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Exercise intolerance and collapse

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Abstract

Exercise intolerance, which may also be considered as activity-related weakness, occurs with walking or running and dissipates with rest. It is recognized as early fatigue with mild activity, although in some cases more vigorous or prolonged exercise may be needed to induce the problem. It may be associated with episodic muscle cramps. This chapter covers clinical signs, lesion localization, pathophysiology, differential diagnosis, neurodiagnostic investigation, peripheral neuropathies, disorders of neuromuscular transmission, myopathies.

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Figures

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18.2 An approach to the work-up of animals with episodic weakness and collapse.
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18.3 Lesion localization for neuromuscular causes of collapse. Possible sites include the peripheral nerves, the neuromuscular junction (inset) and the skeletal muscles. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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18.5 Neuromuscular junction of a motor endplate. (Redrawn after deLahunta, 1983). Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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18.6 Metabolic and systemic diseases that may be responsible for weakness or collapse.
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18.7 Cardiorespiratory diseases that may be responsible for weakness or collapse.
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18.9 An overview of selected metabolic pathways in the mitochondria. ADP = adenosine diphosphate; ATP = adenosine triphosphate; CACT = carnitine translocase; CoA = coenzyme A; CoQ = coenzyme Q; CPT = carnitine palmitoyltransferase; DIC = dicarboxylate carrier; ETF = electron transfer flavoprotein; ETF-DH = electron transfer dehydrogenase; FAD = flavin adenine dinucleotide; FADH = reduced FAD; NADH = reduced nicotinamide adenine dinucleotide; PDHC = pyruvate dehydrogenase complex; TCA = tricarboxylic acid.
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18.10 Lateral radiograph demonstrating an abnormally large oesophagus (megaoesophagus) with the aid of barium contrast medium. When performing such studies, the risk of aspiration pneumonia should be considered.
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18.11 Transverse, post-contrast T1-weighted MR image of the cranial cervical spine in a dog with focal myositis, presenting with neck pain. A well defined muscle hyperintensity is visible.
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18.13 A Bailey chair used to aid in feeding dogs with megaoesophagus. (Courtesy of Roxie’s Mega Mission)
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18.14 A 9-year-old Chinese Crested dog with a pendulous abdomen and thin skin due to hyperadrenocorticism. Alopecia was obviously difficult for the owner to detect in this breed and so the condition progressed to loss of muscle mass and pelvic limb weakness.
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18.15 Muscle biopsy sample from a dog revealing the classic appearance of hypothyroid myopathy. The type I fibres are larger than the atrophied type II fibres. (Myofibrillar ATPase reaction at pH 4.3 stain; original magnification X100)
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18.16 Dystrophin–glycoprotein (DAG) complex and its relationship with the muscle membrane and contractile units. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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18.17 A fresh-frozen muscle biopsy section from a young dog with muscular dystrophy showing necrotic fibres undergoing phagocytosis, clusters of basophilic regenerating fibres (arrowed) and endomysial fibrosis. Immunohistochemistry is needed to confirm the absence of dystrophin and associated glycoproteins. (H&E stain; original magnification X100)
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18.18 A fresh-frozen muscle biopsy section from a young Great Dane with progressive muscle wasting and exercise intolerance. Note the well defined central areas within several myofibres. (NADH dehydrogenase reaction; original magnification X100)
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18.19 Modified Gomori trichrome-stained muscle biopsy specimen from a dog with suspected mitochondrial myopathy. Subsarcolemmal and intermyofibrillar deposits of membranous material stains red with the trichrome stain, and represents the accumulation of mitochondria. Myofibres with the staining pattern are called ragged-red fibres. (Original magnification X400)
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18.21 Fresh-frozen muscle section from a dog presented with exercise-related weakness and myalgia. The multiple large lipid droplets are indicative of a lipid storage myopathy. (Oil Red O stain; original magnification X400)
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18.23 A 2-year-old Miniature Schnauzer exhibiting a stiff neck posture and marked prominence of the muscles over the proximal thoracic limb and neck. The dog was diagnosed with congenital myotonia. (Courtesy of C Vite)
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18.24 A 7-month-old Labrador Retriever exhibiting profound hyperextension of the pelvic limbs due to infection of the muscles and nerve roots of the lumbar plexus. Such contractures are often permanent.
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18.26 Polymyositis in a 10-year-old Boxer with marked generalized muscle atrophy. The dog initially presented with a complaint of dysphagia due to tongue dysfunction. The flaccid dysfunctional tongue was also affected by the inflammatory process.

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Exercise-induced collapse

A Labrador Retriever with exercise-induced collapse (a) 5 minutes post-exercise

Exercise-induced collapse

(b) 10 minutes post-exercise. (Courtesy of Dr S Taylor) (See page 365 in the Manual)

Exercise intolerance

(a) Labrador Retriever with exercise intolerance due to myasthenia gravis.

Exercise intolerance

(b) A Boxer showing exercise intolerance progressing to a rigid and weak stance due to polymyositis. (See page 342 in the Manual)

Gracilis muscle myopathy

A German Shepherd Dog showing the typical gait seen with gracilis myopathy. Right rear leg. Note the shortened stride and inward rotation of leg from the hock down. (Courtesy of Dr D Lewis) (See page 366 in the Manual)

Inherited myopathy

Inherited myopathy affecting a 7-month-old Great Dane bitch, causing exercise intolerance. (Courtesy of Dr S Long and Dr J Anderson) (See page 358 in the Manual)

Muscular dystrophy

(a) A 6-month-old Springer Spaniel exhibiting the typical gait seen in muscular dystrophy associated with increased tone and decreased flexor ability in all limbs. (Courtesy of Dr E MacKillop)

Muscular dystrophy

(b) Old English Sheepdog puppy with end-stage muscular dystrophy. (See page 356 in the Manual)

Myasthenia gravis

(a) A young Border Terrier with myasthenia gravis demonstrating a profound inability to ambulate after a short burst of activity.

Myasthenia gravis

(b) The same dog, pre- and post-administration of edrophonium, which is a subjective test for myasthenia gravis. A positive response is seen following the administration of the drug. (See page 349 in the Manual)

Neuromuscular disease

A Rottweiler with diffuse neuromuscular disease, which is now so severe that there is respiratory compromise with abdominal breathing. (See page 342 in the Manual)

Steroid myopathy

A 13-year-old Dachshund demonstrating tremendous stiffness in all limbs with profound muscular atrophy. The dog had been treated with oral steroids for 3 years and had developed steroid myopathy as a consequence. (See page 353 in the Manual)

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