Canine Hypoadrenocorticism (Addison's)

Key tip offs (4)

-.bradycardia in the face of cardiovascular collpase

-severe dehydration with USG < 1.030

-Na: K ratio <27

-Episode brought on by stress

Diagnostic test of choice

ACTH stimulation test

Critical therapies (basic list)

-rapid infusion of iv fluids (0.9% NaCl)

-treat severe hyperkalemia → calcium gluconate, regular insulin, dextrose, bicarb, corticosteroids

Cause and and loss of what adrenal products

-inadequate adrenal production of glucocorticoids and mineralocorticoids

-most commonly idiopathic adrenocorticol atrophy

MOA for glucocorticoids and mineralocorticoids

-glucocorticoid: needed by every organ int he body for homeostatic function and glucose regulation

-mineralocorticoid: deficiency leads to an inability to retain sodium or to excrete poassium and hydrogen resulting in hypotonic dehydration, hyperkalemia, and metabolic acidosis

What is lacking in production for an “atypical” Addison’s patient

-a deficiency in either glucocorticoids OR mineralocorticoids

Typical signalement

-middle aged: 3-7 years, mean 4 year old, 70% female

-breed predilections: black standard poodle, portuguese water dog, great dane, rottie, westie, wheaton terrier

Clinical signs for acute Addison’s

-hypovolemic shock with weakness and vomiting (maybe hematemesis)

Clinical signs for chronic Addison’s

-may see worsening of signs during stressful periods

-PU/PD

-non specific and can be mistaken for renal, GI disease, or pancreatitis

Labwork clinical signs/PE

-hyperkalemia, hyponatremia (Na:K ration < 27)→ hypochloremia, hypercalcemia, hypoglycemia

-pre renal azotemia secondary to severe dehydration, can be confused with renal failure

-low specific gravity <1.030

-absence of a stress leukogram on CBC

-GI blood loss (decreased albumin from PLE) and increased BUN from GI bleeding

-bradycardia and ECG changes consistent with hyperkalemia (tall tented t wave, diminished to absent p waves, prolonged p-r interval, wide QRS complexes)

-can see megaesophagus, microcardia, small adrenal glands on U/S

Diagnostic Confirmation

-ACTH stim test of choice: measure serum cortisol before and after admin of ACTH gel or synthetic ACTH

-normal dogs generally have a post stim cortisol levels > 10 ug/dl. Post stimulation levels < 2 ug/dl is considered diagnostic and most patients are <1 ug/dl

-any steroid admin other than dexamethasone can invalidate the test

Acute presentation tx

-restore blood volume: rapid admin of fluids. 60-90 ml/kg as shock dose or incremental boluses of 10-30 ml/kg until resuscitation. Avoid overly rapid increases in sodium by fast iv fluid admin. Will restore perfusion to organs like the kidneys and reduce hyperkalemia through increased GFR and dilutional effects. 0.9% NaCl

-treat hyperkalemia: if cardiac abnormalities persist despite fluid therapy. Calcium gluconate for temp cardio protection in addition to glucose, insulin or bicarb to promote intracellular shift of potassium

-IV glucocorticoids: dexamethasone sp

-begin maintainence of corticosteroids and mineralocorticoids

Treatment of chronic presentation

-lifetime corticosteroid maintenance: prednisone or prednisolone, starting at 0.5 mg/kg/day as supraphysiologic dose for one week and taper down to maintainance (0.1-0.2 mg/kg/day). Give 2-4x maintainance dose at times of stress

-lifetime mineralocorticoid maintenance: oral fludrocortisone daily or injectable DOCP every 3-4 wks