Inflammatory joint disease in cats

Question 1

Give some examples of non-inflammatory disorders affecting the joints

Answer 1

Non-inflammatory conditions are the most common and include:
- developmental
- degenerative
- neoplastic
- traumatic injury

Question 2

How inflammatory conditions of the joints are categorized

Answer 2

Inflammatory joint disorders can be infectious or immune-mediated, and may affect one joint or multiple joints (polyarthritis)
- in cats, unlike dogs, infectious causes of arthritis are much more common than primary immune-mediated disorders

Polyarthritis is further classified as being erosive or non-erosive based on physical examination and radiographic findings

Question 3

Give some examples of infectious causes of arthritis in cats

Answer 3

Infectious causes of arthritis include:
- bacteria
- bacterial L-forms
- Mycoplasma species
- calicivirus
- FIP
- cryptoccocosis and histoplasmosis
- some tick-borne rickettsiae

Question 4

What type of inflammatory joint disease is caused by the most common agents

Answer 4

Most of the infectious agents cause non-erosive arthritis, with the possible exception of Mycoplasma species

Question 5

What is the pathomechanism for infectious arthritis

Answer 5

Infectious disorders primarily cause arthritis by direct inoculation of the synovium, but occasionally systemic infections give rise to circulating immune complexes that are deposited in joints, resulting in a sterile synovitis known as reactive polyarthritis

Question 6

What is the difference in the clinical presentation between inflammatory joint disease and osteoarthritis

Answer 6

Clinical manifestations of inflammatory joint diseases are typically more acute and severe than those seen in cats with osteoarthritis

Question 7

What are the typical clinical signs of polyarthritis

Answer 7

Cats present with a shifting-leg lameness or are reluctant to move

When inflammation is severe, affected joints are swollen and painful

Erosive disorders may cause palpable joint instability or deformity

Systemic signs of inflammation, including lethargy, anorexia and fever, are common, although some cats with chronic low grade joint inflammation are normal with slowly progressive lameness and joint deformity

Question 8

Which clinical findings could help differentiate OA from inflammatory joint disorder

Answer 8

Many cats with OA have joints that are normal on palpation, whereas pain and swelling are present in most inflamed joints

Question 9

What are the main differentials for inflammatory joint disorders

Answer 9

Inflammatory arthritis is uncommon in cats

Most cats presenting with vague signs such as lethargy, inappetence and fever have a cat bite abscess, pancreatitis or a viral infection

Question 10

How can you confirm a diagnosis of inflammatory arthritis

Answer 10

Synovial fluid collection and analysis is required to confirm a diagnosis of inflammatory arthritis

Synovial fluid should be collected and evaluated from at least five joints, even in cats with apparent monoarticular inflammation, since one joint is often more obviously inflamed and painful than others in cats with polyarthritis
- fluid should always be collected from joints that are swollen and painful

Question 11

What is the general repartition of inflammaed joints according to the cause

Answer 11

Immunologically mediated disease tends to be most pronounced in the distal small joints, such as the hock and carpus

Bacterial infective arthritis is most likely to affect larger joints like the stifle and elbow in dogs
- that is not necessarily the case in cats, where infections often occur following cat bite inoculation of distal joints

Question 12

Describe the arthrocentesis procedure

Answer 12

General anesthesia is recommended

The site should be clipped, the skin surgically prepared, and sterile gloves, needles and syringes used
- a 22G 1 inch needle is used

The needle should be connected to a ml syringe and introduced into the joint
- once the tip of the needle is in the joint space, gentle negative pressure is applied to the syringe

Once fluid is obtained, negative pressure is released and the needle is withdrawn from the skin

The needle is disconnected from the syringe, air is drawn into the syringe, the needle is reattached, and the air is used to expel a drop of synovial fluid onto a microscope slide to assess viscosity, color and clarity

Then a smear is made for cytologic evaluation

Question 13

How is the normal synovial fluid

Answer 13

Normal joint fluid is:
- very viscous (due to high hyaluronic acid content)
- colorless
- clear

Question 14

How would you interpret synovial fluid anomalies

Answer 14

Diffuse hemorrhagic or yellow discoloration suggests prior intra-articular hemorrhage

Turbidity suggests an increase in red or white blood cell count

Reduced viscosity suggests inflammation

Absolute cell counts are rarely performed because sample are small
- cell numbers should be less than 3000 cells/µl
- most cells are mononuclear (>90%) and neutrophils represent less than 10%

Question 15

How would you interpret an increase in the number of neutrophils in the synovial fluid

Answer 15

An increase in the number of neutrophils, to greater than 10% of the TNCC, indicates that there is inflammation of the synovial lining
- the more inflamed the synovium, the greater the number of WBC and the greater the percentage of neutrophils

Neutrophils in synovial fluid from joints with immune-mediated disease will have a normal appearance, as will neutrophils from joints affected by rickettsial polyarthritis

