IgG4-related disease

This code identifies a chronic, immune-mediated fibroinflammatory condition characterized by tissue infiltration of IgG4-positive plasma cells, storiform fibrosis, and often elevated serum IgG4 levels. It can affect nearly any organ system, leading to mass lesions, organ enlargement, or dysfunction.

Assign this code when documentation confirms a diagnosis of IgG4-related disease, such as autoimmune pancreatitis, IgG4-related cholangitis, or orbital pseudotumor, where the underlying etiology is identified as IgG4-related. Supporting documentation includes biopsy results showing characteristic histopathology, elevated serum IgG4, and clinical presentation consistent with the disease.

• Do not use this code for isolated elevated serum IgG4 without a confirmed diagnosis of IgG4-related disease.
• Code any specific organ manifestations (e.g., K86.1 for other chronic pancreatitis) in addition to this code, if applicable.
• Ensure the provider's documentation clearly states "IgG4-related disease" or a specific IgG4-related condition.