View source for Muscles Inflammatory - Pathology

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==Myositis==

*Inflammation of muscle


===Bacterial myositis===

*Bacteria gain entry via:
**Direct penetration
**Blood stream 
**Extension 
*Lesions caused:
**Suppurative
**Serosanguinous
**Granulomatous


====Abscesses====

*Caused by pyogenic bacteria
*Usually:
**[[Arcanobacter pyogenes|''Arcanobacterium pyogenes'']] in sheep and cattle
**[[Respiratory Bacterial Infections - Pathology#Strangles|''Streptococcus equi'']] in horses
**[[Corynebacterium species|''Corynebacterium pseudotuberculosis'']] in sheep and goats
**[[Pasteurella species and Mannheimia haemolytica|''Pasteurella multocida'']] causes cellulitis in cats
*Usually localised suppuration and necrosis of myofibres
*Occasionally my spread via the fascia


====Black leg====
[[Image:Black leg myositis.jpg|right|thumb|100px|<small><center>Blackleg myositis (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]

*Causative agent: [[Clostridium species|''Clostridium chauvoei'']]
*May affect the fattest cattle at pasture in the summer
*Rapid toxaemia -> death
*If clinical signs observed:
**Toxaemia -> pyrexia, depression, [[Lungs Circulatory - Pathology#Pulmonary oedema|pulmonary oedema]], circulatory collapse
**Muscle lesions -> lameness, swollen hot muscles later becoming cool as necrosis sets in
*Pathogenesis:
**Spores gain entry to GI tract -> blood -> muscle -> lie latent 
**Under right conditions (usually anaerobic following injury) they germinate and bacilli grow
**Toxin damages capillaries -> serosanguinous exudate
**Muscle necrosis due to gas producing bacteria -> emphysaema and crepitus
*Grossly:
**Early stages
***At muscle periphery
***Dark red
***Distended by serous or serosanguinous exudate
***Wet cut surface
**Old stages
***Centre of lesion is full of gas bubbles, porous, dry, reddish black
***Rancid odour
*Histologically:
**Early stages
***Separation of myofibres by exudate
***[[Necrosis - Pathology#Coagulation Necrosis|Coagulative necrosis]]
***No nuclei
**Old stage
***Fragmented muscle fibres separated by gas bubbles
***Gram positive bacilli may be found in clumps


====[[Necrosis - Pathology#Gas Gangrene|Gas gangrene]]====

*Causative agents: [[Clostridium species|''Clostridium septicum, C. novyi, C. perfringens, C. sordelli'']]
*Normally in soil
*Bacteria gain entry as spores via penetrating wounds
*Serohaemorrhagic myositis
*If only subcutis and fascia are involved - '''malignant oedema'''
*Toxaemia and septicaemia -> rapid death


====[[Tongue - Pathology#Actinobacillosis|Wooden tongue]]====

*Also called '''Actinobacillosis'''
*Caused by ''[[Actinobacillus lignieresii]]''
*Usually due to direct penetration into tongue of cattle
*Small granulomatous lesions containing 'sulfa granules' of large numbers of gram-negative rods

====Tuberculosis====

*Caused by [[Mycobacteria spp.|''Mycobacterium bovis'']]
*Grossly:
**Yellowish spherical nodules
**[[Necrosis - Pathology#Caseation Necrosis|Caseous content]]
**Fibrous capsule usually
*Histologically:
**Granuloma
**Central necrosis
**Epitheliod and giant cells at periphery


====[[Actinomycetes|''Actinomycosis bovis'']]====
*"Lumpy jaw"
*May extend to muscles, especially masseters, from [[Bones Inflammatory - Pathology#Osteomyelitis|osteomyelitis]]
*Histologically:
**Caseous or suppurative centres of lesions
**Epithelioid and giant cells at periphery
**'Sulfa granules' at centre - gram-positive branching rods

