Differential Diagnosis for Elevated Serum IgG4

Elevated serum IgG4 levels can be associated with various conditions. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • IgG4-Related Disease (IgG4-RD): This is a fibroinflammatory condition characterized by tumor-like swelling of affected organs, infiltration of IgG4-positive plasma cells, and variable degrees of fibrosis. The serum IgG4 concentration is often, but not always, elevated.

• Other Likely Diagnoses

  • Chronic Inflammatory Conditions: Certain chronic inflammatory diseases, such as rheumatoid arthritis, can sometimes show elevated IgG4 levels, although this is not a specific marker for these conditions.
  • Infections: Some infections, particularly parasitic infections, can lead to an increase in IgG4 levels as part of the immune response.
  • Allergic Diseases: Allergic conditions, including atopic dermatitis and asthma, may also exhibit elevated IgG4 levels, reflecting an allergic or immune response.

• Do Not Miss Diagnoses

  • Lymphoma: Although less common, certain types of lymphoma can present with elevated IgG4 levels. Missing this diagnosis could have significant implications for treatment and prognosis.
  • Sjögren's Syndrome: This autoimmune disorder can sometimes present with elevated IgG4 levels, and it's crucial to differentiate it from IgG4-RD due to differences in treatment approaches.

• Rare Diagnoses

  • Multicentric Castleman Disease: A rare disorder that can involve an increase in IgG4 levels among other immunoglobulins.
  • Hyper-IgG4 Syndrome: A condition characterized by recurrent infections, elevated IgG4 levels, and eczema, which is distinct from IgG4-RD.
  • Good’s Syndrome: A rare immunodeficiency disorder that might show elevated IgG4 levels, characterized by thymoma and impaired humoral immunity.

Each of these conditions has different implications for patient management and treatment, emphasizing the importance of a thorough diagnostic workup when elevated IgG4 levels are identified.