Addison's Disease (Canine) — NAVLE Prep

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) ± dextrose if hypoglycemic

Stable patient → ACTH stimulation test

Safe steroid before testing → dexamethasone only

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

Severe hyperkalemic arrhythmia present

→ Continue aggressive stabilization and use IV calcium gluconate for cardioprotection

Key interpretation

Sodium

↓ Low

Aldosterone deficiency → Na wasting

Potassium

↑ High

K retention → bradycardia risk

Na:K ratio

< 27

Classic high-yield pattern

Glucose

May be low

Correct hypoglycemia if present

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. Electrolytes may be normal initially, and these patients still require monitoring because mineralocorticoid deficiency can develop later.

Treatment

Acute

0.9% NaCl IV bolus + dexamethasone sodium phosphate IV

Stabilize hemodynamics first. Dexamethasone is safe before ACTH testing, and correct hypoglycemia if present.

Rhythm

IV calcium gluconate if severe hyperkalemic arrhythmias are present

This is for cardioprotection while definitive stabilization continues.

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.

Whipworms can create a pseudo-Addison electrolyte pattern

Trichuris vulpis is a classic board-style mimic when the sodium and potassium pattern looks convincing.

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
Trichuris vulpis (whipworms)	Normal / ↑	Can be low	Pseudo-Addison mimic with GI parasite history
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

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?

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?

Q3Interpretation / differential

A dog with waxing and waning GI signs has hyponatremia and hyperkalemia. Which classic board-style mimic can create a pseudo-Addison pattern and should stay on your differential list?

Q4Trap question

A dog strongly suspected of atypical Addison's has normal sodium and potassium today. Which statement is most accurate?