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SA Endocrinology > Hypoadrenocorticism > Flashcards

Hypoadrenocorticism Flashcards

1
Q

Actions of glucocorticoids

A

Part of the fight or flight response
A ‘stress’ hormone
Counteracts the effects of stress
Essential for life!

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2
Q

Aldosterone regulation

A

Renin-angiotensin system
- decreased blood pressure (baroreceptors in wall of afferent arteriole, and cardiac and arterial) -> renin release -> angiotensin release -> aldosterone release

Potassium concentration
- Very small increases -> aldosterone release

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3
Q

Function of aldosterone

A

Regulation of BP
Acts on cells of diatal tubule and collecting duct to increase reabsorption of Na, Cl and water
Stimulates secretion K+ into tubular lumen
Stimulates secretion of H+ in exchange for K+ in the collecting tubules, so regulating acid/base

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4
Q

Aetiology of hypoadrenocorticism

A
  1. Primary hypoadrenocorticism - Addison’s
  2. secondary hypoadrenocorticism - deficiency of ACTH
  3. Iatrogenic hypoadrenocorticism
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5
Q

Primary hypoadrenocorticism (Addisons)

A

Deficiency of glucocorticoids (cortisol) and mineralocorticoids (aldosterone).

Occurs with loss of 85-90%

Signalment: young/middle aged, female dogs. Very rare in cats.

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6
Q

Causes of Primary hypoadrenocorticism (Addisons)

A

Idiopathic atrophy - probably immune mediated destruction

Iatrogenic - drugs (mitotane, trilostane), surgery (bilateral adrenalectomy

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7
Q

Pathophysiology of Primary hypoadrenocorticism (Addisons)

A

Aldosterone deficiency
- loss of Na+, Cl, H2O
- retention of K+, H+
- Pre-renal failure

Glucocorticoid
- decreased stress tolerance
- GI signs
- Weakness
- appetite loss
- anaemia
- imparied gluconeogenesis

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8
Q

Seconday hypoadrenocorticism

A

Deficiency of ACTH
Only cortisol deficient as RAS system still stimulating aldosterone
Rare

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9
Q

Iatrogenic hypoadrenocorticism

A

Exogenous steroids -> adrenal atrophy

Cortisol deficiency only

Patient may have signs of Cushing’s syndrome: PU/PD, alopecia, pot belly, hepatomegaly

May develop signs of Addisons if steroids abruptly discontinued

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10
Q

Clinical signs of a chronic presentation of hypoadrenocorticism

A

Worsened by stress
Waxing and waning signs

Anorexia
Vomiting
Lethargy
Depression
Weakness
Shivering
Weight loss
PU/PD
Abdominal pain
GI haemorrhage

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11
Q

Acute presentation of Addisonian crisis

A

Medical emergency, can be fatal

Hypovolaemic shock, with paradoxical relative bradycardia

Collapsed or extremely weak
Hypothermic
History of V+/D+
Abdominal pain
Cardiac abnormalities
Depression
Thin
Weak
Dehydration
Bradycardia
Melena

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12
Q

Blood parameter changes in hypoadrenocorticism

A

Reflect lack of aldosterone and cortisol, and hypovolaemia

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13
Q

What does lack of aldosterone cause?

A

Renal loss of water, sodium, and chloride.
Retention of potassium and hydrogen ions.
Pre-renal failure

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14
Q

What does glucocorticoid deficiency cause?

A

Decreased stress tolerance, appetite loss, impaired gluconeogenesis, normocytic normochromic anaemia.

