Tier 1 — must know Canine Endocrine Emergency

Addison's disease

Hypoadrenocorticism · high exam frequency · internal medicine + emergency overlap

⏱ 2–3 min read · Topic 1 of 6

Practice Qs

Traps

High

Exam freq.

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Your status

Study mode

Quick anchor

Trigger

Sick dog + bradycardia

First step

IV fluids first

Confirm

ACTH stim test

Trap

Normal K does not rule it out

Exam core — read this first

Sick dog + bradycardia → think Addison's

Unstable patient → IV fluids first (0.9% NaCl)

Stable patient → ACTH stimulation test

Safe steroid before testing → dexamethasone only

Clinical mechanism — only what matters

↓ Aldosterone → Na loss + K retention → hypovolemia + bradycardia

↓ Cortisol → poor stress response → collapse under stress

You do not need deeper pathophysiology here. Just know how the hormone deficits create the clinical clues NAVLE tests.

Pattern recognition

Core pattern

Sick dog + bradycardia Collapse / weakness Vomiting + diarrhea

Supporting clues

Waxing / waning history Weight loss Pale or tacky mucous membranes Young–middle-aged female Shaking or muscle weakness

NAVLE trigger: The mismatch is the signal. Very sick dogs are usually tachycardic. If the patient looks shocked but the heart rate is slow, think hyperkalemia and push Addison's high on the list.

Decision core — what NAVLE actually asks

Unstable patient — hypotensive, obtunded, bradycardic

→ IV fluid resuscitation first (0.9% NaCl) · do NOT delay for diagnostics · stabilize before anything else

Stable patient — weak, GI signs, abnormal labs

→ Proceed to ACTH stimulation test to confirm diagnosis · then start appropriate therapy

Safe steroid if giving before ACTH test

→ Use dexamethasone only — it is NOT detected by cortisol assay and will not invalidate the test

Key interpretation

Sodium

↓ Low

Aldosterone deficiency → Na wasting

Potassium

↑ High

K retention → bradycardia risk

Na:K ratio

< 27

Classic high-yield pattern

Azotemia

Prerenal

From hypovolemia — not primary renal failure

Urine SG

Normal / not dilute

Helps separate from CKD

ACTH stim

Flat cortisol response

Definitive confirmation

⚠ Normal potassium does NOT rule out Addison's disease. Atypical hypoadrenocorticism can have normal electrolytes.

Treatment

Acute

0.9% NaCl IV bolus + dexamethasone sodium phosphate IV

Stabilize hemodynamics first. Dexamethasone is safe before ACTH testing.

Chronic

DOCP (Percorten-V) every 25–30 days + daily prednisone

DOCP = mineralocorticoid replacement · prednisone = glucocorticoid replacement.

Alt.

Fludrocortisone acetate twice daily + prednisone

Alternative option. Usually needs more dose adjustment over time.

NAVLE traps — where students lose marks

Bradycardia in a sick dog is not normal

This is the main red flag. Shocked dogs are usually tachycardic — bradycardia points to hyperkalemia and Addison's.

Do NOT wait for ACTH results before starting IV fluids in an unstable patient

Stabilization comes first. Diagnosis follows once the patient is safe.

Normal potassium does NOT rule out Addison's disease

Atypical Addison's can present with normal electrolytes. Clinical suspicion still matters.

Prednisone before ACTH stimulation test will interfere with results

Use dexamethasone instead. Prednisone cross-reacts with cortisol assays.

Differentials — how to separate these on NAVLE

Fast separator: Addison's is the one that gives you a very sick dog with bradycardia. Most other collapse or shock differentials are normal heart rate or tachycardic.

Disease	Heart rate	Na:K ratio	Key separator
Addison's (typical)	↓ Bradycardia	< 27	Bradycardia + low Na:K
Addison's (atypical)	↓ Bradycardia	Normal	Normal electrolytes do not exclude it
Chronic kidney disease	Normal / ↑	Normal	Dilute urine / loss of concentrating ability
Primary GI disease	Normal / ↑	Normal	No classic electrolyte pattern
Septic shock	↑ Tachycardia	Normal	Fever, source, tachycardia

Mini cases — apply the decision framework

Next best step

5yr MN Standard Poodle presents collapsed and obtunded. HR 44 bpm, BP 65/40 mmHg. Owner reports intermittent vomiting for one week. Labs are pending. What is the most appropriate immediate next step?

