Small animal endocrinopathies Flashcards
Canine hypoadrenocorticism, diabetes
What are the 3 zones of the adrenal cortex and what does each produce?
- Glomerulosa: mineralocorticoids (aldosterone)
- Fasciculata: glucocorticoids
- Reticularis: Androgens
What is a potential, but less common, pathological process of adrenal insufficiency?
Mineralocorticoids abnormal first, and then progress to glucocorticoid deficient i.e. moving inwards starting at the glomerulosa
What stimulates the release of aldosterone?
- RAAS
- Decreased BP detected by baroreceptors in macula densa in distal tubule, also cardiac and arterial baroreceptors
- Renin released from kidneys -> angiotensin release -> aldosterone release
- Also increased potassium concentratione
What are the functions of aldosterone?
- Acts on distal tubule cells, and CD to increase reabsorption of Na and Cl and therefore water
- Stimulates K+ secretion into tubular lumen
- Stimulates secretion of H+ in exchange for k+ in collecting tubules and so regulates acid/base
What are the different types of hypoadrenocorticism?
- Primary/Addison’s
- Secondary
- Iatrogenic
What are the potential causes of primary hypoadrenocorticism?
- Idiopathic atrophy (immune mediated, associated with other endocrinopathies)
- Iatrogenic (e.g. drugs, mitotane, trilostane), or surgery )bilateral adrenalectomy)
Describe the pathophysiology of primary hypoadrenocorticism
- Deficiency of glucocorticoids and mineralocorticoids
- Occurs with loss of 85-90% of adrenal cortex
- CRH and ACTH increase due to loss of negative feedback
Describe the pathophysiology of secondary hypoadrenocorticism
- Deficiency of ACTH
- Only cortisol deficiency, electrolytes normal
- Rare
Describe the pathophysiology of iatrogenic hypoadrenocorticism
- Exogenous steroids lead to adrenal atrophy
- Cortisol deficiency only
- Patient may have signs of Cushing’s syndrome
- Patient may develop signs of Addison’s if steroids abruptly discontinued
Outline the signalment of canine hypoadrenocorticism
- Young-middle aged dogs (4-6yrs)
- 70% females
- Standard poodles, bearded collies, Great Dane, Rottweiler, WHWT, soft coated wheaten terrier (but any breed possible)
- Some inheritance
In relation to hypoadrenocorticism, what should be considered inthe Nova Scotian Duck tolling retriever?
Juvenile Addison’s at 5mo-1yr old, immune mediated disease
What are the pathophysiological effects of aldosterone deficiency?
- Loss of Na+, Cl- and H20
- Retention of K+ and H+
- Pre-renal azotaemia
What are the pathophysiological effects of glucocorticoid deficiency
- Decreased stress tolerance
- GI signs, e.g. haemorrhagic gastroenteritis
- Weakness
- Appetite loss
- Anaemia
- Impaired gluconeogenesis
Describe the common clinical history of a dog with hypoadrenocorticism
Waxing and waning with non-specific signs worsened by stress
- Anorexia, V/D, lethargy, depression, weakness
- Shivering, weight loss, PUPD, abdominal pain
- Should consider hypoA in any animal with waxing and waning signs esp GI
What are the signs of acute hypoadrenocorticism?
- Marked hypovolaemia and azotaemia
- Paradoxical relative bradycardia (hyperkalaemia)
- Collapse, extreme weakness, hypothermia, recent history of V/D
- Abdo pain, melena (dark black tarry faeces) may feature,
What oher condition might signs of an Addisonian crisis resemble?
Pancreatitis
What are the common biochemical features of hypoadrenocorticism?
- Hyperkalaemia
- Hyponatraemia
- Hypocholridaemia
- Na:K ratio <23
- Hypercalcaemia
- Electrolyte changes may lag behind clinical signs and history - if normal but still suspicious repeat biochem in a few months
What features of a complete blood count are common in hypoadrenocorticism?
- Lack of stress leukogram (no neutrophilia, eosinopaenia and lymphopaenia)
- Anaemia
- Lymphocytosis
- Eosinophilia
What features of biochemistry and urinalysis are common in hypoadrenocorticism?
- Azotaemia
- Decreased USG
- Hypercalcaemia
- Hypoglycaemia
What features may be seen on thoracic radiographs in hypoadrenocorticism?
Megoesophagus (but <1%)
Explain megaoesophagus in hypoadrenocorticism
- May be muscle weakness, decreased Na and K = decreased membrane potential, decreased cortisol also associated with muscle weakness, reversible with treatment
What features may be seen on an electrocardiogram in hypoadrenocorticism?
- Bradycardia
- Peaked T waves
- Widened QRS complexes
- Decreased P wave amplitude/complete disappearance
- Ventricular asystole
What are the definitive diagnostic tests for hypoadrenocorticism?
- ACTH stim test
- Basal cortisol
What results would be expected in an Addisonian dog on an ACTH stim?
Flatline cortisol following ACTH administration i.e. no increase in cortisol production