====Botryomycosis====

*Caused by [[Staphylococcus spp.|''Staphylococcus aureus'']]
*Occurs in horses and pigs usually due to wounds
*Lowgrade persistent infection -> granulomatous lesions
*Grossly:
**Hard nodules with fibrous capsule in muscles
**Contain yellow-brown pus and granules
*Histologically:
**Encapsulated granulomatous lesions
**Central club colonies
**Staphylococci are present


===Viral myositis===

*Rare in the UK

====Porcine encephalomyelitis====

*Caused by [[Coronaviridae|Coronavirus]]
*May cause multifocal myofibre necrosis + focal interstitial and perivascular lymphocyte, macrophage and neutrophil infiltration


====Foot and Mouth disease====

*Caused by [[Picornaviridae|Apthovirus]]
*Main presentation are vesicles
*May also involve skeletal and heart muscle
*Grossly:
**Yellow streaks and grey foci
*Histologically:
**Segmental myofibre [[Muscles Degenerative - Pathology#Necrosis|necrosis]]
**Infiltration of lymphocytes and [[Neutrophils - WikiBlood|neutrophils]]


====Bluetongue====

*Caused by [[Reoviridae|bluetongue virus of family Reoviridae]]
*Non-contagious
*Insect-borne
*Causes vasculitis, especially in oral cavity
*Grossly:
**Infarctions -> necrosis
**Haemorrhage
*Histologically:
**Necrosis -> calcification or regeneration (depends on age of lesion)


===Parasitic myositis===
[[Image:taenia ovis cysticerci.jpg|right|thumb|100px|<small><center>''T. ovis'' cysticerci (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
[[Image:Sarcocyst in muscle.jpg|right|thumb|100px|<small><center>Sarcocyst (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
*Rare in domestic animals


====Nematodes====

*[[Trichinelloidea|'''''Trichinella''''']] larvae
**Particularly in pigs and dogs
**Public health and economic importance
**''T. spiralis'' affecting dogs, pigs, cats and humans is most common in hotter climates
**Larvae distend myofibres
**May be seen grossly if dead and calcified
**Predilection for active muscles, ''e.g.'' diaphragm, intercostal, masseter and tongue muscles
**Histologically:
***Focal myositis - [[Neutrophils - WikiBlood|neutrophils]], lymphocytes, eosinophils

*[[Ancylostomatoidea|''Ancylostoma'']] larvae
**Cause inflammation and [[Muscles Degenerative - Pathology#Necrosis|necrosis]]
*[[Ascaridoidea|Ascarid]] larvae
*[[Dirofilaria immitis|''Dirofilaria immitis'']] in dogs causing ischaemic myopathy due to [[Muscles Degenerative - Pathology#Ischaemia|infartcs]]


====Cestodes====

*[[Taenia|''Taenia solium, '']] - cysticercosis in swine and humans
*[[Taenia|''T. ovis'']] - cysticercosis in sheep
*[[Taenia|''T. saginata'']] in cattle cysticercosis
*[[Taenia|''Multiceps serialis'']] in rabbits, primates coenurosis
*[[Echinococcus|''Echinococcus granulosus'']] hydatid disease in herbivores and humans

====Protozoa====

*[[Toxoplasma|'''''Toxoplasma gondii''''']]
**Cats as final hosts
**Intermediate hosts, birds and mammals have tachyzoites throughout body, infrequently in skeletal muscle
**Histologically:
***Multifocal [[Muscles Degenerative - Pathology#Necrosis|necrosis]] of myofibres
***Lymphocyte and plasma cell infiltration
***In later stages bradyzoite cysts
*[[Neospora|'''''Neospora caninum''''']]
**Necrotising inflammation of muscles
**Myositis more severe than in toxoplasmosis
*[[Sarcocystis|'''''Sarcocystis''''']]
**Histologically:
***Merozoites causing focal and segmental [[Muscles Degenerative - Pathology#Necrosis|necrosis]]
***May involve [[Muscles Degenerative - Pathology#Calcification|mineralisation]]
***Non-purulent myositis with plasma cells, lymphocytes and macrophages
**Diaphragm and masseters most severely affected
*[[Bones Hyperplastic and Neoplastic - Pathology#Hepatozoon|'''''Hepatozoon americanum''''']]
**Develop cysts in skeletal muscle of dogs and cats
**May be accompanied by pyogranulomatous myositis - macrophages and [[Neutrophils - WikiBlood|neutrophils]] mainly with occasional other cells 
*'''''Trypanosoma'''''
**Infrequent muscle lesions with mononuclear infiltrates
**Dogs, cats and pigs are affected
**Parasites lie between myofilaments
**May cause fibre degeneration
*'''''Babesia bovis'''''
**In cattle
**Infrequent muscle [[Muscles Degenerative - Pathology#Necrosis|necrosis]]


