IgG4-Related Disease: Imitating A Great Imitator.

Immunoglobulin G4-related disease (IgG4-RD) is a rare, but increasingly recognized, multi-organ fibro-inflammatory condition characterized by distinct pathologic and histologic features. The clinical variability and relative novelty of IgG4-RD make accurate diagnosis of the condition quite challenging. We report a case of a 71-year-old man presenting with hypertrophy of the facial glands and generalized lymphadenopathy who was previously diagnosed with sarcoidosis. We recognized that he had atypical epidemiologic characteristic for sarcoidosis and his prior work-up documented elevated serum IgG4 to > 300 mg/dL. Immunostaining of an axillary lymph node biopsy showed an IgG4+/IgG+ plasma cell ratio of > 40% and a plasma cell concentration of > 100 IgG4+ plasma cells per high powered field, findings consistent with the diagnosis of IgG4-RD. This case report is an example of how analysis of collective clinicopathologic data led to a diagnosis of IgG4-RD. The pathologic complexities which contribute to the elusive nature of IgG4-RD are also illustrated.