What is synovitis?

Synovitis: Inflammation of the Synovial Membrane

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, 2

Definition and Pathophysiology

Synovitis refers to inflammation of the synovial membrane (synovium), which is a specialized tissue that:

• Lines the inner surface of joint capsules
• Produces synovial fluid that lubricates joints
• Provides nutrients to articular surfaces 3

When inflamed, the synovium undergoes several changes:

• Hyperplasia of the lining layer
• Increased vascularity (neo-angiogenesis)
• Infiltration of immune cells
• Production of inflammatory mediators 4

Clinical Presentation

Synovitis typically manifests as:

• Joint pain and tenderness
• Swelling due to increased synovial fluid
• Stiffness, particularly morning stiffness
• Reduced range of motion
• Warmth over the affected joint 1, 2

Classification

Synovitis can be classified based on duration:

1. Transient synovitis (< 3 months)

   • Often self-limiting
   • May respond to conservative treatment 2

2. Persistent synovitis (> 3 months)

   • Associated with higher risk of joint damage
   • May indicate underlying chronic inflammatory disease
   • Requires more aggressive treatment 2

Causes and Associations

Synovitis is commonly associated with:

1. Inflammatory arthritides

   • Rheumatoid arthritis (RA) - most common cause of persistent synovitis 1
   • Psoriatic arthritis (PsA) 1
   • Other spondyloarthropathies

2. Osteoarthritis (OA)

   • Synovitis plays a key role in OA pathophysiology
   • Associated with clinical symptoms and disease progression 5

3. Crystal arthropathies

   • Gout
   • Calcium pyrophosphate deposition disease (pseudogout) 1

4. Infectious causes

   • Septic arthritis (rheumatological emergency) 2

5. Other conditions

   • SAPHO syndrome (Synovitis, Acne, Pustulosis, Hyperostosis, Osteitis) 6
   • Trauma-related synovitis

Diagnostic Approach

Clinical Assessment

• Joint examination for swelling, tenderness, and range of motion
• Assessment of pattern (oligoarticular vs. polyarticular, symmetric vs. asymmetric)
• Evaluation of morning stiffness duration

Laboratory Testing

• Rheumatoid factor (RF) testing in suspected RA 1, 7
• Anti-cyclic citrullinated peptide (anti-CCP) antibodies if RF negative 1, 7
• Inflammatory markers (ESR, CRP) - may be normal in up to 40% of cases 7
• Joint fluid analysis when infection is suspected 2

Imaging

1. Radiography

   • First-line imaging
   • May show periarticular osteopenia, joint space narrowing, erosions in established disease 1

2. Ultrasound (US)

   • Highly sensitive for detecting synovitis
   • Can show inflammation as active synovitis
   • Power Doppler assessment useful for identifying active inflammation 1

3. Magnetic Resonance Imaging (MRI)

   • Gold standard for non-invasive detection of synovitis
   • Can detect subclinical inflammation
   • Particularly useful with IV contrast to quantify active synovitis 1
   • Can identify bone marrow edema (osteitis), a strong predictor of disease progression in RA 1

Management

Treatment approach depends on the underlying cause and duration:

Transient Synovitis

• Analgesics for pain relief
• NSAIDs to reduce inflammation
• Rest and activity modification
• Corticosteroid injections for severe cases 2

Persistent Synovitis

• Disease-modifying antirheumatic drugs (DMARDs) for underlying inflammatory conditions
• Early treatment is crucial to prevent joint damage
• Urgent referral to rheumatology for suspected persistent synovitis 1, 2

Specific Recommendations

• Refer urgently for specialist opinion anyone with suspected persistent synovitis, especially if:
  • Small joints of hands/feet are affected
  • Multiple joints are involved
  • Symptoms have persisted for ≥3 months 1

Prognosis

The prognosis of synovitis varies based on:

• Underlying cause
• Duration before treatment initiation
• Response to therapy

Untreated persistent synovitis can lead to:

• Progressive joint damage
• Disability
• Reduced quality of life 2, 4

Early diagnosis and treatment significantly improve outcomes, particularly in inflammatory arthritides like RA 1, 2.