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Muscles Inflammatory - Pathology (view source)

Revision as of 20:15, 18 August 2008

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==Myositis==
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*Inflammation of muscle
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===Bacterial myositis===
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*Bacteria gain entry via:
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**Direct penetration
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**Blood stream
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**Extension
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*Lesions caused:
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**Suppurative
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**Serosanguinous
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**Granulomatous
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====Abscesses====
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*Caused by pyogenic bacteria
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*Usually:
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**[[Arcanobacter pyogenes|''Arcanobacterium pyogenes'']] in sheep and cattle
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**[[Respiratory Bacterial Infections - Pathology#Strangles|''Streptococcus equi'']] in horses
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**[[Corynebacterium species|''Corynebacterium pseudotuberculosis'']] in sheep and goats
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**[[Pasteurella species and Mannheimia haemolytica|''Pasteurella multocida'']] causes cellulitis in cats
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*Usually localised suppuration and necrosis of myofibres
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*Occasionally my spread via the fascia
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====Black leg====
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[[Image:Black leg myositis.jpg|right|thumb|100px|<small><center>Blackleg myositis (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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*Causative agent: [[Clostridium species|''Clostridium chauvoei'']]
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*May affect the fattest cattle at pasture in the summer
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*Rapid toxaemia -> death
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*If clinical signs observed:
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**Toxaemia -> pyrexia, depression, [[Lungs Circulatory - Pathology#Pulmonary oedema|pulmonary oedema]], circulatory collapse
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**Muscle lesions -> lameness, swollen hot muscles later becoming cool as necrosis sets in
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*Pathogenesis:
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**Spores gain entry to GI tract -> blood -> muscle -> lie latent
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**Under right conditions (usually anaerobic following injury) they germinate and bacilli grow
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**Toxin damages capillaries -> serosanguinous exudate
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**Muscle necrosis due to gas producing bacteria -> emphysaema and crepitus
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*Grossly:
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**Early stages
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***At muscle periphery
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***Dark red
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***Distended by serous or serosanguinous exudate
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***Wet cut surface
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**Old stages
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***Centre of lesion is full of gas bubbles, porous, dry, reddish black
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***Rancid odour
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*Histologically:
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**Early stages
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***Separation of myofibres by exudate
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***[[General Pathology - Necrosis#Coagulation Necrosis|Coagulative necrosis]]
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***No nuclei
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**Old stage
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***Fragmented muscle fibres separated by gas bubbles
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***Gram positive bacilli may be found in clumps
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====[[General Pathology - Necrosis#Gas Gangrene|Gas gangrene]]====
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*Causative agents: [[Clostridium species|''Clostridium septicum, C. novyi, C. perfringens, C. sordelli'']]
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*Normally in soil
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*Bacteria gain entry as spores via penetrating wounds
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*Serohaemorrhagic myositis
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*If only subcutis and fascia are involved - '''malignant oedema'''
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*Toxaemia and septicaemia -> rapid death
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====[[Oral Cavity - Tongue#Actinobacillosis|Wooden tongue]]====
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*Also called '''Actinobacillosis'''
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*Caused by [[Actinobacillus species|''Actinobacillus lignieresii'']]
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*Usually due to direct penetration into [[Oral Cavity - Tongue - Anatomy & Physiology|tongue]] of cattle
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*Small granulomatous lesions containing 'sulfa granules' of large numbers of gram-negative rods
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====Tuberculosis====
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*Caused by [[Mycobacteria spp.|''Mycobacterium bovis'']]
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*Grossly:
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**Yellowish spherical nodules
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**[[General Pathology - Necrosis#Caseation Necrosis|Caseous content]]
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**Fibrous capsule usually
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*Histologically:
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**Granuloma
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**Central necrosis
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**Epitheliod and giant cells at periphery
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====[[Actinomycetes|''Actinomycosis bovis'']]====
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*May extend to muscles, especially masseters, from [[Bones Inflammatory - Pathology#Osteomyelitis|osteomyelitis]]
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*Histologically:
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**Caseous or suppurative centres of lesions
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**Epithelioid and giant cells at periphery
