Not shown were absent patellar reflexes and reduced withdrawal reflexes. When the dog walked normal after a period of rest the neurologic examination was normal including patellar reflexes. The physical and orthopedic examinations were normal.
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Dog - Labrador Retriever
Exercise intolerance
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L4 to L6 spinal cord segments/ventral grey column cell bodies, spinal roots, spinal nerves; femoral nerves, neuromuscular junctions; quadriceps femoris muscles.
Note the appearance of lameness in the gait with shortened strides. This can be from discomfort or lack of support or both. Note the absence of any obvious ataxia.
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Ischemic neuromyopathy secondary to a caudal aortic thrombosis is a recognized cause of intermittent claudication but is a rare disorder in dogs. Femoral artery pulses should be diminished or absent during the fatigue and in comparison to the thoracic limb paws, the pelvic limb paws should feel cool. Exercise induced collapse is a disorder of young adult Labrador Retrievers. However, all four limbs are affected; there is no evidence of discomfort; and they vigorously struggle to remain standing and to keep moving. Patellar reflexes are absent during the fatigue.
Myasthenia gravis is a common cause of exercise intolerance in dogs. The sole involvement of the pelvic limbs and the asymmetry would be unusual. Reflex loss is not seen in dogs still able to walk. Iliopsoas injury with femoral neuropathy should not be intermittent and the affected dog usually exhibits extreme discomfort, especially with manipulation (medial rotation combined with abduction) at the coxofemoral joint.
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Serum antibodies for muscle acetylcholine receptors were not present. CK level at the referring veterinary hospital was normal. CK level determined by the veterinary neurologist was 1010 U/I. A repeat study of the CK level both pre and post exercise was normal.
Abdominal aorta ultrasound examination revealed a 9cm thrombus located just cranial to the termination of the abdominal aorta. A development of an associated extensive collateral circulation was observed. In the cat, experimental ligation of this region of the abdominal aorta does not result in neurologic signs. Preexisting experimental collateral circulation from the 5th, 6th and 7th lumbar arteries via epaxial muscle arteries results in pelvic limb blood supply. The formation of the thrombus is thought to inhibit the development of this collateral circulation through a humoral effect.
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Caudal aortic thrombosis with secondary ischemic neuromyopathy
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Using fluoroscopic guidance, vascular stents were tunneled into the thrombus via a femoral artery and carotid artery. The stents were expanded to open the lumen, compressing the thrombus circumferentially into the aortic wall. The dog was treated with long-term anticoagulant medication. Misty returned to normal shortly after the procedure, and follow up imaging demonstrated unimpeded blood flow through the area.
We thank Dr. Dharshan Neravanda from Dogs and Cats Veterinary Referral in Bowie, Maryland for the use of this case study and images.
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