Because canine X-linked muscular dystrophy (CXMD) almost always is obvious at an early age, it usually can be diagnosed without much difficulty. Of course, any “sick” puppy brought to a veterinarian will have a thorough physical examination. It probably will also have a urinalysis and routine blood work, including a complete blood count and a serum biochemistry profile. The results of the chemistry profile in dogs with CXMD will show dramatically elevated levels of creatine kinase (CK). CK is an enzyme found in skeletal muscle, cardiac (heart) muscle and smooth muscle; it is also found in tissues of the brain and nerves. CK levels in circulating blood rise after muscle damage. Puppies with CXMD will have elevated CK that can be detected by as early as 1 week of age. CK levels typically plateau at about 100 x normal by 6 to 8 weeks of age.
More advanced testing to confirm the diagnosis of CXMD may not be necessary, if the dog’s clinical signs and CK levels are highly suggestive of the disease. However, several confirmatory tests are readily available to most veterinarians. Electromyography can be used to detect abnormal nerve conduction within certain muscle groups after a dog is about 10 weeks old. The attending veterinarian may recommend taking muscle biopsies for submission to a pathology laboratory. The pathologists can look at the tissue samples microscopically and evaluate them through a process known as histopathology. They can also perform a test called immunocytochemistry to look specifically for deficiencies in the levels of the important cytoskeletal protein, dystrophin. Dogs with CXMD will have very low to nonexistent levels of this protein in their muscles.
Chest films (thoracic radiographs/X-rays) may reveal megaesophagus and, if present, evidence of aspiration pneumonia. Both of these conditions frequently occur in dogs with X-linked muscular dystrophy.