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**'Sulfa granules' at centre - gram-positive branching rods
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====Botryomycosis====
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*Caused by [[Staphylococcus spp.|''Staphylococcus aureus'']]
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*Occurs in horses and pigs usually due to wounds
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*Lowgrade persistent infection -> granulomatous lesions
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*Grossly:
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**Hard nodules with fibrous capsule in muscles
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**Contain yellow-brown pus and granules
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*Histologically:
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**Encapsulated granulomatous lesions
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**Central club colonies
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**Staphylococci are present
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===Viral myositis===
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*Rare in the UK
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====Porcine encephalomyelitis====
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*Caused by [[Coronaviridae|Coronavirus]]
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*May cause multifocal myofibre necrosis + focal interstitial and perivascular lymphocyte, macrophage and neutrophil infiltration
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====Foot and Mouth disease====
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*Caused by [[Picornaviridae|Apthovirus]]
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*Main presentation are vesicles
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*May also involve skeletal and heart muscle
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*Grossly:
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**Yellow streaks and grey foci
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*Histologically:
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**Segmental myofibre [[Muscles Degenerative - Pathology#Necrosis|necrosis]]
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**Infiltration of lymphocytes and neutrophils
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====Bluetongue====
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*Caused by [[Reoviridae|bluetongue virus of family Reoviridae]]
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*Non-contagious
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*Insect-borne
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*Causes vasculitis, especially in oral cavity
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*Grossly:
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**Infarctions -> necrosis
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**Haemorrhage
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*Histologically:
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**Necrosis -> calcification or regeneration (depends on age of lesion)
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===Parasitic myositis===
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[[Image:taenia ovis cysticerci.jpg|right|thumb|100px|<small><center>''T. ovis'' cysticerci (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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[[Image:Sarcocyst in muscle.jpg|right|thumb|100px|<small><center>Sarcocyst (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
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*Rare in domestic animals
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====Nematodes====
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*[[Trichinelloidea|'''''Trichinella''''']] larvae
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**Particularly in pigs and dogs
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**Public health and economic importance
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**''T. spiralis'' affecting dogs, pigs, cats and humans is most common in hotter climates
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**Larvae distend myofibres
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**May be seen grossly if dead and calcified
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**Predilection for active muscles, ''e.g.'' diaphragm, intercostal, masseter and tongue muscles
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**Histologically:
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***Focal myositis - neutrophils, lymphocytes, eosinophils
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*[[Ancylostomatoidea|''Ancylostoma'']] larvae
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**Cause inflammation and [[Muscles Degenerative - Pathology#Necrosis|necrosis]]
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*[[Ascaridoidea|Ascarid]] larvae
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*[[Dirofilaria immitis|''Dirofilaria immitis'']] in dogs causing ischaemic myopathy due to [[Muscles Degenerative - Pathology#Ischaemia|infartcs]]
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====Cestodes====
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*[[Taenia|''Taenia solium, '']] - cysticercosis in swine and humans
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*[[Taenia|''T. ovis'']] - cysticercosis in sheep
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*[[Taenia|''T. saginata'']] in cattle cysticercosis
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*[[Taenia|''Multiceps serialis'']] in rabbits, primates coenurosis
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*[[Echinococcus|''Echinococcus granulosus'']] hydatid disease in herbivores and humans
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====Protozoa====
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*[[Tissue cyst-forming coccidia|'''''Toxoplasma gondii''''']]
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**Cats as final hosts
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**Intermediate hosts, birds and mammals have tachyzoites throughout body, infrequently in skeletal muscle
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**Histologically:
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***Multifocal [[Muscles Degenerative - Pathology#Necrosis|necrosis]] of myofibres
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***Lymphocyte and plasma cell infiltration
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***In later stages bradyzoite cysts
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*[[Tissue cyst-forming coccidia|'''''Neospora caninum''''']]
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**Necrotising inflammation of muscles
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**Myositis more severe than in toxoplasmosis
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*[[Tissue cyst-forming coccidia|'''''Sarcocystis''''']]
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**Histologically:
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***Merozoites causing focal and segmental [[Muscles Degenerative - Pathology#Necrosis|necrosis]]
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***May involve [[Muscles Degenerative - Pathology#Calcification|mineralisation]]
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***Non-purulent myositis with plasma cells, lymphocytes and macrophages
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**Diaphragm and masseters most severely affected
