Canine: Hypoadrenocorticism Flashcards
Hypoadrenocorticism can be either Primary or Secondary, what is the difference between these two?
Primary (95%+) = Addison’s Disease
- Immune-mediated cause
- Glucocorticoid + Mineralocorticoid deficiency (low cortisol + low aldosterone)
Secondary (<5%)
- Iatrogenic, Idiopathic or Pituitary neoplasia: leading to ACTH deficiency
- Glucocorticoid deficiency only (only low cortisol)
What is the age range and median age of dogs, which you can see Addison’s disease (Primary Hypoadrenocorticism)?
3 months - 14 years
The median age is 4 years old
Is there a breed disposition with Addison’s disease (Primary Hypoadrenocorticism)?
Yes, mostly purebreds (70%+) But can happen in any breed - Great Dane - Westie - Rottweilers - Wheaten terrier - Standard poodles - Beardies - Portuguese Water Dogs
What are the historical features of Hypoadrenocorticism in dogs?
- Non-specific illness
- Chronic
- Lethargy and anorexia (95%+)
- Vomiting (80%)
- Weight loss, waxing and waning, diarrhea (50%)
- Shaking, PU/PD (30%)
Owners will report these signs before seeking medical attention as the dog tends to recover on its own
What are the clinical features of Hypoadrenocorticism in dogs?
By the time a vet is seen, the following clinical signs are commonly noted as the dog is more severely ill:
- Depression/ lethargy, weakness
- Dehydration
- Shock
- Hypothermia
- Bradycardia
- Melena
- Trembling/ shaking
- Abdominal pain: will lead you to suspect pancreatitis
What Hematology results are expected with a dog suffering from Hypoadrenocorticism?
- RBC’s, Eosinophils and Lymphocytes
Most dogs have a reverse stress leucogram, due to the lack of glucocorticoid production
- RBCs: MOST are anemic (mild to severe depending on chronicity) but some are so dehydrated they have a higher PCV (erythrocytosis)
- Normal eosinophils
- Normal lymphocytes
note: in a normal stressed/ ill dog, cortisol will decrease eosinophils and lymphocytes (eosinopenia and lymphopenia), but because cortisol is lacking you don’t see a reduction in these cells and that is important!
What Biochemistry results are expected with a dog suffering from Hypoadrenocorticism?
- Azotemia + Hyperphosphatemia (80%+)
- Mild increased ALT and ALP
- Hypoglycemia (uncommon but can be severe): related to cortisol deficiency
- Hypoalbuminemia + Hypocholesteremia: due to losses in the gut
Due to aldosterone deficiency, you will see
- Hyperkalemia + Hyponatremia
- Hypochloremia: due to hyponatremia
- Hypercalcemia: cortisol deficiency leads to reduced Calcium excretion in the kidneys
You are presented with a dog that has non-specific clinical signs of illness, and biochemistry shows Hyperkalemia + Hyponatremia.
Because many disease states can have these signs, what should you look at to narrow down the differential list?
Na:K ratio
- Na:K ratio between 20-24 = renal disorder > other diseases > Hypoadrenocorticism
- Na:K ratio between 15 - 19 = renal disorder > Hypoadrenocorticism > other diseases
- Na:K ratio is below 15 = Hypoadrenocorticism
What general screening tests and more specific tests can be done to evaluate the presence of Hypoadrenocorticism?
- Hematology + Biochemistry
- Urinalysis
- ECG: especially if the dog is bradycardic. Most dogs will not have a predicted ECG change based on the level of hyperkalemia, and thus ECG is not a good indicator of K+ levels
- Radiography: might have Megaesophagus, Microcardia, Reduced pulmonary vasculature, Microhepatica
- U/S of adrenals: looking for an adrenal gland < 0.32 cm to support the presence of Hypoadrenocorticism. Due to the immune-mediated attack on the adrenal gland, you will get size-reduction
- ACTH stimulation test
An older dog with non-specific, less severe signs of illness (less lethargy, vomiting, diarrhea etc.) presents with Hypocortisolemia ONLY and no electrolyte disturbance, what can you do to narrow down your DDx? Could this be Hypoadrenocorticism?
Yes this could be a dog that presents in a small subset of Primary Hypoadrenocorticism
- Perform an ACTH stim test to rule in/out Hypoadrenocorticism
What would you expect to see on Urinalysis with a dog suffering from Hypoadrenocorticism?
- Isosthenuric or Hyposthenuric (equal to low SG): this is because the animal will have Hyponatremia, and therefore will find it difficult to concentrate its urine
All other parameters can be normal
You are presented with a dog that you suspect to have Hypoadrenocorticism, and you would like to do an ACTH stim test to confirm, however the Owner lets you know that she gave her dog a dose of prednisolone yesterday as she had it in her home from another vet visit. What test can you do or what parameter can be measured since the dosing of prednisolone will interfere with the cortisol levels
- Measure Aldosterone levels instead
Note: or can wait 2 weeks and test cortisol levels/ do a ACTH stim test
You diagnose a dog with Hypoadrenocorticism, what is the treatment and prognosis?
Intensive therapy:
- IV Fluids to address dehydration + electrolyte disturbances. 0.9% saline +/- 5% glucose if hypoglycemic. rate is dependent on degree of dehydration or if the animal is in shock
Dogs in shock will receive a rapid bolus and then a slow rate after this
- Hormones replacement:
Glucocorticoid only = Dexamethasone. This won’t interfere with cortisol levels and therefore can be given before an ACTH stim test
Mineralocorticoid + Glucocorticoid = Hydrocortisone. This WILL interfere with Cortisol levels. This is her preference once an ACTH stim test is done
Prognosis = excellent
But will require lifelong treatment
You are presented with a dog where you suspect Hypoadrenocorticism, however the dog is in shock and requires immediate attention, what supportive treatment is needed?
- 0.9% saline +/- 5% glucose if hypoglycemic
At a rate of 20 - 40 ml/kg for 1-2 hours (can go to 60-80 ml/kg/hr if needed) - Dexamethasone: won’t interfere with ACTH stimulation test at 0.5-2 mg/kg IV as a bolus
- Once the patient is stable, and an ACTH stim test is done, provide a maintenance rate of 0.9% saline with 0.5-0.625 mg/kg/hr of Hydrocortisone. Give for 12 to 24 hours
caution: normal saline must be used when giving hydrocortisone as it will precipitate in LR’s
When treating a dog that has Hypoadrenocorticism, with Hydrocortisone, what must you be careful of?
- Hydrocortisone will have a rapid effect on the dog
You want to administer Hydrocortisone with maintenance fluid rate because you want potassium and sodium levels to normalize SLOWLY
A rapid increase in Sodium can lead to osmotic demyelination of nervous tissue
