Muscles Inflammatory - Pathology

Myositis

Bacterial 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