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*[[Bones Hyperplastic and Neoplastic - Pathology#Hepatozoon|'''''Hepatozoon americanum''''']]
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**Develop cysts in skeletal muscle of dogs and cats
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**May be accompanied by pyogranulomatous myositis - macrophages and neutrophils mainly with occasional other cells
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*'''''Trypanosoma'''''
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**Infrequent muscle lesions with mononuclear infiltrates
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**Dogs, cats and pigs are affected
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**Parasites lie between myofilaments
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**May cause fibre degeneration
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*'''''Babesia bovis'''''
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**In cattle
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**Infrequent muscle [[Muscles Degenerative - Pathology#Necrosis|necrosis]]
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====Arthropods====
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*Dipterious larvae causing myiasis
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*[[Insecta|''Hypoderma'' spp.]] in cattle
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**May occasionally burrow into muscle
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===Immune-mediated myositis===
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====Masticatory muscle myositis (MMM)====
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*Occurs in dogs
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*Tends to affect the masseter and temporalis muscles
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*Autoantibodies selectively attack muscles of mastication (type IIM fibres)
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*Acute stage = eosinophilic myositis
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**Extremely swollen, painful, hard masticatory muscles
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*Chronic stage = atrophic myositis
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**Atrophy may occur without previous acute stage
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*Grossly:
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**Bilateral but not necessarily symmetrical
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**At first, enlarged and oedematous muscles becominf dark red, firm with reddish streaks and yellowiss foci
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*Histologically:
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**Acute lesions:
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***Mainly eosinophilic infiltrate, few lymphocytes, monocytes and plasma cells
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***In recurrent disease plasma cells predominate
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***[[Muscles Degenerative - Pathology#Necrosis|Necrotic]] myofibres, [[Muscles Degenerative - Pathology#Atrophy|atrophy]] and attempted [[Muscles - normal#Regeneration|regeneration]]
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**Chronic stage:
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***[[Muscles Degenerative - Pathology#Atrophy|Atrophy]] predominates
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***Fasciculi are shrunken
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***Condensation of stroma -> enlarged endomysium
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***Focal plasma cell and lymphocyte infiltration
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====[[Muscles Developmental - Pathology#Canine dermatomyositis|Canine dermatomyositis]]====
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===Idiopathic myositis===
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====Canine polymyositis====
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*DOES NOT include MMM above
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*Rare
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*Clinical signs:
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**Muscle pain
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**Fever
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**Weakness, particularly in hind limbs
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*Grossly:
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**Inflammation is accompanied by muscle necrosis and regeneration
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*Histologically:
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**Inflammatory foci with lymphocytes, plasma cells and occasionally eosinophils
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*Possibly immunological cause
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*Single biopsy may not be enough to make the diagnosis as it tends to be multifocal and disseminated
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*Lesions similar to some infectious causes (such as [[Tissue cyst-forming coccidia|''Toxoplasma gondii'']])
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====Canine bilateral extraocular polymyositis====
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*In Golden retrievers
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*Very rare
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*Clinical signs:
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**Acute bilateral exophthalmos
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*Involves only extraocular muscles except for retractor blbi
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*Grossly:
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**Swollen and pale extraocular muscles
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*Histologically:
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**Sterile myositis
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**Multifocal necrosis of myofibres
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**Lymphocytic, histiocytic and plasmacytic infiltrate with few neutrophils
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====Bovine and ovine eosinophilic myositis====
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*Unknown aetiology
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*Major cell involved is eosinphil
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*Usually noticed at slaughter - green muscle discoloration
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*May be caused by degenteration of [[Tissue cyst-forming coccidia|''Sarcocystis'' spp.]]
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*Grossly:
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**Green discolored areas, well demarcated
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**Mostly in muscles of back and thighs
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*Histologically:
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**Massive eosinophil infiltration
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**Muscle fibres may degenerate
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**In old lesions - endimysial fibrosis, myofibre atrophy, some regeneration, lymphocytes, plasma cells, macrophages and few eosinophils
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**Capsule may form
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