Myositis
Viral Myositis
Parasitic Myositis
Immune-Mediated Myositis
Idiopathic myositis
Canine polymyositis
- DOES NOT include Masticatory Muscle Myositis
- 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 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
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 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