What is synovitis?

What is Synovitis?

Synovitis is inflammation of the synovial membrane that lines joints, characterized by joint swelling associated with pain or stiffness. 1 This inflammation can affect any synovial-lined joint and is a key feature in various inflammatory arthritis conditions.

Clinical Features of Synovitis

Synovitis presents with several characteristic findings:

• Joint swelling and tenderness to palpation
• Morning stiffness (particularly prominent in inflammatory conditions)
• Pain with joint movement
• Reduced range of motion in affected joints
• Warmth over the affected joint

Synovitis can occur in various locations:

• Joints (particularly metacarpophalangeal, proximal interphalangeal, and metatarsophalangeal joints)
• Tendon sheaths (tenosynovitis)
• Bursae (bursitis)

Diagnosis of Synovitis

Clinical Examination

Clinical examination is the primary method for detecting synovitis 1. Key findings include:

• Joint swelling not caused by trauma or bony enlargement
• Pain with joint movement
• Morning stiffness (especially lasting >30 minutes in inflammatory arthritis)
• Positive "squeeze test" for hand and foot joint involvement

Advanced Imaging

In cases where clinical examination is inconclusive:

• Ultrasound: Superior to clinical examination for detecting synovitis 1

  • Can visualize synovial thickening and effusion
  • Power Doppler can assess vascularity/inflammation activity
  • Detection rate approximately 2.18-fold higher than clinical examination 1

• MRI: Also superior to clinical examination 1

  • Can detect synovial inflammation, bone marrow edema, and early erosions
  • Particularly useful for deep joints difficult to assess clinically
  • Detection rate approximately 2.20-fold higher than clinical examination 1

Types and Causes of Synovitis

Synovitis can be classified as:

1. Transient synovitis (lasting <3 months) 2

   • May resolve with appropriate treatment
   • Often associated with viral infections or trauma

2. Persistent synovitis (lasting >3 months) 2

   • Can lead to joint damage and disability if untreated
   • Often associated with chronic inflammatory conditions

Common causes include:

• Inflammatory arthritis:

  • Rheumatoid arthritis - characterized by symmetric polyarticular synovitis 3
  • Psoriatic arthritis - may present with dactylitis ("sausage digits") 1
  • Juvenile idiopathic arthritis

• Crystal-induced arthritis:

  • Gout - monosodium urate crystal deposition 1
  • Pseudogout - calcium pyrophosphate deposition

• Osteoarthritis - synovitis is increasingly recognized as an important component 4, 5

• Infectious causes:

  • Septic arthritis (rheumatological emergency requiring immediate treatment) 2
  • Lyme disease
  • Viral arthritis

Pathophysiology

Synovitis involves:

• Infiltration of inflammatory cells into the synovial membrane
• Increased vascularity of the synovial tissue
• Production of pro-inflammatory cytokines and proteolytic enzymes
• In chronic cases, synovial hyperplasia and pannus formation

In conditions like rheumatoid arthritis, this inflammatory process can lead to cartilage degradation and bone erosion if not adequately treated 5.

Treatment Approaches

Treatment depends on the underlying cause and severity:

1. For transient synovitis:

   • NSAIDs for pain and inflammation 6, 2
   • Rest and activity modification
   • Corticosteroids (oral or intra-articular) for more severe cases 6, 2

2. For persistent synovitis:

   • Disease-modifying antirheumatic drugs (DMARDs) for inflammatory arthritis 1
   • Methotrexate is considered the anchor drug for persistent inflammatory arthritis 1
   • Biological agents for refractory cases
   • Treatment should begin early to prevent joint damage 1

Clinical Importance

Early detection and treatment of synovitis is crucial because:

• Persistent synovitis can lead to irreversible joint damage
• Early intervention may prevent progression from transient to persistent synovitis 2
• Synovitis is associated with pain and functional limitation
• The presence of synovitis on imaging can predict future joint damage 1

Common Pitfalls

• Failing to distinguish between transient and persistent synovitis
• Missing septic arthritis, which requires urgent treatment
• Overlooking synovitis in osteoarthritis, where it contributes significantly to symptoms 4, 5
• Relying solely on clinical examination, which may miss synovitis detectable by imaging 1