March 2002 National Symposium on Dermatomyositis

Commonly asked questions about dermatomyositis (DM) in dogs:

 

1.      What is dermatomyositis?

Dermatomyositis (DM) is a devastating inherited inflammatory disease of the skin and/or muscle, which most commonly afflicts Collies, Shetland Sheepdogs and their crosses.  The skin lesions consist of hair loss with or without skin redness, scaling and crusting of the face, ears, legs and tail tip.  One or more of these areas of the body may be affected.  In addition, some dogs may have muscular involvement.  Sometime this muscle involvement is so pronounced that it results in muscle atrophy.  Other cases may suffer from megaesophagus (enlarged food tube in the body) with the end result of aspiration pneumonia.  In milder cases the dogs may appear to be sloppy eaters, or have a strange high stepping gait.  Shetland Sheepdogs are fortunate because muscle involvement does not seem to be as common as with the Collie.  Most commonly dogs develop the skin lesions within the first few years of life but dogs as old as 8 years old have been reported to develop this problem.  It is thought that certain triggering factors such as stress may cause a dog to express the DM.  These triggering factors are thought to include such circumstances as a bad viral infection (i.e. parvo) and hormonal fluctuations (heat cycles).  In some cases no triggering factor has been identified.  Since this is a genetic problem, affected dogs should be spayed or neutered.  This will also help the dogs respond better to treatment.

 

DM is not an itchy problem unless a secondary infection is present.  So if your pet is itchy and it does not look like a secondary infection is present (bacteria or yeast) then your pet’s problem is probably not DM.  The only exception would be if you had a dog with DM and an underlying allergy.  This can occur but is not common.

 

NOTE:  Some people use the abbreviation DM to stand for diabetes mellitus (a type of diabetes) or demodex (a type of mite found on skin scraping).  When we use this abbreviation we are using it to represent the skin disease dermatomyositis.

 

2.      How is DM diagnosed? 

DM is diagnosed by taking the dog to a veterinarian and having a physical examination and a skin and muscle biopsy taken.

 

3.      When should I have my dog biopsied? 

If you have a Collie, Shetland Sheepdog or their cross with any of the problems or clinical signs listed above (part 1).

 

4.      What is involved with a biopsy? 

A biopsy is taken with either a local block (usually lidocaine), sedation and/or local block, or under general anesthesia.  A minimum of three pieces of tissue (skin and muscle) at least 6 mm in size are collected, placed in a formalin solution labeled individually and submitted to a pathologist for evaluation.  The areas of the biopsy are sutured and the sutures are usually removed in 10 to 14 days after the procedure.

 

 

5.      Where should the biopsies be submitted? 

The biopsies should be submitted to a pathologist who is trained in looking specifically at skin problems (dermatohistopathologist).  The one which is used by Texas A&M University College of Veterinary Medicine is the following:

Dermatopathology Specialty Service

P. O. Drawer 3040

College Station, TX  77843-3040

Phone (979) 845-3414 or (888) 646-5623

 

6.      How is DM treated in dogs? 

Several different treatment options are available and one of these treatments is usually used at a time.

 

  1. Steroids – In the past steroids were commonly used to treat DM but over time this drug can be hard on the liver and/or adrenal glands and result in secondary complications (recurrent infections from a suppressed immune system.)

 

  1. Trental® – Another option with less side effects is a drug called Trental® (pentoxifylline)  This is a drug that Dr. Rees, one of the dermatologists at Texas A&M College of Veterinary Medicine, is studying.  The only side effects which have been seen when using this drug are GI (vomiting and diarrhea).

These side effects have only been seen when the drug is not given with food or a generic brand of Trental® is used.  IT IS IMPORTANT TO ONLY USE THE BRANDNAME TRENTAL® if you decide to use pentoxifylline as your treatment option.  When generics have been used they have been found to be either ineffective (not helped the animal with the DM) or associated with the GI side effects (vomiting and diarrhea).

 

  1. Azathioprine (Imuran® ) – Azathioprine is the most common type of immunosuppressive drug that has been reported to be used to treat DM in dogs.  The use of this drug in dogs has been associated with several different side effects.  The main side effect that azathioprine causes is bone marrow suppression (decreased red blood cell count, decreased white blood cell count, decreased platelet count).  Other side effects of azathioprine in dogs include vomiting, diarrhea (most common side effect, may have blood in stool), hypersensitivity reactions (especially the liver), an inflamed pancreas, skins rashes and hair loss.  These dogs need to be closely monitored by a veterinarian and periodic bloodwork performed on them (initially every 2 weeks) to make sure that the dog is not having a problem with the azathioprine.

 

  1. Immunostimulant drugs – Immunoregulin® is a product of a kind of killed bacteria (Propionibacterium acnes) which is injected in the vein during set periods of time (initially twice weekly, then weekly then monthly).  Side effects occasionally occur after the injection and include lethargy, increased body temperature, chills and decreased appetite.  Anaphylactic shock reactions have also been reported.  If the drug is given outside of the vein then local tissue inflammation (swelling) has been reported.  Long term toxicity studies have demonstrated inflammation of the liver (hepatitis), GI signs (vomiting, diarrhea), decreased appetite, malaise (feeling poorly), fever, increased water consumption and acidosis.

 

  1. Antioxidants – The most common antioxidant which has been to treat DM is Vitamin E.  Some have used it topically but most veterinarians use it systemically (give a tablet or capsule by mouth).  If used at the dose reported in the literature then no side effects have been reported.  This treatment has not been evaluated scientifically in a large number of dogs.  Contact your veterinarian for recommendations on the appropriate dose of Vitamin E to use on your dog.

 

7.      How long will my DM dog need to be treated?

This is a gray area.  We do not know for sure.  Some dogs need 3 to 6 months of treatment and do fine whereas other dogs need life long therapy.  The length of treatment varies according to the individual dog and the severity of the disease.

 

8.      How is DM genetically expressed or passed on?

We do not know but we have seen this problem in certain breeding lines so we know that it is an inherited problem.  The exact mode of inheritance is not known.  This is the reason for the genetics study that we are performing at Texas A&M College of Veterinary Medicine.

 

 

Dr. Christine Rees

Texas A & M University