What is synovitis?

Synovitis: Definition, Diagnosis, and Management

Synovitis is inflammation of the synovial membrane that lines joints, characterized by pain, swelling, and tenderness, which can lead to joint damage and disability if left untreated. 1

What is Synovitis?

Synovitis refers to inflammation of the synovial membrane, which is the soft tissue lining the spaces between joints, bursae, and tendon sheaths. The synovial membrane normally produces synovial fluid that lubricates and nourishes the joint. When inflamed, the synovium becomes thickened and produces excess fluid, leading to joint swelling and pain.

Classification of Synovitis:

• Transient synovitis: Lasts less than 3 months 2
• Persistent synovitis: Lasts more than 3 months, associated with higher risk of joint damage 2

Clinical Presentation

Synovitis typically presents with:

• Joint swelling
• Pain and tenderness
• Warmth over the affected joint
• Limited range of motion
• Morning stiffness (particularly in inflammatory arthritis)

The European League Against Rheumatism (EULAR) defines arthritis (with synovitis) as "joint swelling, associated with pain or stiffness" 3. Involvement of hand and foot joints is often suggested by a positive "squeeze test" 3.

Causes of Synovitis

Synovitis can occur in various conditions:

1. Inflammatory arthritides:

   • Rheumatoid arthritis
   • Psoriatic arthritis
   • Juvenile idiopathic arthritis

2. Crystal arthropathies:

   • Gout
   • Pseudogout

3. Other causes:

   • Osteoarthritis (increasingly recognized) 4
   • Trauma
   • Infection (septic arthritis)
   • Foreign body reaction (e.g., plant thorn synovitis) 5

Diagnosis

Clinical Examination

Clinical examination remains the cornerstone for detecting synovitis 3. Key findings include:

• Joint swelling
• Tenderness on palpation
• Warmth
• Limited range of motion

Imaging

While clinical examination is the method of choice, imaging can confirm synovitis when clinical findings are uncertain:

1. Ultrasonography (US):

   • Shows thickening of the synovial membrane with enhanced vascularity
   • Power Doppler techniques can detect increased blood flow in inflamed synovium
   • Sensitivity ranges from 37% to 100% and specificity from 68% to 97% 3
   • The double contour sign has a pooled sensitivity of 74% and specificity of 88% 3

2. Magnetic Resonance Imaging (MRI):

   • Highly sensitive for detecting synovitis
   • Can identify bone marrow edema, which is a strong predictor of disease progression 3
   • Useful for monitoring disease activity and treatment response

3. Conventional Radiography:

   • Less sensitive for early synovitis
   • Useful for detecting erosions and joint space narrowing in advanced disease

Laboratory Tests

• Complete blood count
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)
• Rheumatoid factor (RF) and anti-citrullinated peptide antibodies (ACPA)
• Synovial fluid analysis (gold standard for crystal arthropathies) 3

Management

Management depends on the underlying cause and severity of synovitis:

Transient Synovitis

• NSAIDs: First-line treatment for pain and inflammation
• Rest and activity modification
• Corticosteroids: For more severe cases, can be administered intra-articularly 2

Persistent Synovitis

Early treatment is crucial as EULAR guidelines state that "patients at risk of developing persistent or erosive arthritis should be started with DMARDs as early as possible" 3.

1. Disease-Modifying Antirheumatic Drugs (DMARDs):

   • Methotrexate is considered the anchor drug for persistent synovitis 3
   • Should be started ideally within six weeks of symptom onset 3

2. Biological agents: For cases unresponsive to conventional DMARDs

3. Intra-articular corticosteroid injections:

   • Provide rapid relief of local inflammation
   • Ultrasound can be used for accurate placement 3

4. Synovectomy:

   • Surgical option for refractory cases
   • Essential in cases of foreign body synovitis 5

Prognosis and Complications

If left untreated, persistent synovitis can lead to:

• Progressive joint damage
• Disability
• Reduced quality of life

Early diagnosis and treatment significantly improve outcomes, particularly in inflammatory arthritides like rheumatoid arthritis 1. Bone marrow edema on MRI is a strong independent predictor of radiographic progression in early rheumatoid arthritis 3.

Key Points for Clinical Practice

• Synovitis should be suspected in patients with joint pain, swelling, and stiffness
• Clinical examination is the primary method for detecting synovitis
• Ultrasound and MRI can confirm diagnosis in uncertain cases
• Early treatment is crucial to prevent joint damage and disability
• The treatment approach should target the underlying cause of synovitis
• Regular monitoring of disease activity should guide treatment decisions