Polyarthropathies

Question 1

Differential for polyarthropathies

Answer 1

Non immune mediated
- Degenerative (joint disease / OA)
- Hemorrhage
- Trauma
- Neoplasia
- Crystals (gout - rare)
- Infection : Aerobic cocci or rods, rickettsia, spirochets, mycoplasma, Bartonella, fungal, protozoal (Leishmania), viral.

Immune mediated primary
— Non erosive
- Idiopathic (type 1)
- SLE
- Breed associated
- Poly arthritis/polymyositis
- SRMA
— Erosive
- Rhumatoid arthritis
- Breed associated with
- Idiopathic

Secondary
- Systemic infection (type II)
- GI disease (type III)
- Non-joint neoplasia (type IV)
- Systemic or non-joint inflammatory disease
- Vaccine induced.

Question 2

Clinical presentation for IMPA

Answer 2

• Reluctance to walk, altered gait or lameness, multiple swollen painful joint
• Walking of egg shells
• Lameness might be present in different limbs at different times.
• Possible spinal pain —> due to inflammation of the articular facets joints vs concurrent inflammation present.

Other signs possible : fever, lethargy, inappetence and vomiting.

Question 3

What is the underlying etiology of IMPA

Answer 3

Synovial accumulation of immune complexes - type III hypersensitivity.

Erosive form : include a T cell mediated response (type IV hypersensitivity) directed against the articular cartilage.

Question 4

Diagnosis

Answer 4

Sample at least 3 joints (tarsus and carpus are the most commonly affected)
Make slide at fluid collection
Submit at least 1 joint for culture (high rate of false negative with septic arthritis)

Question 5

Joint aspirate results based on the result

Answer 5

Septic inflammatory : WBC > 15000/uL ; Neutrophils > 10% and TP > 2.5
Likely IMPA : WBC > 3000 ; Neutrophils > 10% and TP > 2.5
Non inflammatory : WBC < 5000/uL ; Neutrophils < 10% ; TP < 2.5 g/dL

In normal joint fluid, synoviocyte and macrophages are present

Mononuclear cells predominates in degenerative arthropathy or joint instability.

Other diagnostics to consider based on results
— Hemorrhage : look for erythrophagocytosis to help differentiate from blood contamination
— Degenerative arthropathy : joint radiographs
— Inflammatory arthropathy : test for infectious agents, consider ANA