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

High-yield takeaways

Start with the safest next step, then narrow the case using signalment, timeline, exam findings, diagnostics, and response to treatment.
Use the traps, differentials, and practice questions to rehearse NAVLE-style reasoning instead of memorizing isolated facts.
This educational study page is not a clinical protocol; confirm patient-specific decisions with current references and clinician judgment.

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

CBC pearlSick dog without stress leukogram

Confirm diagnosisACTH stimulation test

Chronic RxDOCP + prednisone

Critical trapNormal K ≠ rules out Addison's

Exam core — read this first

Sick dog + bradycardia → think Addison's

Crisis first → collapsed, hypotensive, bradycardic dog gets 0.9% NaCl before confirmatory testing

Stable patient → ACTH stimulation test

Safe steroid before testing → dexamethasone only

Emergency Triage Alert

Crisis First: Stabilize Before You Confirm

A collapsed, hypotensive, bradycardic dog is an emergency first and an endocrine workup second. Start 0.9% NaCl immediately; use dexamethasone if a steroid is needed before ACTH stimulation testing.

Monitoring Note

Secondary Monitoring

Addison's is not zoonotic, but chronic mineralocorticoid deficiency requires consistent electrolyte monitoring to prevent crisis.

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

CBC

No stress leukogram

Normal/increased lymphocytes or eosinophils in a sick dog support Addison's

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.

Pharmacology pearls

DOCP (Percorten-V)

Class: Mineralocorticoid

Logic: Replaces aldosterone

Board Pearl: Given IM/SC every ~25-30 days; only affects electrolytes, NOT cortisol.

Fludrocortisone

Class: Mineralocorticoid + Glucocorticoid

Logic: Dual replacement

Board Pearl: Oral daily dosing; often requires more frequent electrolyte monitoring than DOCP.

Dexamethasone

Class: Glucocorticoid

Logic: Acute stabilization

Board Pearl: Safe to give BEFORE ACTH stim; does not cross-react with cortisol assay.

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.

Postrenal obstruction can mimic hyperkalemic Addison's

A blocked dog can be bradycardic with hyperkalemia and azotemia. Check urination history and bladder size before anchoring.

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
Postrenal urinary obstruction	↓ possible	Variable / K high	Stranguria, anuria, large painful bladder, postrenal azotemia
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

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?

Q3Mimic trap / case drill

A 6yr MN mixed-breed dog presents for collapse and vomiting. HR is 52 bpm, pulses are weak, potassium is 7.2 mmol/L, sodium is mildly decreased, and creatinine is elevated. The owner says he has been straining to urinate all morning, and palpation reveals a large painful bladder. Which interpretation best prevents a NAVLE anchoring error?

Q4Trap question

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

Hypothyroidism