CONDITIONS ASSOCIATED WITH EXERCISE INTOLERANCE
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
|
Featuring Information from:
