Joints Inflammatory - Pathology

Arthritis

Fibrinopurulent arthritis in cattle (Image sourced from Bristol Biomed Image Archive with permission)

Suppurative arthritis in cattle (Image sourced from Bristol Biomed Image Archive with permission)

• Inflammation of intra-articular structures
• In farm animals usually due to infection
• In small animals usually due to non-infectious causes

• Classification:
  • According to number of joints involved - polyarthritis
  • According to type of inflammatory exudate
    • Serous
      • Increased synovial fluid production
      • Resolves if uncomplicated
    • Fibrinous
      • Early stages:
        • Increased and more opaque synovial exudate
        • Enlarged hyperaemic villi
        • Small haemorrhages in synovial membrane
      • Later stages:
        • Less exudate
        • Thickend synovial connective tissue
        • Marked villi proliferation (branching in microscopic preparations)
        • Proliferated synovial tissue -> peripheral fibrous tissue attempting repair across defective surface = pannus
      • Mild cases resolve
      • More severe cases - residual inflammation remains
      • Most severe cases - organising fibrosis +/- ankylosis
    • Purulent
      • Usually from haemoatogenous spread e.g. neonatal navel ill
      • May extend from adjacent abscesses
      • More destructive
      • Erosion of articular surfaces to underlying bone
      • Forms abscesses
      • Possible fistulation to the skin

• Caused by:
  • Trauma
  • Infectious organisms (e.g. bacteria, viruses)
  • Foreign material (urate crystals = gout)
  • Immune-mediated disease

Infectious arthritis

• Bacterial arthritis
  • Most common in food animals, especially young
  • Portals of entry include:
    • Navel and GI tract -> bacteraemia
    • Haematogenously -> polyarthritis
    • Traumatic inoculation
    • Extension from bone or periarticular soft tissue

• Viral arthritis
  • Progressive inflammatory and degenerative joint disease
  • Synovitis with cartilage destruction
  • Chronic mononuclear inflammatory reactions

In Sheep

• Maedi visna virus
• Bacterial infections mostly affects lambs except for Mycoplasmal artheritis
• Erysipelothrix rhusiopathiae

• Corynebacterium pyogenes

• Streptococcus spp.

• Staphylococci

• Chlamydia sp.

In Pigs

• Erysipelothrix rhusiopathiae

• Corynebacterium pyogenes and Staphylococci

• Haemophilus suis and Haemophilus parasuis

• Mycoplasma hyosynoviae and M. hyorhinis

In Cattle

• Neonatal polyarthritis by:
  • Streptococcus spp.
    • Via umbilicus
    • Also involves eyes and meninges
  • Coliforms
    • Localises in joints and meninges in severe non-fatal neonatal colibacillosis
    • May remain as chronic arthritis in larger joints
• Infections at any age:
  • Corynebacterium pyogenes
    • Suppurative arthrtis
    • Often due to pebetrating wound into or close to joints
  • Mycoplasma spp.
    • May be respinsible for some chronic cases but difficult to prove as hard to isolate
    • Fibrinous polyarthritis
  • Chlamydia sp.
    • Severe disease in young calves
    • High mortality
    • Can be seen in smears of synovial fluid from swollen joints
    • Oedematous and hyperaemic surrounding tissue
    • Possibly due to intrauterine infection
  • Brucella abortus
    • Uncommonly localises in joints
    • Usually in carpal bursitis (hygroma) in cattle and bursitis in horses

In Horses

• Arthritis can occur following neonatal infections by:
  • Actinobacillus equuli
  • Streptococcus spp.
  • Coliforms
  • Salmonella

In Goats

• Caprine Arthrirtis Encephalitis Virus

In Dogs

• Staphylococci
  • May cause discospondylitis
  • Destructive inflammatory lesion
  • Bacterial localise in annulus fibrosis -> may spread to local bone

Non-infectious arthritis

• No causative agent has been found
• Seem to be immune-mediated diseases

Erosive

Rheumatoid arthritis

• Occurs in the dog, mainly smaller breeds
• Uncommon
• Progressive erosive polyarthritis
• Mostly involves elbows, stifles, carpal and tarsal joints
• Grossly:
  • Marked villus hypertrophy of synovial membrane
  • Cartilage erosion
  • Pannus and periarticular osteophyte formation
  • In severe cases ankylosis
• Histologically:
  • Hyperplasia of lining cells
  • Proliferative synovitis
  • Synovial membrane has fibrin deposits
  • Lymphoid and plasma cell infiltration
  • Surrounding haemorrhagic areas
  • Macrophages containing haemosiderin
  • Connective tissue may contain foci of necrosis
  • Areas of erosion of peripheral articular cartilage and underlying subchondral bone
• Pathogenesis:
  • May involve deposition of immune complexes within joints
  • Substances degrading cartilage are released by synovial cells and macrophages involved in pannus formation

Non-erosive

Systemic lupus erythematosus (SLE)

• Occurs in dogs
• Clinical signs:
  • Anaemia
  • Thrombocytopaenia
  • Polymyositis
  • Glomerulonephritis

In chronic diseases

• E.g. pyometra, otitis externa, endocarditis, enteritis
• Can lead to immune complex deposition in joints

Gout

• Occurs in humans, reptiles and birds (have no uricase enzyme)
• The urate triggers inflammation