Exercise intolerance in retrievers - Veterinary Medicine
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Exercise intolerance in retrievers
When a dog from one of the popular retriever breeds is brought to you because it collapsed while exercising or seems to tire easily, you need to sift through the many potential underlying causes. It could be anything from an out-of-shape weekend athlete to a dog with an inherited metabolic myopathy. Here are some of the conditions to consider.



Lack of conditioning or obesity

Some dogs presented for exercise intolerance are simply out of condition. Working dogs asked to perform without much preparatory conditioning may tire quickly and be reluctant to exercise. Dogs may not be acclimatized to extremes of heat or humidity, making it difficult to exercise without overheating.

Obesity is common in dogs, especially retrievers, and can be associated with a variety of medical disorders and orthopedic problems that can lead to exercise intolerance.3 Obese retrievers have also been shown to have small airway collapse during expiration, limiting their ability to exercise.4 Weight loss in obese dogs with hip osteoarthritis substantially improves their gait and their ability to exercise.3

Bone and joint disorders

Discomfort from abnormalities of the bones or joints causes reluctance to exercise. Lameness will not always be apparent, particularly if more than one limb is affected. Generalized stiffness and reluctance to exercise at full capacity may be the only findings in dogs with painful disorders affecting multiple bones or joints. Young dogs suffering from panosteitis, hypertrophic osteodystrophy, or osteochondritis dissecans (OCD) all show a reluctance to exercise. Older dogs with ligamentous injuries or degenerative joint disease will be similarly affected.5

Inflammatory disease affecting multiple joints, termed polyarthritis, causes joint pain and reluctance to exercise in dogs.6 Although some cases can be attributed to tick-borne infectious diseases (e.g. ehrlichiosis, Lyme disease, granulocytic anaplasmosis, bartonellosis, Rocky Mountain spotted fever), noninfectious idiopathic immune-mediated nonerosive polyarthritis (IMPA) is the most common cause of polyarthritis in dogs.6-8 Labrador retrievers and Nova Scotia duck tolling retrievers may be predisposed.6,9 In dogs with IMPA, immune complex deposition within the synovium results in a sterile synovitis. Clinical signs include reluctance to walk or exercise, fever, and lethargy. Lameness, joint swelling, and joint pain can be inconsistent, so diagnosis requires arthrocentesis with cytology and bacterial culture.6-9

Degenerative lumbosacral stenosis

The cauda equina is the collection of spinal nerve roots descending from the end of the spinal cord within the vertebral canal to their point of exit from the canal. Dogs with compression of these nerves from degenerative lumbosacral stenosis exhibit exercise intolerance and a reluctance to run or jump.10 Degenerative lumbosacral stenosis is a common disorder in aging retrievers, with cauda equina compression caused by acquired Hansen's type II disk prolapse at L7-S1, bone remodeling, and soft tissue proliferation.10 Progressive narrowing of the lumbosacral vertebral canal causes compression of the L7, sacral, and caudal nerve roots, resulting in a characteristic constellation of clinical signs.10-12 Affected dogs are slow to rise from a prone position and reluctant to run, sit up, jump, or climb stairs. Rear limb lameness and weakness commonly worsen with exercise, as the blood vessels accompanying the spinal nerve roots within the already crowded intervertebral foramen dilate, further compressing the nerve roots—a phenomenon termed neurogenic intermittent claudication.10,12,13 Some dogs will become obviously lame with exercise, while others will simply quit exercising because of the discomfort.

The most consistent physical examination abnormality in dogs with cauda equina syndrome is pain elicited by deep palpation of the dorsal sacrum, dorsiflexion of the tail, or hyperextension of the lumbosacral region.10,13 In severely affected dogs, there may also be rear limb weakness, atrophy of the muscles of the caudal thigh and distal limb, and incomplete hock flexion during the withdrawal reflex.10,12,13 Clinical findings are often the primary basis for reaching a diagnosis in affected dogs. Spinal radiographs are useful to rule out other lesions in the region such as diskospondylitis, lytic vertebral neoplasia, and vertebral fracture or luxation, and to identify predisposing factors for degenerative stenosis such as sacral osteochondrosis or vertebral malformations. When available, magnetic resonance imaging (MRI) provides the most sensitive, accurate, and noninvasive means of evaluating the lumbosacral region, allowing visualization of all components potentially involved in cauda equina compression.10-13 Restricting exercise and administering analgesics or anti-inflammatory drugs may temporarily improve the condition in some dogs with clinical signs limited to pain and lameness. More definitive treatment involves lumbosacral dorsal laminectomy, excision of compressing tissues, and L7-S1 foraminotomy when necessary.10-13


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