Differential Diagnosis for Bilateral MCP Synovitis

• Single most likely diagnosis
  • Rheumatoid Arthritis (RA): This is the most common cause of bilateral metacarpophalangeal (MCP) joint synovitis, characterized by symmetric joint involvement, morning stiffness, and systemic symptoms such as fatigue and fever. The presence of autoantibodies like rheumatoid factor (RF) and anti-citrullinated protein antibody (anti-CCP) supports this diagnosis.
• Other Likely diagnoses
  • Psoriatic Arthritis (PsA): This condition can cause asymmetric or symmetric joint involvement, including the MCP joints, and is often associated with psoriatic skin lesions, nail changes, and dactylitis.
  • Osteoarthritis (OA): Although OA more commonly affects the distal interphalangeal joints, it can also involve the MCP joints, especially in the context of erosive OA, which may present with inflammatory features.
  • Systemic Lupus Erythematosus (SLE): SLE can cause arthritis that resembles RA, with symmetric joint involvement, but it is also associated with a wide range of systemic symptoms and autoantibodies, including antinuclear antibodies (ANA).
• Do Not Miss diagnoses
  • Septic Arthritis: Although less common, septic arthritis is a medical emergency that requires prompt diagnosis and treatment to prevent joint destruction and systemic complications. It typically presents with acute onset of pain, swelling, and decreased range of motion in a single joint, but can be bilateral in the context of certain infections or in immunocompromised patients.
  • Crystal Arthropathies (Gout or Pseudogout): These conditions can cause acute or chronic synovitis and should be considered, especially if there are sudden onset, intense pain, and swelling, or if there is a history of similar episodes.
• Rare diagnoses
  • Sjögren's Syndrome: This autoimmune disorder can cause arthritis similar to RA, but it is primarily known for its exocrine gland involvement, leading to dry eyes and dry mouth.
  • Mixed Connective Tissue Disease (MCTD): MCTD has features that overlap with SLE, RA, and scleroderma, and can cause arthritis, including MCP joint synovitis.
  • Hemochromatosis: This genetic disorder leads to iron overload and can cause arthritis, typically affecting the second and third MCP joints, among other joints.
  • Whipple's Disease: A rare, systemic bacterial infection that can cause arthritis, among other symptoms, and requires specific antibiotic treatment.