In acute or severe septic arthritis, neutrophils may appear toxic, ruptured or degenerate and intracellular bacteria may be seen
- inflammatory joint fluid should always be cultured, because some organisms (e.g., mycoplasma) do not induce these cytologic abnormalities

Question 16

Direct bacterial culture of synovial fluid is positive in only about half all cases of spetic arthritis. How can you increase the sensitivity of culture

Answer 16

The use of broth-enrichment media (e.g., thioglycolate blood culture bottles) and incubation for 24 h prior to culture greatly increases the rate of positive culture (>85%)

Question 17

What would be your diagnostic plan (except for synovial fluid analysis) for a cat suffering inflammatory joint disease

Answer 17

All cats with inflammatory joint disease should be tested for FeLV and FIV since:
- immunosuppression may be an important predisposition for infectious arthritis
- FeLV has been implicated in the development of periosteal proliferative polyarthritis

Immunologic and serologic testing for Borrelia, rickettsiae may be warranted

When reactive polyarthritis is a possibility, a complete blood count, biochemical panel, urinalysis, thoracic and abdominal radiographs, abdominal US, culture of urine and blood, and lymph node aspirates should be recommended in order to identify underlying chronic infections or neoplasia

Question 18

Explain why radiographs are important in the investigation of a cat with inflammatory joint disorder

Answer 18

Radiographs are an important part of the initial evaluation of cats with mono- or polyarthritis in order to determine whether their disease is erosive or non-erosive

Incidental radiographic abnormalities due to OA are common in cats
- feline OA causes osteophytes and periarticular and meniscal mineralization, not the synovial effusion, destructive “punched out” subchondral and periarticular lesions, and joint subluxation associated with erosive disease

Question 19

What are the key features for bacterial arthritis

Answer 19

A cat bite wound penetrating the joint is the most common cause of feline septic arthritis
- Pasteurella species and coliforms are most often incriminated

Septic arthritis due to a cat fight usually involves only one joint, and the carpus, hock and interphalangeal joints are at highest risk

Bacterial infection of multiple joints is rare, but can be seen in neonatal kittens with omphalophlebitis

Cats with septic arthritis are often:
- systemically ill
- febrile
- depressed
- with painful affected joints and periarticular swelling

Amoxicillin-clavulanic acid is the first line therapy

Question 20

What are the key features of Mycoplasma arthritis

Answer 20

Mycoplasma are normal inhabitants of the conjunctival membranes, pharynx and upper respiratory and urogenital tracts

Mycoplasma polyarthritis occurs primarily in debilitated or immunosuppressed animals, but has also been described in apparently immunocompetent cats
- cats should be tested for FIV, FeLV, lymphoma and other immunosuppressive disorders

Mycoplasma polyarthritis typically results from hematogennous spread of the bacteria to the joints

Cytological analysis of synovial fluid shows the same anomalies as non-infectious immune-mediated arthritis
- inflammatory joint fluid from cats should always be specifically cultured for Mycoplasma and empirical treatment with oral doxycycline for 3 weeks is recommended before treating culture-negative polyarthritis with immunosuppressant drugs

Mycoplasma polyarthritis has been described as being primarily non-erosive but erosions can occur

Treatment is with doxycycline or fluoroquinolones for 6-8 weeks

Question 21

What are the key features of bacterial L-form associated arthritis

Answer 21

L-forms of bacteria are cell wall-deficient forms morphologically similar to Mycoplasma
- they have been isolated from cats with a syndrome of fever, cellulitis and polyarthritis

Cats are infected by direct inoculation and the infection spreads locally and hematogenously to cause cellulitis, draining tracts, polyarthritis and subcutaneous abscesses

The infection is resistant to many antibiotics except to tetracycline and fluoroquinolone

Question 22

How frequent are non-infectious inflammatory joint disorders in cats

Answer 22

They are rare

All cats with polyarthritis should be evaluated for an infectious cause and also for a systemic infectious or neoplastic reason for reactive polyarthritis

Question 23

Regarding the low frequence of non-infectious inflammatory joint disorders in cats, what would be prudent to do even when all tests are negative

Answer 23

Even when all tests are negative it is prudent to treat empircally for 14 days with doxycycline to gauge response before making a diagnosis of primary immune-mediated disease

Question 24

What is the pathomechanism for non-erosive immune-mediated polyarthritis

Answer 24

Non-erosive immune-mediated polyarthritis is caused by deposition of immune complexes in the synovial membrane and the ensuing inflammatory response

This can occur as:
- a primary or idiopathic disorder
- secondarily to antigenic stimulation (reactive polyarthritis)
- as a feature of systemic lupus erythematosus

Question 25

How are radiographic changes in non-erosive immune-mediated polyarthritis

Answer 25

Radiographic changes, even after many months of joint disease, are minimal to non-existent and are limited to soft tissue swelling

Question 26

How can you make a diagnosis of primary (idiopathic) immune-mediated polyarthritis

Answer 26

Primary or idiopathic immune-mediated polyarthritis can be diagnosed in a cat with non-erosive polyarthritis when: - infectious etiologies have been eliminated - there is no evidence to support systemic lupus erythematosus or reactive polyarthritis

Question 27

When you suspect primary immune-mediated polyarthritis in a cat, when can you start glucocorticoids

Answer 27

When thorough diagnostic evaluation suggests IMPA and a cat does not respond to empirical doxycycline, treatment with glucocorticoids is warranted

Question 28

What would be your treatment plan for cats with idiopathic immune-mediated polyarthritis

Answer 28

Prednisolone 2 mg/kg, PO, q12h for 3-4 days then Prednisolone 2 mg/kg, PO, q24h for 4 weeks then Assess clinical response and perform synovial fluid cytology - if clinical signs have resolved, gradually taper the prednisolone dose - if clinical signs are still present or joint inflammation is present, restart prednisolone 2 mg/kg, PO, q24h and add another immunosuppressive drug

Question 29

What immunosuppressive drugs can be used for idiopathic polyarthritis

Answer 29

Prednisolone 2 mg/kg, q12h then taper Ciclosporin 4 mg/kg, PO, q12h Leflunomide 10 mg/cat, PO, q24h Chlorambucil 2 mg/cat, PO, q48h Methotrexate 2.5 mg/m2, PO, q48h

Question 30

What are the key features for feline periosteal proliferative polyarthritis

Answer 30

Epidemiology: - most common in young adult males Clinical signs: - fever, lethargy - a stiff gait - joint pain and swelling (particularly of the carpus and hock) - sometimes edema of the skin and soft tissues overlying the joints - lymph node hyperplasia may cause severe regional lymphadenopathy Diagnostic tests: - synovial fluid analysis reveals a moderate-to-severe neutrophilic pleocytosis and culture is negative - radiographic changes may not be evident for the first 12 weeks of illness then early findings include: - periarticular soft tissue swelling - mild periosteal proliferation - over time, the periosteal proliferation worsens and extends beyond the confines of the joint, which may lead to ankylosis - Periarticular osteophytes, subchondral cyst-like lesions and periarticular erosions are evident - synovial biopsies initially reveal neutrophilic synovitis and tenosynovitis, but with chronicity, the proportion of lymphocytes and plasma cells increases Treatment: - glucocorticoids lessen the severity of signs and may slow progression of disease, but they are not curative

Question 31

What are the key features for feline rheumatoid-like arthritis

Answer 31

Epidemiology: - middle-aged and older cats most often affected - Siamese may be overrepresented Clinical signs: - it has an insidious onset, with lameness and joint deformity developing slowly over weeks to months - lameness is often noticed by the owner in only one limb but careful examination reveals swelling and pain affecting multiple distal joints - systemic illness and fever do not occur, so these cats are rarely evaluated before severe joint deformities are evident Diagnostic tests: - synovial fluid analysis reveals an increased TNCC with mixed inflammation (PNN are usually predominant) - synovial biopsy reveals chronic synovitis and villous hypertrophy of the synovial membrane, with dense lymphoid and plasma cell infiltrates destroying articular cartilage - radiographs show severe subchondral central and marginal erosions, and periarticular soft tissue swelling, periosteal new bone formation is minimal - a positive RF test is not essential or sufficient for diagnosis, but results have been positive in most reports in the literature of cats with rheumatoid-like arthritis Treatment: - rheumatoid-like arthritis is an aggressive, destructive, irreversible disease if early therapy is not administered - most cats have only a minimal response to NSAIDs or glucocorticoids - methotrexate in combination with leflunomide can result in marked clinical improvement - most cats also require analgesic medications (e.g., buprenorphine, gabapentin)

Question 32

What are the different subgroups of idiopathic immune-mediated polyarthritis

Answer 32

Type I IMPA - idiopathic IMPA - the most common non-erosive IMPA - not associated with an extra-articular disease Type II IMPA - idiopathic associated with infection remote from the joint (e.g., endocarditis, respiratory infection, urogenital infection) Type III IMPA - idiopathic associated with gastrointestinal disease (frequently diarrhea, occasional vomiting) Type IV IMPA - idiopathic associated with neoplasia (paraneoplastic arthritis) - in the cat this is most often myeloproliferative neoplasia, which may be FeLV or FIV related

Question 33

What are the criteria proposed for the diagnosis of periosteal proliferative polyarthritis

Answer 33

The criteria are: - erosive polyarthritis - periosteal nex bone formation in affected joints - negative rheumatoid factor blood test - enthesopathy (i.e., new bone formation at attachment points of ligaments, tendons or fascia) - primarily the hocks and carpi are involved The first three criteria must be met to make the diagnosis; the last two are variable