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SA Endocrinology > Calcium and phosphorus homeostasis > Flashcards

Calcium and phosphorus homeostasis Flashcards

1
Q

Important factors in calcium homeostasis

A

Parathyroid hormone
Vitamin D
Calcitonin
PTHrP
Renal function

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2
Q

What do PTH and vitamin D alter to regulate calcium levels?

A

Renal reabsorption and loss
Uptake and loss of calcium from bone
Gut uptake and loss of calcium from bone

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3
Q

Action of calcitonin

A

Acts on bone to prevent calcium mobilisation through osteoclastic activity

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4
Q

PTHrP

A

PTH-like factor
Important role in mediating hypercalcaemia of malignancy
Involved in calcium regulation in the foetus and is also secreted into milk so role in neonate
In malignancy PTHrP can mimic the action of PTH

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5
Q

Phosphate

A

Most abundant intracellular anion.
80-85% stored as hydroxyapatite in bone, 15% in soft tissues such as muscle.
Vitamin D promotes calcium and phosphate uptake in the gut.

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6
Q

Hyperphosphataemia

A

Occurs most commonly with renal insufficiency

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7
Q

Causes of hypophosphataemia

A

Shift into intracellular space
- insulin therapy
- IV glucose administration
- Respiratory alkalosis
- Metabolic acidosis

Increased urinary excretion
E.g. DM, hyperparathyroidism etc.

Decreased gut absorption
E.g. decreased intake, malabsorption

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8
Q

Differential diagnoses of hypercalcaemia in dogs

A

Most commonly malignancy
- Lymphoma
- Anal sac adenocarcinoma
- Multiple myeloma
- Etc.

Primary hyperparathyroidism

Hypoadrenocorticism (Addisons)

Chronic renal failure

Vitamin D intoxication

Granulomatous disease

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9
Q

Parameters of primary hyperparathyroidism

A

Increased total calcium, ionised calcium, and PTH

Decreased phosphate

Normal PTHrP

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10
Q

Parameters of secondary renal hyperparathyroidism

A

Total calcium increased, normal, or decreased

Ionised calcium decreased or normal

Increased phosphate

PTH increased or high normal

PTHrP normal or increased

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11
Q

Hypervotaminosis D

A

Iatrogenic (cod liver oil)
Plants (calcitriol glycosides)
Rodenticides (cholecalciferol)
Anti-psoriasis creams (calcipotriol or calcipotriene)

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12
Q

Idiopathic hypercalcaemia in catz

A

Most common cause of ionised hypercalcaemia in cats

Clinical signs mild or none

PTH, PTHrP and calcitriol suppressed in most

Renal function is normal, at least initially

Calcium oxalate uro lithuania is common

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13
Q

Causes of IHC in cats

A

Unknown
Inappropriate dietary vit D may play a role
Mutations in vit D receptors
Other genetic causes

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14
Q

Management of idiopathic hypercalcaemia in cats

A

Diurese using normal saline

Diet
- high fibre
- renal
- diets for calcium oxalate urolithiasis

Steroids (preds)
- decreases absorption and resorption, and skeletal mobilisation

Bisphosphonates
- reduce activity and no of osteoclasts

Calcimimetics
- lower iCa, phosphorus, and PTH concentrations

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15
Q

Primary hyperparathyroidism in dogs

A

Usually occurs in middle-older aged dogs (8-12yrs, mean 11.2yrs)

Onset of disease can be slow and insidious and is often ignored as part of the normal aging process

Many dogs diagnosed when being investigated for other conditions or when undergoing health checks

Clinical signs may be mild or not perceived to be present at all

Keeshonden have the highest breed predisposition

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16
Q

Clinical signs of Primary hyperparathyroidism in dogs

A

Mild to moderate hypercalcaemia may cause no obvious clinical signs

Can cause PU/PD

Muscle weakness and exercise intolerance

Inappetence and weight loss

Constipation

Facial pruritus and oral discomfort

Calcium-containing urolithiasis

Renal failure

17
Q

Diagnosis of Primary hyperparathyroidism in dogs

A

Demonstration of hypercalcaemia alongside hyperparathyroidism

Both total and ionised calcium will be elevated

Phosphate low or low normal

PTHrP will be normal

Survey radiographs for neoplasia often unremarkable

Cervical ultrasound examination often shows a single enlarged parathyroid gland
○ Ideally a single parathyroid nodule would be identified with other glands not visible
○ Occasionally, more than one gland is enlarged

Scintigraphy can be used to identify affected parathyroid gland but this is often unrewarding

