Addison’s Disease: The Great Pretender

Hypoadrenocorticism — Addison’s disease — is the opposite of Cushing’s: the adrenal glands fail to produce enough cortisol and, usually, aldosterone.

It is called the great pretender because the early signs are vague, intermittent, and identical to a dozen commoner problems. Many dogs are unwell on and off for months before the diagnosis is made.

The signs

Chronic and intermittent — the version that gets missed:

• Lethargy that comes and goes
• Waxing and waning appetite
• Intermittent vomiting and diarrhoea
• Weight loss
• Weakness
• Shaking or trembling
• Increased thirst and urination
• A dog who is “off” repeatedly, improves with supportive treatment, then relapses

The pattern that should raise suspicion: a young to middle-aged dog with recurrent unexplained digestive upsets and lethargy, who responds to fluids and then relapses weeks later.

Stress makes it worse. Signs frequently appear or intensify around kennelling, travel, house guests, thunderstorms or a change in routine — because cortisol is the stress hormone, and these dogs cannot produce it.

The Addisonian crisis

The emergency presentation, and it can be the first sign.

• Sudden collapse
• Profound weakness
• Severe dehydration
• Vomiting and diarrhoea
• A slow heart rate, which is unusual in a collapsed dog and is a significant clue
• Shock
• Low body temperature

This is caused by dangerously low blood sodium and high potassium, and the high potassium affects the heart. It is life-threatening and needs immediate treatment.

Any collapsed dog is an emergency, but a young adult dog who collapses with a slow heart rate is a strong candidate.

Who gets it

• Young to middle-aged dogs, typically four to five at diagnosis
• Female dogs are over-represented
• Breeds: Standard Poodles, Portuguese Water Dogs, Bearded Collies, Nova Scotia Duck Tolling Retrievers, Great Danes, Rottweilers, West Highland White Terriers and Wheaten Terriers. There is a known genetic component in several
• Dogs on long-term steroids that are stopped abruptly, which causes an iatrogenic version. This is why steroids are always tapered

Diagnosis

Screening bloodwork typically shows a low sodium and a high potassium, giving a reduced sodium-to-potassium ratio. Also common: raised kidney values, low blood glucose, and an absence of the expected stress leukogram in a sick dog.

Atypical Addison’s — where only cortisol is deficient and electrolytes are normal — is harder still, because the classic bloodwork clue is missing.

The definitive test is the ACTH stimulation test: measuring cortisol before and after an injection of stimulating hormone. In Addison’s, cortisol is low and stays low.

Baseline cortisol is sometimes used as a screen — a normal result effectively rules it out, a low one needs the stimulation test to confirm.

Treatment

Lifelong hormone replacement, and it works very well.

Mineralocorticoid replacement, either:

• A monthly injection (DOCP), given at the practice or at home after training, with periodic electrolyte monitoring to fine-tune dose and interval, or
• A daily tablet (fludrocortisone)

Glucocorticoid replacement — usually a low daily dose of prednisolone. Many dogs on injectable therapy need this alongside; some on fludrocortisone do not.

The crucial part: the dose goes UP at times of stress.

Because these dogs cannot mount their own cortisol response, they need extra during:

• Illness or injury
• Surgery or anaesthesia
• Boarding or kennelling
• Travel
• House moves
• Fireworks, thunderstorms
• Any significant upset

Your vet will give you a protocol for increasing the dose. Have it written down, and make sure anyone caring for your dog has it too.

Monitoring

• Electrolytes checked regularly — frequently at first, then every three to six months once stable
• Weight and body condition
• Appetite, energy, thirst and urination
• A diary, particularly around dose adjustments

Signs of under-treatment: lethargy, poor appetite, vomiting, weakness — the original signs returning.

Signs of over-treatment with glucocorticoid: increased thirst, increased appetite, panting, a pot-bellied appearance — essentially Cushing’s signs.

Both are reasons to ring, not to adjust the dose yourself.

Living with it

An ID tag or collar tag stating the dog is Addisonian is genuinely worth having. If your dog collapses while someone else has them, that single piece of information changes the emergency treatment.

Keep the written protocol — medication, doses, stress-dose instructions, and your vet’s number — where anyone can find it.

Minimise unnecessary stress. A predictable routine matters more for these dogs than for most.

Tell any vet who treats them, including out-of-hours practices, before any procedure.

Insurance, if you have it. Lifelong medication and monitoring is an ongoing cost, and Addison’s is usually diagnosed young enough that it will be excluded from any policy taken out afterwards.

Feeding is generally normal — there is no special Addison’s diet — though dogs recovering from a crisis or experiencing digestive signs may need bland food temporarily.

Prognosis

This is the genuinely good news.

Addison’s is one of the most satisfying conditions in veterinary medicine — a dog who has been vaguely unwell for months becomes entirely normal on treatment, and life expectancy with good management is close to normal.

The barriers are getting the diagnosis and remembering the stress dose. Once those are handled, most Addisonian dogs live ordinary lives.

The one-line version

If your young or middle-aged dog has repeated bouts of being “off” — vomiting, lethargy, poor appetite — that improve and come back, ask your vet specifically about Addison’s.

It is the disease that hides behind a dozen ordinary-looking episodes, and the dogs who are diagnosed early are spared a crisis.