Myopathy is a term referring to any of a number of diseases that affect the muscles and nerves in dogs as well as humans, cats and many other animals. Canines can exhibit one type of myopathy due to a single cause, or they may suffer from a variety of myopathies and therefore have polymyopathy. Because polymyopathy has many of the same symptoms as any single myopathic disorder, it can be difficult to diagnose.
Dogs with polymyopathy exhibit symptoms such as pain after exercise, reluctance to move, generalized weakness, muscle unresponsiveness and awkward gait. Symptoms vary from animal to animal. In some, muscle pain may come and go, while in others, muscle weakness may be a response to exercise as opposed to consistently present. For the most part, dogs with polymyopathy do not move much, and exhibit attacks of weakness. Although these symptoms all sound like they should affect an old dog, many types of myopathy are apparent shortly after birth.
Myopathies are often genetically inherited conditions, such as in the case of canine muscle myopathy or centronuclear myopathy, which often affects Labradors. Inflammatory myopathy is another type, and isn’t necessarily hereditary, as it can also be caused by parasitic infections. It appears between 3 months and 14 years after birth, according to the Journal of Veterinary Internal Medicine. Lipid storage myopathy causes dogs to accumulate fat in their muscles. Several peripheral neuropathies, which affect nerves instead of muscles, also cause the same symptoms as muscular myopathies.
Because of the variety of myopathies and because many of them share symptoms with neurological disorders, it is difficult for vets to pin down specific diagnoses. To do so they use tissue samples such as muscle and nerve biopsies, blood analysis and tests of dogs’ endocrine systems, which regulates hormones. They can also take samples of various substances dogs generate before and after exercise to help make a correct diagnosis.
Unfortunately, dogs with genetically inherited myopathies don’t have much hope and usually need to be put to sleep. However, dogs with problems in their endocrine systems or primary illnesses -- such as those caused by ticks -- have a chance at recovering if the initial disorder is treated. Animals with unregulated hormones often also recover once the hormone disorders are treated. Vets often treat metabolic myopathies such as lipid storage myopathy with daily vitamin regimens to successfully clear up symptoms.