Page 1245 - Veterinary Immunology, 10th Edition

effectively. Dogs with transient myasthenia gravis may be
VetBooks.ir supported temporarily with long-acting anticholinesterase drugs

such as pyridostigmine bromide or neostigmine methyl sulfate.
Dogs with progressive disease that show no signs of remission may

benefit from immunosuppression. Positive clinical responses have
been reported in dogs treated with prednisone or azathioprine or
both. However, corticosteroid treatment may result in transient
exacerbation of symptoms. Plasmapheresis has been used for short-

term therapy to stabilize patients before thymectomy.

Polymyositis

A generalized autoimmune myositis occurs in large dogs such as
German Shepherds, Boxers, and Retrievers. Hungarian Vizslas

suffer from a breed-specific inflammatory myopathy. In all these
cases, the animals show progressive muscle weakness not
associated with exercise intolerance. Changes in laryngeal muscle

function lead to a change in the voice. Megaesophagus may lead to
dysphagia and if severe can result in aspiration pneumonia.
Affected animals may develop a shifting lameness. Animals may be
febrile and develop leukocytosis and eosinophilia. Biopsies show
muscle fiber degeneration, necrosis, and vacuolation, and affected

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muscles may be infiltrated by CD8 lymphocytes and plasma cells.
About 50% of affected dogs have antinuclear antibodies or
antibodies to sarcolemma, or both. Corticosteroids are the treatment

of choice.
A similar immune-mediated myositis has been recorded in
Quarter Horses and related breeds. It causes rapid atrophy of the
gluteal and epaxial muscles. The affected muscles are infiltrated
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with macrophages and CD4 T cells with lesser numbers of CD8 T
cells and B cells. It too may be treatable with corticosteroids. MHC
class I and II are expressed on the sarcolemma of some myofibers of
affected horses but not in normal horses.

Autoimmune Masticatory Myositis

Dogs may develop a focal myositis confined to the muscles of
mastication. The major autoantigen is masticatory myosin-binding

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