosphate - Raised PTH - Raised ALP PseudohypoPTH - Low Ca - Raised Phosphate - Raised PTH - Normal ALP

Question 37

A 55 year old man presents to A&E with loin-to-groin pain. His calcium is 3.05 and he has a renal stone. What is the most appropriate 1st line management option?

Answer 37

IV Fluids - 0.9% NaCl, 4+ litres daily

Question 38

A 45 year old Afro-Caribbean woman presents to A&E with loin-to-groin pain. She also has tender, erythematous nodules on both her shins, which she’s had for 1 week. Her blood results are shown below: Raised Ca Low PTH Which enzyme is activated by her underlying condition to cause hypercalcaemia?

Answer 38

1a-hydroxylase Sarcoidosis w/ erythema nodosum Macrophages in sarcoidosis' non-caseating granulomas produce 1a-hydroxylase which activates vit D