Metabolic Myopathy in Dogs

This disorder of muscle fibers results because of the interference of chemical reactions involved in drawing energy from the food that your dog consumes. Because the energy levels are low, the muscles become weak. In addition, unused fuel molecules are building up inside the muscles, causing damage. Any sign of general weakness, or fatigue with exercise should be discussed with your pet’s veterinarian.

A metabolic muscle disease interferes with the reaction of the body’s metabolism (chemical changes that take place within the cells). This defect affects all voluntary muscles. Classified as non-inflammatory, a metabolic muscle disease is also called a metabolic myopathy.

Metabolic muscle disease can have a large impact on your dog’s day to day life. The effect will vary, depending on the type of disease; symptoms could be as listed below.

• General weakness
• Exercise intolerance
• Muscle pain
• Limited joint movement
• Regurgitation
• Limited esophageal movement (megaesophagus)
• Spasm of jaw muscles (trismus)
• Ventroflexion of head and neck
• Local or general muscle atrophy (decrease in muscle mass)
• Hypertrophy (increase in muscle mass due to increase in cell size)
• Stunted growth
• Lameness
• Stiff and stilted gait
• Body and limb tremors
• Swelling
• Dark urine

Types

Metabolic myopathies can affect your pet’s mobility and desire to participate in his usual activities. A small sample of the types of illness that can contribute are found here.

• Type II Muscle Fiber Deficiency
• This results from a deficiency in the form or function of the muscle fiber
• This is a congenital illness
• The condition starts when the dog is just a pup, and can stabilize around 6 to 12 months of age
• Labrador Retrievers (both black and yellow) can be prone
• Fibrotic Myopathy
• This is a degeneration of the thigh muscle
• There is an abnormal tightening of the muscle
• The tissues become thick
• German Shepherd are predisposed
• Exertional Myopathy (Rhabdomyolysis)
• The disease is caused by inadequate blood supply to the muscle after exercise or excitement
• The muscle cells are damaged
• Greyhounds, sled dogs, hunting dogs and trial competition dogs are affected most often
• Great Dane Myopathy
• There is autosomal recessive inheritance causing this condition
• Increased creatinine activity is evident upon testing
• Supportive treatment is the only option thus far

Not all of the causes of the numerous metabolic muscle diseases have been pinpointed. There are several causes suspected to date.

• Genetics
• Idiopathic (unknown)
• Nutritional imbalance
• Inadequate supply of blood to the muscle during exercise
• Biochemical defect in energy processing
• Ingestion of poison
• Injury
• Overuse of muscle

Once you have made the appointment for your pet’s veterinary visit, take some time before going to the veterinarian to document your dog’s behaviors. Track his physical activity and exercise tolerance. If you see notable changes that you feel would be beneficial for the veterinarian to know, write them down as a written reference for the veterinary team. When we are with our beloved family pet in the examination room, it is often difficult to remember exactly the details and discussion we had planned to relay.

Your veterinarian will begin with a physical examination which will include a manipulation of your dog’s limbs to determine the joint function, the range of motion, pain tolerance, and muscle mass.

The veterinary team will analyse the urine (myoglobin in the urine is associated with rhabdomyolysis, for example), and do diagnostic blood tests to check for important markers such as serum creatinine, serum electrolytes, blood plasma and blood lactate.

Thoracic and limb radiographs may be suggested. Electromyography, to assess the health of the muscles and nerves, can prove very useful. Sometimes a thyroid screen is needed, depending on the symptoms your dog is exhibiting. DNA testing is also available as a tool for determining the presence of some metabolic muscle disorders.

A biopsy, and subsequent histopathology (the study of tissues under the microscope) can verify the condition of the muscle and any damage that might have occurred with the progression of the disease.

Extensive studies have been undertaken to further understand and treat metabolic myopathies. To date, most of these conditions offer supportive care only, in the form of rest, nutrition and supplementation (for instance, I-carnitine is an amino acid prescribed to aid in protein building).

At best, for fibrotic myopathy, surgery can be an option, keeping in mind that recurrence is very possible. Exertional myopathy is treated with a fluid injection, body cooling, muscle relaxants, and rest, but muscle loss can occur with episodes and recovery can be slow.

Due to the nature of this condition, the reality of the lifelong exercise restrictions should be faced head on. You must recognize that advanced stages of the disease will result in a pet who has limited mobility for life. Because some of the conditions under the umbrella of metabolic muscle disease can result in serious muscle damage with concurrent episodes, it is recommended that you do not encourage over exertion in the form of extreme running or competition. Long walks are still a possibility that you can enjoy with your canine companion, but take care to keep him well hydrated and do not expose him to high temperatures. Offer him plenty of rests in the shade as you enjoy the outdoors.

Metabolic muscle disease will progress; only in the case of an illness like Type II muscle fiber deficiency does it have a chance of stabilising. Keep in communication with your veterinarian, and along with her help, you will be able to offer a good quality of life for your pet.