Interpretation

4yr SF Labrador. 2-month waxing/waning GI signs. Bloodwork: Na 126 mEq/L, K 6.9 mEq/L, BUN 42 mg/dL, Creatinine 1.4 mg/dL, USG 1.018. What is the most likely diagnosis?

Trap case

6yr SF Labrador. Chronic intermittent vomiting. Serum electrolytes are normal. The clinician concludes Addison's disease has been ruled out. Is this reasoning correct?

Clinical application tools

Use these only as support. They reinforce the real management logic for Addisonian patients.

Sodium calculator Fluid calculator Potassium calculator Fluid bolus

30-second revision

Key trigger signSick dog + bradycardia

Key labsNa↓ K↑ Na:K < 27

First step (unstable)IV fluids — 0.9% NaCl

Safe steroid pre-testDexamethasone only

Confirm diagnosisACTH stimulation test

Chronic RxDOCP + prednisone

Critical trapNormal K ≠ rules out Addison's

Practice questions

Pre-built NAVLE-style · Addison's disease

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Q1Pattern recognition

A 4yr FS Standard Poodle presents with acute collapse, vomiting, and profound weakness. On examination, the dog is depressed and poorly perfused, but the heart rate is only 48 bpm. Which diagnosis should rise sharply on your differential list?

ASeptic shock

BHypoadrenocorticism

CPrimary GI foreign body

DCardiogenic pulmonary edema

EAcute pancreatitis

Q2Next best step

A 5yr MN Standard Poodle presents collapsed and obtunded. HR is 44 bpm, BP 65/40 mmHg. The owner reports intermittent vomiting for one week. Bloodwork is pending. Which of the following is the most appropriate immediate next step?

APerform ACTH stimulation test before initiating treatment

BStart IV fluid resuscitation with 0.9% NaCl

CAdminister prednisone IV for suspected cortisol deficiency

DGive fludrocortisone orally for mineralocorticoid replacement

EObtain abdominal ultrasound to rule out splenic mass

Q3Interpretation

A 4yr SF Labrador Retriever has a 2-month history of intermittent vomiting, lethargy, and weight loss. Serum chemistry: Na 126 mEq/L, K 6.9 mEq/L, BUN 42 mg/dL, Creatinine 1.4 mg/dL. Urinalysis: USG 1.018. Which interpretation is most consistent with these findings?

AChronic kidney disease with secondary electrolyte derangement

BHypoadrenocorticism with prerenal azotemia

CProtein-losing nephropathy

DPrimary hyperaldosteronism from adrenal adenoma

ECentral diabetes insipidus with hyponatremia

Q4Treatment

A 7yr MN Beagle is diagnosed with hypoadrenocorticism. ACTH stimulation test: baseline cortisol 0.8 µg/dL, post-ACTH cortisol 1.1 µg/dL. He is now clinically stable after emergency treatment. Which describes the correct long-term management?

APrednisone alone at anti-inflammatory doses is sufficient

BFludrocortisone alone provides both mineralocorticoid and glucocorticoid replacement

CDOCP injections every 25–30 days plus daily prednisone

DOral hydrocortisone and spironolactone combined

EDexamethasone long-term — preferred over prednisone for chronic use

Q5Differential

A 5yr SF mixed breed dog presents with acute collapse. HR is 42 bpm. Serum Na 124 mEq/L, K 7.1 mEq/L. A colleague suggests this could be chronic kidney disease causing the electrolyte changes. Which finding most helps differentiate hypoadrenocorticism from CKD in this case?

AElevated BUN and creatinine

BUrine specific gravity of 1.018

CLow serum sodium

DAge and breed of the patient

EPresence of vomiting

Q6Trap question

A 6yr SF Labrador has a 3-month history of intermittent vomiting and lethargy. Serum electrolytes are within normal reference ranges. Na:K ratio is 31. The attending veterinarian concludes that hypoadrenocorticism has been excluded based on the normal electrolytes. Which statement is most accurate regarding this conclusion?

AThe conclusion is correct — normal Na:K ratio effectively rules out Addison's disease

BThe conclusion is incorrect — atypical Addison's can present with normal electrolytes

CThe conclusion is correct — only typical Addison's occurs in dogs over 5 years

DThe conclusion is incorrect — potassium alone is not sufficient to assess

EThe conclusion is correct if repeated electrolytes also remain normal