====Arthropods====

*Dipterious larvae causing myiasis
*[[Insecta|''Hypoderma'' spp.]] in cattle
**May occasionally burrow into muscle


===Immune-mediated myositis===

====Masticatory muscle myositis (MMM)====

*Occurs in dogs
*Tends to affect the masseter and temporalis muscles
*Autoantibodies selectively attack muscles of mastication (type IIM fibres)
*Acute stage = eosinophilic myositis
**Extremely swollen, painful, hard masticatory muscles
*Chronic stage = atrophic myositis
**Atrophy may occur without previous acute stage
*Grossly:
**Bilateral but not necessarily symmetrical
**At first, enlarged and oedematous muscles becominf dark red, firm with reddish streaks and yellowiss foci
*Histologically:
**Acute lesions:
***Mainly eosinophilic infiltrate, few lymphocytes, [[Monocytes - WikiBlood|monocytes]] and plasma cells
***In recurrent disease plasma cells predominate
***[[Muscles Degenerative - Pathology#Necrosis|Necrotic]] myofibres, [[Muscles Degenerative - Pathology#Atrophy|atrophy]] and attempted [[Muscle Regeneration - Anatomy & Physiology|regeneration]]
**Chronic stage:
***[[Muscles Degenerative - Pathology#Atrophy|Atrophy]] predominates
***Fasciculi are shrunken
***Condensation of stroma -> enlarged endomysium
***Focal plasma cell and lymphocyte infiltration

====[[Muscles Developmental - Pathology#Canine dermatomyositis|Canine dermatomyositis]]====


===Idiopathic myositis===

====Canine polymyositis====	

*DOES NOT include MMM above
*Rare
*Clinical signs:
**Muscle pain
**Fever
**Weakness, particularly in hind limbs
*Grossly:
**Inflammation is accompanied by muscle necrosis and regeneration
*Histologically:
**Inflammatory foci with lymphocytes, plasma cells and occasionally eosinophils
*Possibly immunological cause
*Single biopsy may not be enough to make the diagnosis as it tends to be multifocal and disseminated
*Lesions similar to some infectious causes (such as [[Toxoplasma|''Toxoplasma gondii'']])

====Canine bilateral extraocular polymyositis====

*In Golden retrievers
*Very rare
*Clinical signs:
**Acute bilateral exophthalmos
*Involves only extraocular muscles except for retractor blbi
*Grossly:
**Swollen and pale extraocular muscles
*Histologically:
**Sterile myositis
**Multifocal necrosis of myofibres
**Lymphocytic, histiocytic and plasmacytic infiltrate with few [[Neutrophils - WikiBlood|neutrophils]]


====Bovine and ovine eosinophilic myositis====

*Unknown aetiology
*Major cell involved is eosinphil
*Usually noticed at slaughter - green muscle discoloration
*May be caused by degenteration of [[Sarcocystis|''Sarcocystis'' spp.]]
*Grossly:
**Green discolored areas, well demarcated
**Mostly in muscles of back and thighs
*Histologically:
**Massive eosinophil infiltration
**Muscle fibres may degenerate
**In old lesions - endimysial fibrosis, myofibre atrophy, some regeneration, lymphocytes, plasma cells, macrophages and few eosinophils
**Capsule may form