Joints Inflammatory - Pathology
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Arthritis
- 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
- Early stages:
- 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
- Serous
- 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
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 Haemophilus parasuis
- Cause Glasser's disease
- Fibrinous polyserositis, polyarhritis, meningitis
- Mycoplasma hyosynoviae 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
- Streptococcus spp.
- 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
- Corynebacterium pyogenes
In Horses
- Arthritis can occur following neonatal infections by:
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