Joints Inflammatory - Pathology

()Map MUSCULOSKELETAL SYSTEM (Map) JOINTS

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
  • Clinical sighns:
    • Cutaneous erysipelas
    • Polyarthritis in lambs
    • Rarely fatal septicaemia
  • Enters via:
    • Cuts, abrasions
    • Castration or docking wounds
    • Haematogenous spread -> subacute or chronic fibrinopurulent polyarthritis
  • Morbidity up tp 50%
  • Affects mostly unthrifty lmbs
  • Fibrosis and osteophyte formation in later stages -> persistent lameness
• Corynebacterium pyogenes
  • May cause post-dipping joint infections
• Streptococcus spp.
  • Commonly cause suppurative polyarthritis in lambs
  • Naval infection -> bacteriamia -> polyarthritis
    • May also cause blindness and nervous signs if uvea or meninges are affected
  • Larger joints are more afected
    • May spread to other organs
• Staphylococci
  • Sporadically infect joints
  • May complicate 'tick-borne fever'
• Chlamydia sp.
  • Sporadic or outbreaks of lamb polyarthritis
  • High morbidity, low mortality
  • Commonly together with conjunctivitis
  • Most recover but may remain lame

In Pigs

• Erysipelothrix rhusiopathiae
  • Most important and most common cause of arthritis
  • Causes chronic serofibrinous polyarthritis
  • Also causes discospondylitis
    • Similar to discospondylitis in dogs
  • Thickening of synovial membrane lining + plus hyperaemia and villus formation + lymphocyte and plasma cell infiltration
  • Acute stage
    • Increased joint fluid + hot swollen joints
    • Also expresses as septicaemic and urticarial lesion on the back (diamond shaped)
    • May involve endocarditis as a sequel
  • Chronic stage
    • More commonly encountered
    • Erosion of articular surface of joints with formation of pannus +/- joint ankylosis
    • Vaccination prevents septicaemic and urticarial forms but has no effect on joints
      • Probably due to dead bacteria still stimulating host immune system
  • Septicaemia lo9calises in meninges and joints
  • Well known in piglets in their first two months of life
  • Expresses as acute fibrinopurulent arthritis
• Corynebacterium pyogenes and Staphylococci
  • Cause purulent arthritis
  • In one or more joints
  • Commonly contaminate wounds
• Haemophilus suis and H. parasuis
  • Cause Glasser's disease
  • Fibrinous polyserositis, polyarhritis, meningitis
• Mycoplasma hyosynovia and M. hyorhinis
  • Produce syndrome similar to Glasser's disease with milder expression
  • Menigitis is rare
  • Arthritis most consistent

In Cattle

• Neonatal polyarthritis by:
  • Streptococcus spp.
    • Via umbilicus
    • Also involves eyes and meninges
  • Coliforms
    • Localises in joints and meninges in sevee 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
  • Arthritis is commonly the main expression
  • Large limb joints are thickened
  • Carpal hygroma is often present
    • Subcutaneous cystic swelling on cranial surface of the knee, contains serous fluid
  • In advanced cases
    • Synovial villus hypertrophy
    • Necrosis
    • Mineralisation
    • Mononuclear cell infiltration
    • Pannus formation
    • Articular cartilage destruction

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