Selective venous sampling for serum PTH is equally unreliable

18
Q

Incidence of renal damage and failure in Primary hyperparathyroidism in dogs

A

Many Keeshonds and other breeds who develop PHPT do not experience renal damage

However, those who do can be very severely affected

Renal insufficiency can be recognized both before and after treatment

19
Q

Treatment options for Primary hyperparathyroidism in dogs

A

Surgery:
- Parathyroid nodules are usually dark red in colour and can be palpated if not seen easily, attached to thyroid issue

Percutaneous ethanol injection

Heat ablation

All have high success rates

20
Q

Problems associated with treatment of Primary hyperparathyroidism in dogs

A

Post-treatment monitoring is essential in dogs with PHPT

Ideally patients would stay in hospital for at least 5 days

The higher the pre-treatment calcium, the more likely there are to be side-effects

Severely hypercalcaemic dogs need to be pre-treated with vitamin D and calcium supplements 12-24 hours before treatment to avoid dramatic changes in calcium as PTH drops.

Clinical signs can be seen in dogs whose calcium is still relatively high, but that is substantially lower than previously

21
Q

Emergency treatment for hypercalcaemia

A

Saline diuresis

Frusemide

Bisphosphonates (clodronate, alendronate, pamidronate)

Calcitonin

This route is rarely necessary for dogs with PHPT as the primary cause of the hypercalcaemia is generally addressed relatively quickly

22
Q

Treatment of post-operative hypocalcaemia

A

Intravenous 10% calcium gluconate is given as a short term and emergency treatment

Needs to be given slowly over 10-30 minutes to effect – monitor ECG for bradycardia, VPCs etc.

CRI can be used until oral therapy is effective

Vitamin D analogues such as 1,25,dihydroxycholecalciferol (calcitriol) or One-Alfa (alfacalcidol) can be used

Calcium carbonate has the highest percentage of calcium and lowest cost

For long term support, commercial pet food should have enough dietary calcium to avoid the need for supplementation

23
Q

Common causes of hypocalcaemia

A

Hypoalbuminaemia

Acute or chronic renal failure

Acute pacreatitis

Eclampsia

Hyperthyroidism

Urinary tract obstruction

Individual variation

24
Q

Less common causes of hypocalcaemia

A

Hypoparathyroidism

Toxic causes - ethylene glycol

Iatrogenic causes

Critical illness of various aetiologies

25
Q

PTH related causes of hypocalcaemia

A

PTH low
Calcium low
Phosphate high

26
Q

Vitamin D related causes of hypocalcaemia

A

PTH high
Calcium low
Phosphate low

27
Q

Causes of significant hypocalcaemia

A

Primary hypoparathyroidism (PTH low, calcium low, phosphate high)

GI malabsorptive disease (PTH high, calcium low, phosphate low)

Eclampsia (calcium low, PTH and vit D attempting to compensate but variable according to mechanism of development)

28
Q

PTH low, calcium low

A

Hypoparathyroidism

29
Q

Low calcium, high PTH

A

Ethylene glycol toxicity
Sepsis
Critical care patient
Phosphate enema
Eclampsia

30
Q

PTH slightly high and calcium slightly low

A

Hypovitaminosis D

31
Q

PTH high and calcium slightly low

A

Renal secondary hyperparathyroidism

32
Q

High calcium, high PTH

A

Hyperparathyroidism

33
Q

High calcium, low PTH

A

Idiopathic hypercalcaemia

34
Q

Clinical signs associated with hypocalcaemia

A

NM excitability
- muscle fasciculations
- face rubbing
- biting/licking paws or body
- hypersensitivity to external stimuli
- stilted gait
- ataxia

Behavioural changes
- agitation
- anxiety
- vocalisation
- aggression

Other
- panting
- hyperthermia
- cataracts

35
Q

When do dogs become hypocalcaemic?

A

Primary hypoparathyroidism

Secondary to surgery to treat primary hyperparathyroidism

When they have intestinal malabsorption syndromes such as lymphangiectasia

Sepsis

Post-partum hypocalcaemia (puerperal tetany, eclampsia)

Most common in small breeds, least common in giant breeds

36
Q

Treatment for hypocalcaemia

A

Calcium
- IV or oral
- Can cause thrombophlebitis and skin necrosis and sloughing if SQ

Vitamin D preparations
- Differ in the time to onset of effect and what, if any modifications they require

37
Q

Magnesium

A

Like calcium and is active in the ionised form

The second most abundant intracellular cation after calcium

A cofactor of the Na/K ATPase pump that keeps Na and K in their extra and intracellular compartments respectively

Essential for release of PTH; a deficiency can lead to functional hypoparathyroidism

SA Endocrinology (11 decks)

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