View source for Muscles Inflammatory - Pathology

{{review}}

{{toplink
|backcolour =CDE472
|linkpage =Musculoskeletal System - Pathology
|linktext =Musculoskeletal System
|maplink = Musculoskeletal System (Content Map) - Pathology
|pagetype =Pathology
|sublink1=Muscles - Pathology
|subtext1=MUSCLES
}}
<br>
==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 pseudotuberculosis]]'' in sheep and goats
**[[Pasteurella multocida|''Pasteurella multocida'']] causes cellulitis in cats
*Usually localised suppuration and necrosis of myofibres
*Occasionally my spread via the fascia


====[[Black Leg]]====

====[[Gas Gangrene|Gas gangrene]]====

====[[Actinobacillosis|Wooden tongue]]====

====[[Tuberculosis]]====

====''[[Actinomyces bovis]]''====
*"[[Lumpy jaw]]"

====[[Botryomycosis]]====




===Viral myositis===

*Rare in the UK

====[[Porcine encephalomyelitis]]====

====[[Foot and Mouth Disease]]====


====[[Bluetongue Virus|Bluetongue]]====

===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====

*[[Trichinella|'''''Trichinella''''']] larvae


*[[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|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|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|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