Physiology of hypoadrenocorticism

Question 1

How is decreased BP detected?

Answer 1

Baroreceptors in arteriole walls
Cells of macula densa in early distal tubule are stimulated by a reduction in NaCl delivery
=> renin release

Question 2

Describe the classification of hypoadrenocorticism

Answer 2

Primary hypoadrenocorticism:
- Addison’s disease
- loss of adrenal cortex
Secondary hypoadrenocorticism:
- deficiency of ACTH
Iatrogenic hypoadrenocorticism:
- exogenous steroids
- e.g., suddenly stopping steroid therapy

Question 3

Describe Addison’s disease/primary hypoadrenocorticism

Answer 3

Deficiency of glucocorticoids (cortisol) and mineralocorticoids (aldosterone)
Occurs with loss of 85-90% of adrenal cortex

Question 4

Describe the causes of Addison’s disease/primary hypoadrenocorticism in dogs

Answer 4

Idiopathic atrophy - immune-mediated destruction
Iatrogenic:
- drugs e.g., mitotane
- surgery e.g., bilateral adrenalectomy

Question 5

Describe secondary hypoadrenocorticism

Answer 5

Deficiency of ACTH
Disease of pit gland
Only effect glucocorticoids, not mineralocorticoids

Question 6

Describe iatrogenic hypoadrenocorticism

Answer 6

Exogenous steroids => adrenal atrophy
Cortisol deficiency only
May have signs of Cushing’s syndrome
May develop signs of Addison’s disease if steroids abruptly stopped

Question 7

Describe the signalment of Addison’s disease

Answer 7

Young-middle aged dogs
mostly females
Rare in cats
Breed disposition in:
- poodles
- bearded collies
- Great dane
- rottweiler

Question 8

Describe the pathophysiology of hypoadrenocorticism

Answer 8

Aldosterone deficiency:
- loss of Na+, Cl- and H20
- retention of K+ and H+
- pre-renal renal failure
Glucocorticoid deficiency:
- decreased stress tolerance
- GI signs
- weakness
- inappetance
- anaemia (effect of cortisol of erythropoiesis)
- impaired gluconeogenesis

Question 9

Describe the history and clinical signs of chronic hypoadrenocorticism

Answer 9

Vague and non-specific signs worsened by stress - appear normal between bouts
Anorexia
Vomiting
Diarrhoea
PU/PD (Na and water loss)
Weakness
Lethargy
Depression

Question 10

Describe the history and clinical signs of acute hypoadrenocorticism

Answer 10

Recent history of vomiting and diarrhoea
Signs caused by hypovolaemic shock:
- collapsed or very weak
- bradycardia (due to hyperkalaemia)
- abdominal pain

Question 11

Describe the clinical pathology of the complete blood count in hypoadrenocorticism

Answer 11

Anaemia:
- decreased erythrocytosis due to lack of cortisol
- GI blood loss

Question 12

Describe the clinical pathology of hypoadrenocorticism: biochemistry

Answer 12

Electrolyte imbalance:
- hyperkalaemia (increased K+)
- hyponatraemia (Decreased Na+)
- hypochloridaemia (decreased Cl-)
- Na:K ration <23
Due to aldosterone deficiency:
- decreased renal tubular resorption of Na+ and Cl-
- decreased secretion of K+ and H+ (likely acidoxic)

Question 13

Describe the clinical pathology of hypoadrenocorticism: urinalysis

Answer 13

Azotaemia (increased urea and creatinine)
Hypoglycaemia
Decreased USG (Na in filtrate impairs ability to retain water)

Question 14

Describe the electrocardiogram of an animal with hypoadrenocorticism

Answer 14

Changes related to hyperkalaemia:
- bradycardia
- peaked T waves
- widened GRS complexes
- decreased P wave amplitude
- absent P waves
- ventricular asystole (failure to contract)

Question 15

how can hypoadrenocorticism be diagnosed?

Answer 15

ACTH stim test - no change in cortisol as adrenal cortex is destroyed

Question 16

Describe the treatment of hypoadrenocorticism

Answer 16

Mineralocorticoids - monthly injection
Glucocorticoids during acute crisis or times of stress