Dermatomyositis in Dogs

Usually affecting puppies, dermatomyositis is a genetic condition in some breeds of dogs that causes tissue inflammation and skin lesions. While it's not as common as other canine diseases, dermatomyositis is a serious condition. It is inherited by puppies from their parents and typically affects collies and Shetland sheepdogs, but it may also affect other breeds including the Pembroke Welsh corgi, Lakeland terrier, chow chow, German shepherd, and Kuvasz. While there is no cure for dermatomyositis, dogs with this disease can be treated for their symptoms to avoid further progression. Recognition of the condition can aid in early management, and therefore keep a dog with dermatomyositis comfortable for a longer period of time.

What Is Dermatomyositis?

Dermatomyositis is a genetic disease that causes dogs to develop inflammation in the skin, muscles, and blood vessels, which can also lead to severe symptoms like skin ulcerations and loss of muscle mass when the condition is chronic. This disease is also hereditary in humans. It is not fully understood yet, but veterinary professionals recognize it as an immune-mediated condition. Dermatomyositis causes a variety of symptoms, but skin lesions are most commonly seen.

This condition primarily affects puppies, as adult-onset dermatomyositis is rare. Puppies who exhibit symptoms of dermatomyositis seem to be more severely affected than adult dogs with this disease, and the most severe symptoms typically develop in the first year of a dog's life. Symptoms may appear as early as seven weeks of age but are typically seen by the time a puppy is six months old.

Symptoms of Dermatomyositis in Dogs

Most commonly identified by crusted and inflamed lesions on the face or ears, signs of dermatomyositis will typically involve either skin or muscle issues. The following are symptoms that dogs with this disease may experience:

Skin Lesions

The severity of dermatomyositis and its symptoms will vary from dog to dog, but skin lesions are the most common sign. These lesions may be mild, moderate, or severe. They can be painful and may even bleed or become ulcerated. Owners often initially report seeing sores on the face of their puppies, but early signs are often initially ignored or not noticed when mild. As the disease progresses, you may notice lesions on your dog's eyes, ears, lips, or tail. These areas may begin to heal and then redevelop in other places on the body.

Hair Loss

As a result of skin lesions, your puppy may experience hair loss in affected areas. Dogs may begin to lick at affected areas when they become painful or develop into sores or ulcers.

Muscle Atrophy and Weakness

This disease may cause inflammation in the muscle tissue, and some puppies will experience a decrease in muscle mass or become lethargic and weak. As muscle weakness persists, facial palsy, stiffness, and difficulty walking may also develop.

Megaesophagus

When it's dealing with dermatomyositis, your puppy might have problems swallowing due to a condition known as megaesophagus in which the organ dilates. Some dogs with megaesophagus will need to be fed sitting upright to keep food in their bodies, making this symptom difficult to manage. It can also lead to regurgitation, weight loss, or even pneumonia when food or liquid in your dog's body is aspirated.

Causes of Dermatomyositis

Dermatomyositis has been studied in both humans and dogs for decades, and it seems to be very similar in both species. This disease is not yet fully understood, but it is known that it is a hereditary condition passed from parents to puppies in their DNA:

• Genetic inheritance: While a specific cause is not known, there is a definite familial tendency for dogs to develop dermatomyositis. If one or both parent dogs have this disease, then it will likely be passed on to their offspring.
• Environmental triggers: Some dogs within certain bloodlines may be more likely to develop dermatomyositis than others. Some research suspects that vaccinations, exposure to ultraviolet (UV) light, and other environmental triggers may play a role in this auto-immune disease developing in dogs.

In dogs, dermatomyositis seems to be mainly isolated to collies and Shetland sheepdogs, but similar symptoms have been reported in other breeds. These potential breeds that may develop the disease include chow chows, Pembroke Welsh corgis, Lakeland terriers, German shepherds, Kuvasz, and any dogs mixed with these breeds.

Diagnosing Dermatomyositis in Dogs

A skin biopsy is the most commonly used method to diagnose dermatomyositis in dogs. Biopsies may also be taken from affected muscle tissue. To perform a biopsy, a sample of a skin lesion is taken and evaluated in a laboratory and examined microscopically. To obtain this biopsy, sedation or local anesthesia will most likely be utilized by your veterinarian.

Other skin diseases, including mange and ringworm, may also be ruled out by performing other tests prior to a skin biopsy. On rare occasions, a muscle biopsy and a test called an electromyogram may also be performed to diagnose dermatomyositis.

Treatment

Symptomatic treatment is heavily relied on for dogs with dermatomyositis. Medications and vitamins used to manage dermatomyositis can be expensive, and at-home care can become labor-intensive, so dog owners should prepare for a commitment to keep their pet's symptoms under control as much as possible. At-home care is especially important in patients that develop megaesophagus to ensure the dog is able to consume a healthy diet.

Pentoxifylline, vitamin E, prednisone, azathioprine, and cyclosporine are common options to manage dermatomyositis. Avoiding UV light exposure and activities that can further damage the skin are also important. Other care steps for owners may include offering assistance with feeding dogs who have difficulty swallowing and utilizing special shampoos at bath time.

Prognosis for Dogs With Dermatomyositis

There is no cure for this inherited disease, so the goal is to simply keep the dog as comfortable as possible for as long as possible. In mild cases, many dogs can recover fully as they grow older while owners manage their symptoms until they resolve. Scarring may occur on the skin of dogs with moderate cases. Unfortunately, severe dermatomyositis can cause kidney disease and inflammation of the skin and muscles that continues to progress, so this disease can be fatal. Utilizing all available treatment options can help improve the dog's condition over time to determine the severity of the disease.

How to Prevent Dermatomyositis

Since this disease is genetic, owners cannot prevent their dogs from developing it. However, responsible breeding can help breeders keep their litters from inheriting these genes. Owners with at-risk dogs may also manage their dog's lifestyle.

Selective Breeding

The best way to prevent dermatomyositis is through breeding. Selective breeding in predisposed dogs can help stop the spread of dermatomyositis through hereditary lines. A genetic test is available to test dogs for the risk level of developing dermatomyositis, but this cannot help a dog who is at high risk. Dogs who have been diagnosed with dermatomyositis, along with their first-degree relatives, should not be bred in order to lessen the likelihood of passing on these genes.

Lifestyle Management

Your dog's vaccinations should be discussed with your veterinarian (but not avoided) to determine what your specific dog needs. Exposure to UV light and extreme environmental changes should also be monitored in at-risk dogs to avoid any triggers for dermatomyositis to develop.