Tuesday, December 28, 2010

Common Misdiagnoses (Part 1)

by Jennifer Coates, DVM

Veterinary (and human) medicine is at least as much of an art as it is a science.  What does this mean for dog owners?

You should consider any diagnosis that your dog receives to be a “work in progress.”  

No vet would intentionally misdiagnose a dog, but certain diseases are notoriously difficult to pin down.

If you have been told that your dog has any of the following conditions (or any health problem for that matter), but he is not responding to treatment as expected, the disease is progressing in an unusual manner, or your gut is telling you that something just isn’t right, talk to your vet.  He or she should be open to reevaluating the situation.  If not, get a second opinion.

Skin Problems

Dermatological conditions can be frustrating to diagnose.  The skin responds to virtually any insult – bacterial infection, parasites, immune disorders, etc. – with the same symptoms, so diagnostic tests are usually necessary to reveal the cause.

Remember though that no test is perfect, false negatives and false positives do occur, so if lab results do not mesh with a dog’s clinical picture they need to be questioned.

To confuse the situation even more, some skin problems, like bacterial or yeast infections, almost always develop because there is an underlying condition that has disrupted the skin’s normal defensive mechanisms.

If your dog has been diagnosed with a skin infection and it either doesn’t go away with treatment or comes back when treatment is stopped, you and your vet will need to start looking for the reason why.

Allergies are a common underlying cause of recurrent skin problems in dogs. 

But, the only way to know for sure that a dog has allergies and what his triggers are is through allergy testing.  Intradermal allergy tests are best.  Blood testing is another option, but the results are not as accurate.

Many vets (myself included) are willing to diagnose allergies without allergy testing after ruling out other common causes of itchy skin, and this is appropriate as long as owners are aware of the plusses and minuses of this approach.  If, however, a dog’s condition doesn’t respond to treatment as expected, the initial diagnosis should be reevaluated.

Hormonal Diseases

Getting to the bottom of hormonal diseases can also be difficult.  Hypothyroidism is an excellent example.

A low total thyroid level on blood work alone is not sufficient to reach a diagnosis of hypothyroidism.  

Dogs must also show some of the typical signs of the disease:  weight gain, low energy levels, cold intolerance, hair loss, or skin problems, and these issues should improve once thyroid supplementation has been started.

A condition call sick euthyroid syndrome can also cause thyroid hormone levels to fall, but this is not true hypothyroidism and treatment with thyroid supplements is not beneficial.

Cushing’s disease is another tough one.  

A vet might suspect its presence after finding elevated alkaline phosphatase (ALP) levels on routine blood work or high cortisol levels on a urine test, but either a low dose dexamethasone suppression test or an ACTH stimulation test is necessary to confirm the diagnosis.

However, such advanced testing may not be necessary early in the course of the disease because in most cases, Cushing’s disease shouldn’t be treated unless a dog has symptoms that are starting to interfere with its quality of life (e.g., increased appetite, thirst and urination, skin and coat problems, or a pot-bellied appearance).  This is another situation where a big-picture approach is necessary.

Addison’s disease is probably even more frequently misdiagnosed than is Cushing’s.  

The typical symptoms – vomiting, diarrhea, weakness, collapse – can occur as a result of whole laundry list of health problems.  In many cases, a fairly distinctive change in blood electrolyte levels occurs with Addison’s disease, but electrolytes are not always included in panels of routine blood work.  Also, not every victim of Addison’s has these electrolyte changes, so an ACTH stimulation test is required to determine whether or not Addison’s is responsible for a dog’s clinical signs.

In my next post, I’ll talk about how orthopedic diseases can be confused with one another and the devastating consequences that can result.


Jennifer Coates, DVM graduated with honors from the Virginia-Maryland Regional College of Veterinary Medicine in 1999.  In the years since, she has practiced veterinary medicine in Virginia, Wyoming, and Colorado.  She is the author of several books about veterinary medicine and animal care, including the Dictionary of Veterinary Terms: Vet-speak Deciphered for the Non-veterinarian

Jennifer also writes short stories that focus on the strength and importance of the human-animal bond and freelance articles relating to a variety of animal care and veterinary topics.  Dr. Coates lives in Fort Collins, Colorado with her husband, daughter, and pets.

Related articles:
Common Misdiagnoses (Part 2)
A Word on Second Opinions
It's Your Dog's Health!
Veterinary Drive-Thru: Coming Soon To A Veterinary Hospital Near You!
Does Your Vet Listen To You?
Help! My Dog Is Purple!
A Praise To Our Dog House DVM
A Word On Pain


  1. Thank you for this very informative post. There is a lot of information out there and it's hard to know who to trust sometimes.

  2. Dear Kristine. There is a lot of information and lot of conflicting opinions out there. It truly seems there are no ultimate truths at this time.

    In this respect life was easier under communists. There was an ultimate truth for everything and nobody dared to question any.

    I think that at this point in time most of it boils down to what your gut tells you.

    I do a lot of research and consider all different opinions but at the end, I am the one who has to figure out which one makes sense to me. Can I choose the wrong path? Certainly. But at least I'll know I did my darnest.

  3. Great information. Thank you so much for sharing.