Muscle Wasting in Dogs

By Maureen Malone

Muscle wasting is often a sign of another illness requiring veterinary diagnosis and treatment. Some common causes of muscle wasting in dogs include myositis, degenerative myelopathy, hypothyroidism and some tick-borne diseases.

Degenerative Myelopathy

Degenerative myelopathy is a condition in which a dog's spinal cord degenerates over time. In addition to muscle loss, symptoms include swaying in the hindquarters when standing, easily falling over when pushed from the side, difficulty getting up and dragging the hind feet when walking. As the disease progresses, dogs may become paralyzed and lose bladder and bowel control.

The disease is most common in German shepherds, Siberian huskies and collies between the ages of 4 and 14. Degenerative myelopathy is diagnosed by ruling out other conditions that may be causing the symptoms such as arthritis and hip dysplasia. Diagnostic testing might include X-rays and other diagnostic imaging, tissue biopsies and cerebrospinal fluid analysis. The cause of degenerative myelopathy is unknown and there is no effective treatment.

Underactive Thyroid

Hypothyroidism, or an underactive thyroid, in dogs causes muscle loss, weight gain, hair loss, dull fur and flaky skin. It is most commonly seen in breeds such as golden retrievers, Irish setters and dachshunds between the ages of 4 and 10. The condition is easily diagnosed with a blood test and is treated with an oral medication called levothyroxine or L-thyroxine.

Masticatory and Generalized Myositis

Myositis is a muscle disease that initially causes swelling in the muscle and later results in muscle wasting. Specific symptoms vary depending on which muscles are affected. Masticatory myositis affects the muscles that dogs use to chew, making it difficult for them to eat or drink. As the disease progresses, the muscles eventually lock, making your dog unable to open his mouth.

Polymyositis, or generalized myositis, affects multiple muscles in the dog's body. Symptoms may include muscle pain, a stiff gate, vomiting and difficulty swallowing.

Polymyositis is diagnosed with a muscle tissue sample to check for inflammation. Masticatory myositis is diagnosed with a blood test for antibodies against the masticatory muscles. Additional testing may be necessary to determine underlying causes such as a viral or bacterial infection or cancer.

Myositis usually is treated with high doses of steroids to suppress the immune system attack on the muscles. Other immunosuppresive medications such as azathioprine or cytarabine also may be used. In rare cases, dogs may be weaned off of these medications. However, in most cases, they will be on low doses of steroids for the rest of their lives.

Tick-Borne Diseases

The tick-borne disease, Hepatozoonosis, causes muscle wasting, fever, pain and eye discharge. Diagnosis is confirmed using a muscle biopsy. There is no cure for the disease, but treatment can help extend the dog's life span and quality of life. Treatment options include anti-parasitic and anti-inflamatory medication for acute infections. The medication Decoquinate helps to prevent a relapse of the disease. Without treatment, hepatozoonosis is usually fatal within months.

Hepatozoonosis is carried by some ticks and is common in the southern part of the United States. Unlike other tick diseases, such as Lyme disease or Rocky Mountain spotted fever, ticks don't transmit the disease through a bite. Rather, dogs are infected when they ingest an infected tick.