Dear Dr. Thompson: In January, 2011, I adopted a female sheltie from the local dog warden. She was shaved like a lion. Six months later her fur had not grown in fully with bald spots and still no fur on her tail (just a tuft on the end). My vet checked her for Addison's, Cushing's, and a thyroid deficiency; all came back negative.
She was then treated for mites. My vet is at a loss as to why her fur has not fully grown back. Do you have any thoughts on what the problem is?
It sounds like you and your veterinarian have taken a number of appropriate steps to determine the cause of your dog's hair not re-growing, which is called alopecia. By far the most common causes in a dog this age would be an underactive thyroid gland or problems with the adrenal glands, because the hormones produced by those glands directly affect the hair cycle.
There may be some tests that your veterinarian already ran that you did not mention, but I might suggest a couple other options before more involved diagnostics are undertaken.
You mention she was treated for mites, but occasionally an overgrowth of a skin mite called demodex can result in hair loss. While common in puppies, the disease in older dogs would almost always be secondary to another disease that is suppressing normal immune function, and I would have expected other symptoms to be present.
The mite is found with a deep scraping of the skin with a scalpel blade and evaluated under a microscope. Dogs with this skin mite overgrowth are typically itchy and have infections that accompany this condition, so I think it is unlikely to be the source of her alopecia.
Ringworm is a fungal skin infection that lives in the hair itself and can lead to patchy hair loss. People expect to see a circular lesion similar to the presentation in people that led to its name, but it is not a typical symptom seen in pets.
Occasionally, a simple test with a special blacklight can detect the fungus in the hair, which will fluoresce a candy apple green. More commonly it requires plucking some hairs and placing them in a special culture medium to grow for a couple of weeks. Some degree of itching normally accompanies ringworm, but not always, so it should not be ruled out as a possibility.
Once you have eliminated those diseases with some simple tests, less common causes should be considered. Other hormonal diseases can cause an arrest of the hair cycle and some more involved testing would be needed. The precursors to the stress hormone cortisol are not detected on the standard test for Cushing's disease in dogs and could be causing your pet's problems.
We are also seeing more dogs with increased levels of estrogen and estrogen precursors even in spayed females and neutered males. Often this is a byproduct of obesity in pets, but not always.
Normally increased thirst and urinations accompany both of these diseases, but it can be subtle. An excellent test exists for these conditions from the University of Tennessee and treatment can be very simple and economical.
If many of these hormonal and infectious causes have been eliminated, a skin biopsy sent to a veterinary dermatopathologist might be indicated.
If she is younger than six months of age, an inherited condition called ischemic dermatopathy might be the source. Shelties have a sub-type labeled dermatomyositis (DM), but it is unusual and will often have other symptoms that accompany the disease.
It may be as simple as post-clipping alopecia, which halts the hair cycle, and some treatments could be considered if the alopecia is severe, but these usually have limited efficacy.
It sounds as though you and your veterinarian have taken the appropriate steps to this point and I hope you have success in getting to the root of the problem. Good luck.
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