The muscles of most aged mammals lose much of their strength and actually decrease in size with each advancing year. This is a normal part of the aging process and is to be expected. However, there are two as yet poorly understood muscle disorders which at first may look like normal aging weakness.
In one the dog develops weakness in the leg muscles during periods of exercise or other physical stress, may fall down briefly, seem to recover, get up for a short time only to fall down again. This is often seen in polymyositis, a disease which causes inflammation of any or all muscles in the body.
Polymyositis occurs mostly in late middle age and early old age, the most common of its several possible causes appearing to be a defect in the dog’s immune mechanism. Treatment with corticosteroids is quite successful despite the often alarming appearance of the dog. Occasionally the muscles of the esophagus are affected, making swallowing difficult, but even these respond.
Muscular dystrophy, the second disorder, occurs mainly in older dogs, bears some similarity to muscular dystrophy in people, and has a cause as yet unknown. Affected dogs develop a stiff gait as the muscles become progressively weaker and smaller in size. There is nothing we know of which will stop the deterioration or cure the disease. Treatment is palliative, trying to keep the patient as comfortable as possible, and is based on your dog’s individual symptoms.