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15
Q

Biochemistry findings in hypoadrenocorticism

A

Hyperkalaemia
Hyponatraemia
Hypochloridaemia
Decreased Na:K ratio

10% do not have classic electrolyte findings

Azotaemia (increased renal parameters)
Hypercalcaemia
Hypoglycaemia

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16
Q

Haematology findings in hypoadrenocorticism

A

Lack of stress leukogram
Lymphocytosis
Eosinophilia
Neutropaenia
Anaemia

17
Q

Urinalysis findings in hypoadrenocorticism

A

May be high USG due to dehydration and azotaemia

BUT chronic sodium wasting can reduce urine concentrating - medullary washout

18
Q

ECG changes in hypoadrenocorticism

A

Result of the level of hyperkalaemia

> 5.5mmol/l: T wave peaking and Q-T shortening

> 6.5mmol/l: increased QRS duration

> 7.0 mmol/l: P wave decreased, P-R interval prolonged

> 8.5mmol/l: P waves absent and severe bradycardia

19
Q

Radiographic changes of hypoadrenocorticism

A

Usually relate to hypovolaemia e.g. microcardia, decreased pulmonary vessel size, reduced caudal vena cava, microhepatica.

Occasionally oesophageal dilation can be seen due to muscle weakness

20
Q

Features likely to make you suspicious of hypoadrenocorticism

A

Electrolyte abnormalities (Na+:K+ ratio <23) - but not always abnormal

Lack of stress leukogram in a sick dog

Young dog with a history of chronic illness

21
Q

Diagnostic tests for hypoadrenocorticism

A

Basal cortisol
ACTH stimulation
Aldosterone pre and post ACTH
Endogenous ACTH

22
Q

Basal cortisol in the diagnosis of hypoadrenocorticism

A

A value >55nmol effectively rules out hypoadrenocorticism.

If lower ACTH stimulation test is needed.

23
Q

ACTH stimulation test in the diagnosis of hypoadrenocorticism

A

The most useful test
Can also be used to diagnose atypical hypoadrenocorticism
A dog with hypoadrenocorticism will show no or minimal response to ACTH stimulation

24
Q

Aldosterone pre and post ACTH in the diagnosis of hypoadrenocorticism

A

Used to distinguish primary and secondary causes.

If secondary, dog will have raised post ACTH aldosterone, if primary it will have no response.

25
Q

Endogenous ACTH in the diagnosis of hypoadrenocorticism

A

Will be high in primary disease and low if secondary or iatrogenic disease

26
Q

Treatment of an acute Addisonian crisis

A
  1. Restore intravascular volume
  2. Reversal of hyperkalaemia
  3. Reversal of hyponatraemia
  4. Provision of glucocorticoids and mineralocorticoids
  5. (Correction of any life-threatening arrhythmias)
27
Q

Restoring intravascular volume in an Addisonian crisis

A

Using aggressive fluid therapy
0.9% NaCl or lactated Ringer’s (Hartmann’s) suitable
20-90 ml/kg/hr
Assess effectiveness frequently
Once volume restored reduce to maintenance rate
Continue fluids until hydratio status, urine output, serum electrolytes, and azotaemia are corrected.

28
Q

Reversal of hyperkalaemia in an Addisonian crisis

A

Can be life-threatening due to negative effects on myocardial cells

IV fluid therapy +++

10% Calcium gluconate

Sodium bicarbonate

IV dextrose/glucose

IV soluble insulin

29
Q

Reversal of hyponatraemia in an Addisonian crisis

A

Usually IV fluids are all thats needed

30
Q

Provision of glucocorticoids and mineralocorticoids in an Addisonian crisis

A

Acute period: IV administration of a rapid acting glucocorticoid
- Dexamethasone (can be used alongside ACTH stimulation test)
- Hydrocortisone
- Methylprednisolone sodium
- Prednisolone

Long term:
- Desoxycortone pivalate (mineralocorticoid replacement, no glucocorticoid activity so needs that too)
- Fludrocortisone (mineralocorticoid and glucocorticoid replacement, oral medication, now very expensive)

31
Q

Monitoring hypoadrenocorticism therapy

A

Do not repeat the ACTH stim test!
Clinical signs and electrolytes

32
Q

Prognosis of Addisonian crisis therapy

A

Good, providing the dog survives the acute event
Median survival time of 2.5 to 5.5 years following doagnosis

SA Endocrinology (11 decks)

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